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 114052913 120 VLGVPEKPQISGFSSPVMEGDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGV 199
Cdd:cd05884    1 VLGVPEKPQISGFTSPVMEGDHIQLTCKTSGSKPAADIRWFKNDKEVKDVKYLKAEDANRKTFTVSSSLDFHVDRDDDGV 80

                         90       100
                 ....*....|....*....|....
gi 114052913 200 AVICRVDHESLNATPQVAMQVLEI 223
Cdd:cd05884   81 AITCRVDHESLTATPQIAMQVLEI 104

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 114052913  227 PSVKIIPSTPFPQEGQALTLTCESKGKPLPEpVLWTKDGAELPD----PDRMVVSGRELNILFLNKTDNGTYRCEATN 300
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 114052913 120 VLGVPEKPQISGFSSPVMEGDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGV 199
Cdd:cd05884    1 VLGVPEKPQISGFTSPVMEGDHIQLTCKTSGSKPAADIRWFKNDKEVKDVKYLKAEDANRKTFTVSSSLDFHVDRDDDGV 80

                         90       100
                 ....*....|....*....|....
gi 114052913 200 AVICRVDHESLNATPQVAMQVLEI 223
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 114052913  144 LTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGVAVICRVDHESL 210
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 114052913 241 GQALTLTCESKGKPLPEpVLWTKDGAELPDPDRMVVSGRELNILFLNKTDNGTYRCEATNTIGQSSAEYVLIV 313
Cdd:cd05725   12 DDSAEFQCEVGGDPVPT-VRWRKEDGELPKGRYEILDDHSLKIRKVTAGDMGSYTCVAENMVGKIEASATLTV 83

Immunoglobulin like; IG domains that cannot be classified into one of IGv1, IGc1, IGc2, IG.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 114052913    30 QNVTVVEGGTAILTCRVDQNDNTSLQWSNPAQQTLYFDDKKALRDNrielvrASWHELSIsvSDVSLSDEGQYTCSL-FT 108
Cdd:smart00410   2 PSVTVKEGESVTLSCEASGSPPPEVTWYKQGGKLLAESGRFSVSRS------GSTSTLTI--SNVTPEDSGTYTCAAtNS 73

                           90
                   ....*....|..
gi 114052913   109 MPVKTSKAYLTV 120
Cdd:smart00410  74 SGSASSGTTLTV 85

putative band 4.1 homologues' binding motif;

                           10
                   ....*....|....*....
gi 114052913   348 LGRYLARHKGTYLTNEAKG 366
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 114052913 120 VLGVPEKPQISGFSSPVMEGDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGV 199
Cdd:cd05884    1 VLGVPEKPQISGFTSPVMEGDHIQLTCKTSGSKPAADIRWFKNDKEVKDVKYLKAEDANRKTFTVSSSLDFHVDRDDDGV 80

                         90       100
                 ....*....|....*....|....
gi 114052913 200 AVICRVDHESLNATPQVAMQVLEI 223
Cdd:cd05884   81 AITCRVDHESLTATPQIAMQVLEI 104

Second immunoglobulin (Ig)-like domain of the nectin-like molecules Necl-1 - Necl-4; member of the I-set of Ig superfamily domains; The members here are composed of the second immunoglobulin (Ig)-like domain of the nectin-like molecules Necl-1 (also known as cell adhesion molecule 3 or CADM3), Necl-2 (also known as CADM1), Necl-3 (also known as CADM2) and Necl-4 (also known as CADM4). 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. 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. Necl-4 is expressed on Schwann cells, and plays a key part in initiating peripheral nervous system (PNS) myelination. 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 114052913 121 LGVPEKPQISGFSSPVMEGDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDaNRKTFTVSSTLDFRVDRSDDGVA 200
Cdd:cd05761    1 LGVPEKPVITGFTSPVVEGDEITLTCTTSGSKPAADIRWFKNDKELKGVKEVQESG-AGKTFTVTSTLRFRVDRDDDGVA 79

                         90       100
                 ....*....|....*....|...
gi 114052913 201 VICRVDHESLNATPQVAMQVLEI 223
Cdd:cd05761   80 VICRVDHESLTSTPKQTQQVLEV 102

First (N-terminal) immunoglobulin (Ig)-like domain of nectin-like molecule-1 (Necl-1); 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-1, Necl-1 (also known as celll adhesion molecule 3 (CADM3), SynCAM2, or IGSF4). 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-1 has 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.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 114052913  27 PLTQNVTVVEGGTAILTCRVDQNDNTSLQWSNPAQQTLYFDDKKALRDNRIELVRASWHELSISVSDVSLSDEGQYTCSL 106
Cdd:cd05882    2 PVTQDETVAVGGTVTLKCGVKEHDNSSLQWSNTAQQTLYFGEKRALRDNRIQLVKSTPTELIISISNVQLSDEGEYTCSI 81

                         90
                 ....*....|....
gi 114052913 107 FTMPVKTSKAYLTV 120
Cdd:cd05882   82 FTMPVRTAKATVTV 95

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        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 114052913  28 LTQNVTVVEGGTAILTCRVDQNDNTSLQWSNPAQQTLYFDDKKALRDNRIELVRASWHELSISVSDVSLSDEGQYTCSLF 107
Cdd:cd05881    2 VTEDVTVVEGEVATISCRVKNSDDSVIQLLNPNRQTIYFRDFRPLKDSRFQLVNFSSSELRVSLTNVSISDEGRYFCQLY 81

                         90
                 ....*....|...
gi 114052913 108 TMPVKTSKAYLTV 120
Cdd:cd05881   82 TDPPQEAYTTITV 94

Second immunoglobulin (Ig)-like domain of nectin-like molecule 2 (Necl-2); 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 2 (Necl-2; also known as cell adhesion molecule 1 (CADM1)). Nectin-like molecules (Necls) 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-2 has Ca(2+)-independent homophilic and heterophilic cell-cell adhesion activity. Necl-1 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 114052913 124 PEKPQISGFSSPVMEGDLMQLTCKTSGSKPAADIRWFKNDKEIKdVKYLKEEDANRkTFTVSSTLDFRVDRSDDGVAVIC 203
Cdd:cd05883    4 PRNLVIDIQKDTAVEGEEIELNCTAMASKPAATIRWFKGNKELT-GKSEVEEWYSR-MFTVTSQLMLKVTKEDDGVPVIC 81

                 ....
gi 114052913 204 RVDH 207
Cdd:cd05883   82 LVDH 85

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 114052913  227 PSVKIIPSTPFPQEGQALTLTCESKGKPLPEpVLWTKDGAELPD----PDRMVVSGRELNILFLNKTDNGTYRCEATN 300
Cdd:pfam13927   2 PVITVSPSSVTVREGETVTLTCEATGSPPPT-ITWYKNGEPISSgstrSRSLSGSNSTLTISNVTRSDAGTYTCVASN 78

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 114052913 241 GQALTLTCESKGKPLPEpVLWTKDGAELPDPDRMVVSGRELNILFLNKTDNGTYRCEATNTIