Second immunoglobulin (Ig)-like domain of nectin-like molecule-3 (Necl-3); member of the I-set of Ig superfamily domains; The members here are composed of the second immunoglobulin (Ig)-like domain of nectin-like molecule-3 (Necl-3; also known as cell adhesion molecule 2 (CADM2)). Nectin-like molecules have similar domain structures to those of nectins. At least five nectin-like molecules have been identified (Necl-1 through Necl-5). These have an extracellular region containing three Ig-like domains, one transmembrane region, and one cytoplasmic region. Necl-3 has been shown to accumulate in tissues of the central and peripheral nervous system where it is expressed in ependymal cells and myelinated axons. It is observed at the interface between the axon shaft and the myelin sheath. Ig domains are likely to participate in ligand binding and recognition.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145  79 VLGVPEKPQISGFSSPVMEGDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGV 158
Cdd:cd05884     1 VLGVPEKPQISGFTSPVMEGDHIQLTCKTSGSKPAADIRWFKNDKEVKDVKYLKAEDANRKTFTVSSSLDFHVDRDDDGV 80

                          90       100
                  ....*....|....*....|....
gi 1773401145 159 AVICRVDHESLNATPQVAMQVLEI 182
Cdd:cd05884    81 AITCRVDHESLTATPQIAMQVLEI 104

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 1773401145 186 PSVKIIPSTPFPQEGQPLILTCESKGKPLPEpVLWTKDGGELPD----PDRMVVSGRELNILFLNKTDNGTYRCEATN 259
Cdd:pfam13927   2 PVITVSPSSVTVREGETVTLTCEATGSPPPT-ITWYKNGEPISSgstrSRSLSGSNSTLTISNVTRSDAGTYTCVASN 78

Second immunoglobulin (Ig)-like domain of nectin-like molecule-3 (Necl-3); member of the I-set of Ig superfamily domains; The members here are composed of the second immunoglobulin (Ig)-like domain of nectin-like molecule-3 (Necl-3; also known as cell adhesion molecule 2 (CADM2)). Nectin-like molecules have similar domain structures to those of nectins. At least five nectin-like molecules have been identified (Necl-1 through Necl-5). These have an extracellular region containing three Ig-like domains, one transmembrane region, and one cytoplasmic region. Necl-3 has been shown to accumulate in tissues of the central and peripheral nervous system where it is expressed in ependymal cells and myelinated axons. It is observed at the interface between the axon shaft and the myelin sheath. Ig domains are likely to participate in ligand binding and recognition.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145  79 VLGVPEKPQISGFSSPVMEGDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGV 158
Cdd:cd05884     1 VLGVPEKPQISGFTSPVMEGDHIQLTCKTSGSKPAADIRWFKNDKEVKDVKYLKAEDANRKTFTVSSSLDFHVDRDDDGV 80

                          90       100
                  ....*....|....*....|....
gi 1773401145 159 AVICRVDHESLNATPQVAMQVLEI 182
Cdd:cd05884    81 AITCRVDHESLTATPQIAMQVLEI 104

CD80-like C2-set immunoglobulin domain; These domains belong to the immunoglobulin superfamily.

                          10        20        30        40        50        60
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 1773401145 103 LTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGVAVICRVDHESL 169
Cdd:pfam08205  19 ATCSSAGGKPAPRITWYLDGKPLEAAETSSEQDPESGLVTVTSELKLVPSRSDHGQSLTCQVSYGAL 85

Third immunoglobulin (Ig)-like domain in Robo (roundabout) receptors; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the third immunoglobulin (Ig)-like domain in Robo (roundabout) receptors. Robo receptors play a role in the development of the central nervous system (CNS), and are receptors of Slit protein. Slit is a repellant secreted by the neural cells in the midline. Slit acts through Robo to prevent most neurons from crossing the midline from either side. Three mammalian Robo homologs (Robo1, Robo2, Robo3), and three mammalian Slit homologs (Slit-1,Slit-2, Slit-3), have been identified. Commissural axons, which cross the midline, express low levels of Robo; longitudinal axons, which avoid the midline, express high levels of Robo. Robo1, Robo2, and Robo3 are expressed by commissural neurons in the vertebrate spinal cord and Slit-1, Slit-2, and Slit-3 are expressed at the ventral midline. Robo-3 is a divergent member of the Robo family which instead of being a positive regulator of Slit responsiveness, antagonizes Slit responsiveness in precrossing axons. The Slit-Robo interaction is mediated by the second leucine-rich repeat (LRR) domain of Slit and the two N-terminal Ig domains of Robo, Ig1 and Ig2. The primary Robo binding site for Slit2 has been shown by surface plasmon resonance experiments and mutational analysis to be the Ig1 domain, while the Ig2 domain has been proposed to harbor a weak secondary binding site. This group belongs to the I-set of IgSF domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. Like the V-set Ig domains, members of the I-set have a discontinuous A strand, but lack a C" strand.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|...
gi 1773401145 200 GQPLILTCESKGKPLPEpVLWTKDGGELPDPDRMVVSGRELNILFLNKTDNGTYRCEATNTIGQSSAEYVLIV 272
Cdd:cd05725    12 DDSAEFQCEVGGDPVPT-VRWRKEDGELPKGRYEILDDHSLKIRKVTAGDMGSYTCVAENMVGKIEASATLTV 83

putative band 4.1 homologues' binding motif;

                           10
                   ....*....|....*....
gi 1773401145  307 LGRYLARHKGTYLTNEAKG 325
Cdd:smart00294   1 MYRYKHRDEGSYHTHEPKG 19

Second immunoglobulin (Ig)-like domain of nectin-like molecule-3 (Necl-3); member of the I-set of Ig superfamily domains; The members here are composed of the second immunoglobulin (Ig)-like domain of nectin-like molecule-3 (Necl-3; also known as cell adhesion molecule 2 (CADM2)). Nectin-like molecules have similar domain structures to those of nectins. At least five nectin-like molecules have been identified (Necl-1 through Necl-5). These have an extracellular region containing three Ig-like domains, one transmembrane region, and one cytoplasmic region. Necl-3 has been shown to accumulate in tissues of the central and peripheral nervous system where it is expressed in ependymal cells and myelinated axons. It is observed at the interface between the axon shaft and the myelin sheath. Ig domains are likely to participate in ligand binding and recognition.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145  79 VLGVPEKPQISGFSSPVMEGDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGV 158
Cdd:cd05884     1 VLGVPEKPQISGFTSPVMEGDHIQLTCKTSGSKPAADIRWFKNDKEVKDVKYLKAEDANRKTFTVSSSLDFHVDRDDDGV 80

                          90       100
                  ....*....|....*....|....
gi 1773401145 159 AVICRVDHESLNATPQVAMQVLEI 182
Cdd:cd05884    81 AITCRVDHESLTATPQIAMQVLEI 104

Second immunoglobulin (Ig)-like domain of nectin-like molcule-1 (Necl-1); member of the I-set of Ig superfamily domains; The members here are composed of the second immunoglobulin (Ig)-like domain of nectin-like molcule-1 (Necl-1; also known as cell adhesion molecule3 (CADM3)). These nectin-like molecules have similar domain structures to those of nectins. At least five nectin-like molecules have been identified (Necl-1 through Necl-5). These have an extracellular region containing three Ig-like domains, one transmembrane region, and one cytoplasmic region. The N-terminal Ig-like domain of the extracellular region belongs to the V-type subfamily of Ig domains is essential to cell-cell adhesion and plays a part in the interaction with the envelope glycoprotein D of various viruses. Necl-1 and Necl-2 have Ca(2+)-independent homophilic and heterophilic cell-cell adhesion activity. Necl-1 is specifically expressed in neural tissue and is important to the formation of synapses, axon bundles, and myelinated axons. Necl-2 is expressed in a wide variety of tissues and is a putative tumour suppressor gene which is downregulated in aggressive neuroblastoma. Ig domains are likely to participate in ligand binding and recognition.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145  80 LGVPEKPQISGFSSPVMEGDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGVA 159
Cdd:cd07705     1 LGIPQKPQITGYESAFKEKDKAKLRCTSSGSKPAANIKWRKGDQELEGAPTSVQEDGNGKTFTVSSSVEFQVTREDDGAE 80

                          90       100
                  ....*....|....*....|...
gi 1773401145 160 VICRVDHESLNATPQVAMQVLEI 182
Cdd:cd07705    81 ITCSVGHESLHDSDRSTSQRIEV 103

First (N-terminal) immunoglobulin (Ig)-like domain of the nectin-like molecules; member of the V-set of Ig superfamily (IgSF) domains; The members here are composed of the N-terminal immunoglobulin (Ig)-like domain of the nectin-like molecules Necl-1 (also known as cell adhesion molecule 3 (CADM3)), Necl-2 (CADM1), Necl-3 (CADM2), and similar proteins. At least five nectin-like molecules have been identified (Necl-1 to Necl-5). They all have an extracellular region containing three Ig-like domains, a transmembrane region, and a cytoplasmic region. The N-terminal Ig-like domain of the extracellular region belongs to the V-type subfamily of Ig domains, is essential to cell-cell adhesion, and plays a part in the interaction with the envelope glycoprotein D of various viruses. Necl-1, Necl-2, and Necl-3 have Ca(2+)-independent homophilic and heterophilic cell-cell adhesion activity. Necl-1 is specifically expressed in neural tissue, and is important to the formation of synapses, axon bundles, and myelinated axons. Necl-2 is expressed in a wide variety of tissues and is a putative tumour suppressor gene which is downregulated in aggressive neuroblastoma. Necl-3 accumulates in central and peripheral nervous system tissue and has been shown to selectively interact with oligodendrocytes. This group also contains Class-I MHC-restricted T-cell-associated molecule (CRTAM), whose expression pattern is consistent with its expression in Class-I MHC-restricted T-cells.

                          10        20        30        40        50
                  ....*....|....*....|....*....|....*....|....*....|....
gi 1773401145  26 NKVKALRDNRIELVRASWHELSISVSDVSLSDEGQYTCSLFTMPVKTSKAYLTV 79
Cdd:cd05717    41 NDKRALRDSRYQLLNHSASELSISVSNVTLSDEGVYTCLHYTDPVSTKKVTVTV 94

Second immunoglobulin (Ig)-like domain of nectin-like molecule-4 (Necl-4); member of the I-set of Ig superfamily domains; The members here are composed of the second immunoglobulin (Ig)-like domain of nectin-like molecule-4 (Necl-4; also known as cell adhesion molecule 4 (CADM4)). Nectin-like molecules have similar domain structures to those of nectins. At least five nectin-like molecules have been identified (Necl-1-Necl-5). These have an extracellular region containing three Ig-like domains, one transmembrane region, and one cytoplasmic region. Ig domains are likely to participate in ligand binding and recognition. Necl-4 is expressed on Schwann cells, and plays a key part in initiating peripheral nervous system (PNS) myelination. In injured peripheral nerve cells, the mRNA signal for both Necl-4 and Necl-5 was observed to be elevated. Necl-4 participates in cell-cell adhesion and is proposed to play a role in tumor suppression.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145  83 PEKPQISgFSSPVMEGDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEedaNRKTFTVSSTLDFRVDRSDDGVAVIC 162
Cdd:cd05885     4 PENPVVE-VREQAVEGGEVELSCLVPRSRPAATLRWYRDRKELKGVSSGQE---NGKVWSVASTVRFRVDRKDDGGIVIC 79

                  ....*..
gi 1773401145 163 RVDHESL 169
Cdd:cd05885    80 EAQNQAL 86

CD80-like C2-set immunoglobulin domain; These domains belong to the immunoglobulin superfamily.

                          10        20        30        40        50        60
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 1773401145 103 LTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGVAVICRVDHESL 169
Cdd:pfam08205  19 ATCSSAGGKPAPRITWYLDGKPLEAAETSSEQDPESGLVTVTSELKLVPSRSDHGQSLTCQVSYGAL 85

Third immunoglobulin (Ig)-like domain in Robo (roundabout) receptors; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the third immunoglobulin (Ig)-like domain in Robo (roundabout) receptors. Robo receptors play a role in the development of the central nervous system (CNS), and are receptors of Slit protein. Slit is a repellant secreted by the neural cells in the midline. Slit acts through Robo to prevent most neurons from crossing the midline from either side. Three mammalian Robo homologs (Robo1, Robo2, Robo3), and three mammalian Slit homologs (Slit-1,Slit-2, Slit-3), have been identified. Commissural axons, which cross the midline, express low levels of Robo; longitudinal axons, which avoid the midline, express high levels of Robo. Robo1, Robo2, and Robo3 are expressed by commissural neurons in the vertebrate spinal cord and Slit-1, Slit-2, and Slit-3 are expressed at the ventral midline. Robo-3 is a divergent member of the Robo family which instead of being a positive regulator of Slit responsiveness, antagonizes Slit responsiveness in precrossing axons. The Slit-Robo interaction is mediated by the second leucine-rich repeat (LRR) domain of Slit and the two N-terminal Ig domains of Robo, Ig1 and Ig2. The primary Robo binding site for Slit2 has been shown by surface plasmon resonance experiments and mutational analysis to be the Ig1 domain, while the Ig2 domain has been proposed to harbor a weak secondary binding site. This group belongs to the I-set of IgSF domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. Like the V-set Ig domains, members of the I-set have a discontinuous A strand, but lack a C" strand.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|...
gi 1773401145 200 GQPLILTCESKGKPLPEpVLWTKDGGELPDPDRMVVSGRELNILFLNKTDNGTYRCEATNTIGQSSAEYVLIV 272
Cdd:cd05725    12 DDSAEFQCEVGGDPVPT-VRWRKEDGELPKGRYEILDDHSLKIRKVTAGDMGSYTCVAENMVGKIEASATLTV 83

Immunoglobulin I-set domain;

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 1773401145 198 QEGQPLILTCESKGKPLPEpVLWTKDGGELPDPDRMVVSGRE----LNILFLNKTDNGTYRCEATNTIGQSSAEYVLIV 272
Cdd:pfam07679  13 QEGESARFTCTVTGTPDPE-VSWFKDGQPLRSSDRFKVTYEGgtytLTISNVQPDDSGKYTCVATNSAGEAEASAELTV 90

Second immunoglobulin (Ig)-like domain of Kirrel (kin of irregular chiasm-like) 3, and similar domains; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig)-like domain of Kirrel (kin of irregular chiasm-like) 3 (also known as Neph2). This protein has five Ig-like domains, one transmembrane domain, and a cytoplasmic tail. Included in this group is mammalian Kirrel (Neph1), Kirrel2 (Neph3), and Drosophila RST (irregular chiasm C-roughest) protein. These proteins contain multiple Ig domains, have properties of cell adhesion molecules, and are important in organ development.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145  86 PQISGfsSPVME---GDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGVAVIC 162
Cdd:cd05759     2 PVIEG--GPVISlqaGVPYNLTCRARGAKPAAEIIWFRDGEQLEGAVYSKELLKDGKRETTVSTLLITPSDLDTGRTFTC 79

                  ....*..
gi 1773401145 163 RVDHESL 169
Cdd:cd05759    80 RARNEAI 86

First (N-terminal) immunoglobulin (Ig)-like domain of nectin-like molecule 2; member of the V-set of Ig superfamily (IgSF) domains; The members here are composed of the N-terminal immunoglobulin (Ig)-like domain of nectin-like molecule-2, Necl-2 (also known as cell adhesion molecule 1 (CADM1), SynCAM1, IGSF4A, Tslc1, sgIGSF, and RA175). Nectin-like molecules have similar domain structures to those of nectins. At least five nectin-like molecules have been identified (Necl-1 - Necl-5). They all have an extracellular region containing three Ig-like domains, a transmembrane region, and a cytoplasmic region. The N-terminal Ig-like domain of the extracellular region, belongs to the V-type subfamily of Ig domains, is essential to cell-cell adhesion, and plays a part in the interaction with the envelope glycoprotein D of various viruses. Necl-2 has Ca(2+)-independent homophilic and heterophilic cell-cell adhesion activity. Necl-2 is expressed in a wide variety of tissues and is a putative tumour suppressor gene, which is downregulated in aggressive neuroblastoma.

                          10        20        30        40        50
                  ....*....|....*....|....*....|....*....|....*....|..
gi 1773401145  28 VKALRDNRIELVRASWHELSISVSDVSLSDEGQYTCSLFTMPVKTSKAYLTV 79
Cdd:cd05881    43 FRPLKDSRFQLVNFSSSELRVSLTNVSISDEGRYFCQLYTDPPQEAYTTITV 94

Fourth immunoglobulin domain of the Drosophila melanogaster Dscam protein, and similar domains; a member of the I-set of IgSF domains; The members here are composed of the fourth immunoglobulin domain of the Drosophila melanogaster Down syndrome cell adhesion molecule (DSCAM) protein and similar proteins. Down syndrome cell adhesion molecule (DSCAM) is a cell adhesion molecule that plays critical roles in neural development, including axon guidance and branching, axon target recognition, self-avoidance and synaptic formation. DSCAM belongs to the immunoglobulin superfamily and contributes to defects in the central nervous system in Down syndrome patients. Vertebrate DSCAMs differ from Drosophila Dscam1 in that they lack the extensive alternative splicing that occurs in the insect gene. Drosophila melanogaster Dscam has 38,016 isoforms generated by the alternative splicing of four variable exon clusters, which allows every neuron in the fly to display a distinctive set of Dscam proteins on its cell surface. Drosophila Dscam1 is a cell-surface protein that plays important roles in neural development and axon tiling of neurons. It is shown that thousands of isoforms bind themselves through specific homophilic (self-binding) interactions, a process which mediates cellular self-recognition. Drosophila Dscam2 is also alternatively spliced and plays a key role in the development of two visual system neurons, monopolar cells L1 and L2. This group is a member of the I-set Ig domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. Like the V-set Ig domains, members of the I-set have a discontinuous A strand but lack a C" strand.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 1773401145 198 QEGQPLILTCESKGKPLPEpVLWTKDGGELPDPDRM-----------VVSgrELNILFLNKTDNGTYRCEATNTIGQSS 265
Cdd:cd20956    14 QPGPSVSLKCVASGNPLPQ-ITWTLDGFPIPESPRFrvgdyvtsdgdVVS--YVNISSVRVEDGGEYTCTATNDVGSVS 89

Fourth immunoglobulin (Ig)-like domain of hemolin, and similar domains; a member of the I-set of IgSF domains; The members here are composed of the fourth immunoglobulin (Ig)-like domain of hemolin and similar proteins. Hemolin, an insect immunoglobulin superfamily (IgSF) member containing four Ig-like domains, is a lipopolysaccharide-binding immune protein induced during bacterial infection. Hemolin shares significant sequence similarity with the first four Ig-like domains of the transmembrane cell adhesion molecules (CAMs) of the L1 family. IgSF domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. The fourth Ig-like domain of hemolin is a member of the I-set Ig domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. Like the V-set domains, members of the I-set have a discontinuous A strand but lack a C" strand. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the muscle proteins titin, telokin, and twitchin, the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D that is involved in axonal guidance, immune function and angiogenesis.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 1773401145 198 QEGQPLILTCESKGKPLPEpVLWTKDGGEL--PDPDRMVVSGReLNILFLNKTDNGTYRCEATNTIGQSSAEYVLIV 272
Cdd:cd20978    14 KGGQDVTLPCQVTGVPQPK-ITWLHNGKPLqgPMERATVEDGT-LTIINVQPEDTGYYGCVATNEIGDIYTETLLHV 88

Immunoglobulin domain; This domain contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145 189 KIIPSTPFPQEGQPLILTCESKGKPLPEpVLWTKDGGELPdpdrmvvSGRELNILFLNKTDNGTYRCEATNTIGQSSAEY 268
Cdd:pfam13895   3 VLTPSPTVVTEGEPVTLTCSAPGNPPPS-YTWYKDGSAIS-------SSPNFFTLSVSAEDSGTYTCVARNGRGGKVSNP 74

                  ....
gi 1773401145 269 VLIV 272
Cdd:pfam13895  75 VELT 78

Immunoglobulin (Ig)-like domain of human carcinoembryonic antigen (CEA) related cell adhesion molecule (CEACAM) domains 2, 4, and 6, and similar domains; The members here are composed of the second, fourth, and sixth immunoglobulin (Ig)-like domains in human carcinoembryonic antigen (CEA) related cell adhesion molecule (CEACAM) protein subfamily. The CEA family is a group of anchored or secreted glycoproteins expressed by epithelial cells, leukocytes, endothelial cells, and placenta. The CEA family is divided into the CEACAM and pregnancy-specific glycoprotein (PSG) subfamilies. This group represents the CEACAM subfamily. CEACAM1 has many important cellular functions; it is a cell adhesion molecule and a signaling molecule that regulates the growth of tumor cells, an angiogenic factor, and a receptor for bacterial and viral pathogens, including mouse hepatitis virus (MHV). In mice, four isoforms of CEACAM1 generated by alternative splicing have either two [D1, D4] or four [D1-D4] Ig-like domains on the cell surface.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145 186 PSVKIIPSTPFpQEGQPLILTCESKGkpLPEPVLWTKDGGELPDPDRMVVSG--RELNILFLNKTDNGTYRCEATNTIGQ 263
Cdd:cd05740     2 PFISSNNSNPV-EDKDAVTLTCEPET--QNTSYLWWFNGQSLPVTPRLTLSNgnRTLTLLNVTREDAGAYQCEISNPVSA 78

                  ....*.
gi 1773401145 264 SSAEYV 269
Cdd:cd05740    79 NRSDPV 84

Fourth Ig-like domain from smooth muscle myosin light chain kinase and similar domains ; a member of the I-set of IgSF domains; The members here are composed of the fourth immunoglobulin (Ig)-like domain from smooth muscle myosin light chain kinase (MYLK) and similar domains. The Ig superfamily (IgSF) is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. IgSF domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. Unlike the V-set, one of the distinctive features of I-set domains is the lack of a C" strand. The structure of this group shows that the fourth Ig-like domain from myosin light chain kinase lacks this strand and thus belongs to the I-set of the IgSF. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the hemolymph protein hemolin, the muscle proteins titin, telokin, and twitchin, the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D that is involved in axonal guidance, immune function and angiogenesis.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145 186 PSVKIIPSTPFPQEGQPLILTCESKGKPLPEpVLWTKDGGELP-DPDRMVVSGR--ELNILFLNKTDNGTYRCEATNTIG 262
Cdd:cd20976     2 PSFSSVPKDLEAVEGQDFVAQCSARGKPVPR-ITWIRNAQPLQyAADRSTCEAGvgELHIQDVLPEDHGTYTCLAKNAAG 80

                  ....
gi 1773401145 263 QSSA 266
Cdd:cd20976    81 QVSC 84

Fourth Ig domain of the neural cell adhesion molecule contactin-2, and similar domains; The members here are composed of the fourth Ig domain of the neural cell adhesion molecule contactin-2. Contactins are comprised of six Ig domains followed by four fibronectin type III (FnIII) domains anchored to the membrane by glycosylphosphatidylinositol. Contactin-2 (also called TAG-1, axonin-1) facilitates cell adhesion by homophilic binding between molecules in apposed membranes. The first four Ig domains form the intermolecular binding fragment which arranges as a compact U-shaped module by contacts between Ig domains 1 and 4, and domains 2 and 3. It has been proposed that a linear zipper-like array forms, from contactin-2 molecules alternatively provided by the two apposed membranes.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145 200 GQPLILTCESKGKPLPEpVLWTKDGGELPDPDRMVVSGRELNILFLNKTDNGTYRCEATNTIGQ--SSAE 267
Cdd:cd05728    14 GSSLRWECKASGNPRPA-YRWLKNGQPLASENRIEVEAGDLRITKLSLSDSGMYQCVAENKHGTiyASAE 82

Fourth immunoglobulin (Ig)-like domain of peroxidasin; The members here are composed of the fourth immunoglobulin (Ig)-like domain in peroxidasin. Peroxidasin has a peroxidase domain and interacting extracellular motifs containing four Ig-like domains. It has been suggested that peroxidasin is secreted, and has functions related to the stabilization of the extracellular matrix. It may play a part in various other important processes such as removal and destruction of cells which have undergone programmed cell death and protection of the organism against non-self.

                          10        20        30        40        50        60
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 1773401145 205 LTCESKGKPLPEpVLWTKDGGELPDPDRMVVSGR-ELNILFLNKTDNGTYRCEATNTIGQSSAEYVL 270
Cdd:cd05746     3 IPCSAQGDPEPT-ITWNKDGVQVTESGKFHISPEgYLAIRDVGVADQGRYECVARNTIGYASVSMVL 68

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 1773401145  85 KPQISGFSSP--VMEGDLMQLTCKTSGSkPAADIRWFKNDKEIKDVKYLK-EEDANRKTFTVSStldfrVDRSDDGV 158
Cdd:pfam13927   1 KPVITVSPSSvtVREGETVTLTCEATGS-PPPTITWYKNGEPISSGSTRSrSLSGSNSTLTISN-----VTRSDAGT 71

Second immunoglobulin (Ig) domain of Nectin-2 and Nectin-like protein 5, and similar domains; member of the C1-set of the Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig) domain of nectin-2 (also known as poliovirus receptor related protein 2 or Cluster of Differentiation 112 (CD112)), nectin-like protein 5 (CD155), and similar proteins. Nectins and Nectin-like molecules are a family of Ca(2+)-independent immunoglobulin-like transmembrane glycoproteins belonging to the class of adhesion receptors, consisting of nine members (nectins 1 through 4 and nectin-like proteins 1 through 5). Nectins are synaptic cell adhesion molecules (CAMs) which facilitate adhesion and signaling at various intracellular junctions. Nectins form homophilic cis-dimers, followed by homophilic and heterophilic trans-dimers involved in cell-cell adhesion. Nectin-2 and nectin-3 localize at Sertoli-spermatid junctions where they form heterophilic trans-interactions between the cells that are essential for the formation and maintenance of the junctions and for spermatid development. CD155 is the fifth member in the nectin-like molecule family, and functions as the receptor of poliovirus; therefore, CD155 is also referred to as Necl-5, or PVR. In contrast to all other family members, CD155 lacks self-adhesion capacity, yet it shares with nectins the feature to interact with other nectins. For instance, CD155 heterophilically trans-interacts with nectin-3, thereby contributing significantly to the establishment of adherens junctions between epithelial cells. This group belongs to the Constant 1 (C1)-set of IgSF domains, which has one beta-sheet that is formed by strands A-B-E-D and the other strands by G-F-C-C'.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145  86 PQISGFSSPVMEGDLMQL--TCKTSGSKPAADIRWFKNDKeiKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGVAVICR 163
Cdd:cd07703     1 PKNSAEAQEVQAGGIPVPvaRCVSANGRPPARISWSSTLN--GNANTTQVPGPDSGTVTVTSEYSLVPTPEANGKEVTCK 78

                  ....*..
gi 1773401145 164 VDHESLN 170
Cdd:cd07703    79 VEHETLE 85

Third immunoglobulin (Ig)-like domain of Neural Cell Adhesion Molecule 1 (NCAM-1); member of the I-set of IgSF domains; The members here are composed of the third immunoglobulin (Ig)-like domain of Neural Cell Adhesion Molecule (NCAM-1). NCAM plays important roles in the development and regeneration of the central nervous system, in synaptogenesis and neural migration. NCAM mediates cell-cell and cell-substratum recognition and adhesion via homophilic (NCAM-NCAM), and heterophilic (NCAM-non-NCAM), interactions. NCAM is expressed as three major isoforms having different intracellular extensions. The extracellular portion of NCAM has five N-terminal Ig-like domains and two fibronectin type III domains. The double zipper adhesion complex model for NCAM homophilic binding involves Ig1, Ig2, and Ig3. By this model, Ig1 and Ig2 mediate dimerization of NCAM molecules situated on the same cell surface (cis interactions), and Ig3 domains mediate interactions between NCAM molecules expressed on the surface of opposing cells (trans interactions) through binding to the Ig1 and Ig2 domains. The adhesive ability of NCAM is modulated by the addition of polysialic acid chains to the fifth Ig-like domain.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 1773401145 200 GQPLILTCESKGKPLPEpVLWTKDGGELPDPDRMVV---SGRELNILFLNKTDNGTYRCEATNTIGQSSAEYVLIV 272
Cdd:cd05730    18 GQSVTLACDADGFPEPT-MTWTKDGEPIESGEEKYSfneDGSEMTILDVDKLDEAEYTCIAENKAGEQEAEIHLKV 92

Immunoglobulin I-set domain of the Leucine-rich repeat and immunoglobin-like domain-containing protein 1 (Lingo-1); The members here are composed of the immunoglobulin I-set (IgI) domain of the Leucine-rich repeat and immunoglobin-like domain-containing protein 1 (Lingo-1). Human Lingo-1 is a central nervous system-specific transmembrane glycoprotein also known as LERN-1, which functions as a negative regulator of neuronal survival, axonal regeneration, and oligodendrocyte differentiation and myelination. Lingo-1 is a key component of the Nogo receptor signaling complex (RTN4R/NGFR) in RhoA activation responsible for some inhibition of axonal regeneration by myelin-associated factors. The ligand-binding ectodomain of human Lingo-1 contains a bimodular, kinked structure composed of leucine-rich repeat (LRR) and immunoglobulin (Ig)-like modules. Diseases associated with Lingo-1 include mental retardation, autosomal recessive 64 and essential tremor. The Ig superfamily (IgSF) is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. IgSF domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. Unlike the V-set, one of the distinctive features of I-set domains is the lack of a C" strand. The structure of the Lingo-1 lacks this strand and thus it belongs to the I-set of the IgSF. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the hemolymph protein hemolin, the muscle proteins titin, telokin, and twitchin, the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D that is involved in axonal guidance, immune function and angiogenesis.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....
gi 1773401145 196 FPQEGQPLILTCESKGKPlPEPVLWTKDGGEL---PDPDRM-VVSGRELNILFLNKTDNGTYRCEATNTIGQSS 265
Cdd:cd20969    13 FVDEGHTVQFVCRADGDP-PPAILWLSPRKHLvsaKSNGRLtVFPDGTLEVRYAQVQDNGTYLCIAANAGGNDS 85

Immunoglobulin domain; Members of the immunoglobulin superfamily are found in hundreds of proteins of different functions. Examples include antibodies, the giant muscle kinase titin and receptor tyrosine kinases. Immunoglobulin-like domains may be involved in protein-protein and protein-ligand interactions.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145  97 EGDLMQLTCKTSGSKPAADIRWFKNDKEIKDVkyLKEEDANRKTFTvsSTLDFRVDRSDDGVAVICRVDHESLNATPQVA 176
Cdd:pfam00047  10 EGDSATLTCSASTGSPGPDVTWSKEGGTLIES--LKVKHDNGRTTQ--SSLLISNVTKEDAGTYTCVVNNPGGSATLSTS 85

                  .
gi 1773401145 177 M 177
Cdd:pfam00047  86 L 86

Fifth immunoglobulin (Ig) domain of contactin; The members here are composed of the fifth immunoglobulin (Ig) domain of contactins. Contactins are neural cell adhesion molecules and are comprised of six Ig domains followed by four fibronectin type III (FnIII) domains anchored to the membrane by glycosylphosphatidylinositol. The first four Ig domains form the intermolecular binding fragment, which arranges as a compact U-shaped module via contacts between Ig domains 1 and 4, and between Ig domains 2 and 3. Contactin-2 (TAG-1, axonin-1) may play a part in the neuronal processes of neurite outgrowth, axon guidance and fasciculation, and neuronal migration. This group also includes contactin-1 and contactin-5. The different contactins show different expression patterns in the central nervous system. During development and in adulthood, contactin-2 is transiently expressed in subsets of central and peripheral neurons. Contactin-5 is expressed specifically in the rat postnatal nervous system, peaking at about 3 weeks postnatal, and a lack of contactin-5 (NB-2) results in an impairment of neuronal activity in the rat auditory system. Contactin-5 is highly expressed in the adult human brain in the occipital lobe and in the amygdala. Contactin-1 is differentially expressed in tumor tissues and may, through a RhoA mechanism, facilitate invasion and metastasis of human lung adenocarcinoma.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145 186 PSVKIIPStpfpQEGQPLILTCESKGKPLPEpVLWTKDGGELPDPDRM-VVSGRELNILFLNKTDNGTYRCEATNTIGQS 264
Cdd:cd04969     7 PVKKKILA----AKGGDVIIECKPKASPKPT-ISWSKGTELLTNSSRIcILPDGSLKIKNVTKSDEGKYTCFAVNFFGKA 81

                  ....*...
gi 1773401145 265 SAEYVLIV 272
Cdd:cd04969    82 NSTGSLSV 89

Third immunoglobulin domain of the Drosophila melanogaster Dscam protein, and similar domains; a member of the Constant 2 (C2)-set of IgSF domains; The members here are composed of the third immunoglobulin domain of the Drosophila melanogaster Down syndrome cell adhesion molecule (DSCAM) protein and similar proteins. Down syndrome cell adhesion molecule (DSCAM) is a cell adhesion molecule that plays critical roles in neural development, including axon guidance and branching, axon target recognition, self-avoidance and synaptic formation. DSCAM belongs to the immunoglobulin superfamily and contributes to defects in the central nervous system in Down syndrome patients. Vertebrate DSCAMs differ from Drosophila Dscam1 in that they lack the extensive alternative splicing that occurs in the insect gene. Drosophila melanogaster Dscam has 38,016 isoforms generated by the alternative splicing of four variable exon clusters, which allows every neuron in the fly to display a distinctive set of Dscam proteins on its cell surface. Drosophila Dscam1 is a cell-surface protein that plays important roles in neural development and axon tiling of neurons. It is shown that thousands of isoforms bind themselves through specific homophilic (self-binding) interactions, a process which mediates cellular self-recognition. Drosophila Dscam2 is also alternatively spliced and plays a key role in the development of two visual system neurons, monopolar cells L1 and L2. IgSF domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. This group belongs to the C2-set of IgSF domains, having A, B, and E strands in one beta-sheet and A', G, F, C, and C' in the other. Unlike other Ig domain sets, the C2-set lacks the D strand.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145 187 SVKIIPSTPFPQEGQPLILTCESKGKPLPEpVLWTKDGGELPDPDRMVVSGRE-LNILFLNKTDNGTYRCEATNTI--GQ 263
Cdd:cd20957     3 SATIDPPVQTVDFGRTAVFNCSVTGNPIHT-VLWMKDGKPLGHSSRVQILSEDvLVIPSVKREDKGMYQCFVRNDGdsAQ 81

                  ....
gi 1773401145 264 SSAE 267
Cdd:cd20957    82 ATAE 85

CH3 domain (third constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, gamma, and delta chains, and CH4 domain (fourth constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, epsilon, and mu chains; member of the C1-set of I; The members here are composed of the third and fourth immunoglobulin constant domain (IgC) of alpha, delta, gamma and alpha, epsilon, and mu heavy chains, respectively. This domain is found on the Fc fragment. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. There are two types of light chains: kappa and lambda; each is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145  86 PQISGFSSPVME---GDLMQLTCKTSGSKPAaDI--RWFKNDKEIKDVKYL--KEEDANRKTFTVSSTLdfRVDRSD--D 156
Cdd:cd05768     1 PSVYLLPPPEEElslNETVTLTCLVKGFYPE-DIfvSWLQNGEPLPSADYKttAPVPESDGSFFVYSKL--NVSTADwnS 77

                          90
                  ....*....|...
gi 1773401145 157 GVAVICRVDHESL 169
Cdd:cd05768    78 GDVFSCVVGHEAL 90

agrin-responsive first immunoglobulin-like domains (Ig1) of the MuSK ectodomain; a member of the I-set of IgSF domains; The members here are composed of the first immunoglobulin-like domains (Ig1) of the Muscle-specific kinase (MuSK). MuSK is a receptor tyrosine kinase specifically expressed in skeletal muscle, where it plays a central role in the formation and maintenance of the neuromuscular junction (NMJ). MuSK is activated by agrin, a neuron-derived heparan sulfate proteoglycan. The activation of MUSK in myotubes regulates the formation of NMJs through the regulation of different processes including the specific expression of genes in subsynaptic nuclei, the reorganization of the actin cytoskeleton and the clustering of the acetylcholine receptors (AChR) in the postsynaptic membrane. The Ig superfamily (IgSF) is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. IgSF domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. Unlike the V-set, one of the distinctive features of I-set domains is the lack of a C" strand. The structure of the MuSK lacks this strand and thus it belongs to the I-set of the IgSF. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the hemolymph protein hemolin, the muscle proteins titin, telokin, and twitchin, the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D that is involved in axonal guidance, immune function and angiogenesis.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 1773401145 199 EGQPLILTCESKGKPLPEpVLWTKDGGELPDPD---RMVVSGRELNILFLNKTDNGTYRCEATNTI-GQSSAEYVLIV 272
Cdd:cd20970    16 EGENATFMCRAEGSPEPE-ISWTRNGNLIIEFNtryIVRENGTTLTIRNIRRSDMGIYLCIASNGVpGSVEKRITLQV 92

Second immunoglobulin (Ig)-like domain of a Follistatin-related protein 5, and similar domains; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig)-like domain found in human Follistatin-related protein 5 (FSTL5) and a follistatin-like molecule encoded by the CNS-related Mahya gene. Mahya genes have been retained in certain Bilaterian branches during evolution. They are conserved in Hymenoptera and Deuterostomes, but are absent from other metazoan species such as fruit fly and nematode. Mahya proteins are secretory, with a follistatin-like domain (Kazal-type serine/threonine protease inhibitor domain and EF-hand calcium-binding domain), two Ig-like domains, and a novel C-terminal domain. Mahya may be involved in learning and memory and in processing of sensory information in Hymenoptera and vertebrates. Follistatin is a secreted, multidomain protein that binds activins with high affinity and antagonizes their signaling.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145 186 PSVKIIPSTPFPQEGQPLILTCESKGKPLPEpVLWTKDG----GELPDPDRMVVSGRELNILFLNKTDNGTYRCEATNTI 261
Cdd:cd05736     1 PVIRVYPEFQAKEPGVEASLRCHAEGIPLPR-VQWLKNGmdinPKLSKQLTLIANGSELHISNVRYEDTGAYTCIAKNEG 79

                          90
                  ....*....|...
gi 1773401145 262 GQSSAEYVLIVHD 274
Cdd:cd05736    80 GVDEDISSLFVED 92

Signal-regulatory protein (SIRP) immunoglobulin-like domain 2; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig)-like domain in Signal-Regulatory Protein (SIRP), domain 2 (C1 repeat 1). The SIRPs belong to the "paired receptors" class of membrane proteins that comprise several genes coding for proteins with similar extracellular regions, but very different transmembrane/cytoplasmic regions with different (activating or inhibitory) signaling potentials. They are commonly on NK cells, but are also on many myeloid cells. Their extracellular region contains three Immunoglobulin superfamily domains, a single V-set and two C1-set IgSF domains. Their cytoplasmic tails contain either ITIMs or transmembrane regions that have positively charged residues that allow an association with adaptor proteins, such as DAP12/KARAP, containing ITAMs. There are 3 distinct SIRP members: alpha, beta, and gamma. SIRP alpha (also known as CD172a or SRC homology 2 domain-containing protein tyrosine phosphatase substrate 1/Shps-1) is a membrane receptor that interacts with a ligand CD47 expressed on many cells and gives an inhibitory signal through immunoreceptor tyrosine-based inhibition motifs in the cytoplasmic region that interact with phosphatases SHP-1 and SHP-2. SIRP beta has a short cytoplasmic region and associates with a transmembrane adapter protein DAP12 containing immunoreceptor tyrosine-based activation motifs to give an activating signal. SIRP gamma contains a very short cytoplasmic region lacking obvious signaling motifs, but also binds CD47, but with much less affinity.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1773401145  83 PEKPQISGFSSPVMEGDLMQLTCKTSGSKPAaDI--RWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGVAV 160
Cdd:cd05772     2 PSQPLVSGPSGRATPGQTVSFTCKSHGFSPR-DItlKWFKNGNELSALQTTVFPEGDSVSYSVSSTVQVVLTKDDVHSQL 80

                          90
                  ....*....|..
gi 1773401145 161 ICRVDHESLNAT 172
Cdd:cd05772    81 TCEVAHVTLQAP 92

Immunoglobulin (Ig)-like domain of titin and similar proteins; The members here are composed of the immunoglobulin (Ig)-like domain found in titin-like proteins and similar proteins. Titin (also called connectin) is a fibrous sarcomeric protein specifically found in vertebrate striated muscle. Titin is a giant protein; depending on isoform composition, it ranges from 2970 to 3700 kDa, and is of a length that spans half a sarcomere. Titin largely consists of multiple repeats of Ig-like and fibronectin type 3 (FN-III)-like domains. Titin connects the ends of myosin thick filaments to Z disks and extends along the thick filament to the H zone. It appears to function similarly to an elastic band, keeping the myosin filaments centered in the sarcomere during muscle contraction or stretching. Within the sarcomere, titin is also attached to or is associated with myosin binding protein C (MyBP-C). MyBP-C appears to contribute to the generation of passive tension by titin and like titin has repeated Ig-like and FN-III domains. Also included in this group are worm twitchin and insect projectin, thick filament proteins of invertebrate muscle which also have repeated Ig-like and FN-III domains.

                          10        20        30        40        50        60
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 1773401145 210 KGKPLPEpVLWTKDGGELPDPDR-MVVSGRELNILFL---NKTDNGTYRCEATNTIGQSSAEYVLIV 272
Cdd:cd05748    17 KGRPTPT-VTWSKDGQPLKETGRvQIETTASSTSLVIknaKRSDSGKYTLTLKNSAGEKSATINVKV 82

Immunoglobulin domain; The members here are composed of the immunoglobulin (Ig) domain found in the Ig superfamily. The Ig superfamily is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. Members of this group are components of immunoglobulin, neuroglia, cell surface glycoproteins, including T-cell receptors, CD2, CD4, CD8, and membrane glycoproteins, including butyrophilin and chondroitin sulfate proteoglycan core protein. A predominant feature of most Ig domains is a disulfide bridge connecting the two beta-sheets with a tryptophan residue packed against the disulfide bond. Ig superfamily (IgSF) domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. Typically, the V-set domains have A, B, E, and D strands in one sheet and A', G, F, C, C' and C" in the other. The structures in C1-set are smaller than those in the V-set; they have one beta sheet that is formed by strands A, B, E, and D and the other by strands G, F, C, and C'. Moreover, a C1-set Ig domain contains a short C' strand (three residues) and lacks A' and C" strand. Unlike other Ig domain sets, C2-set structures do not have a D strand. Like the V-set Ig domains, members of the I-set have a discontinuous A strand, but lack a C" strand.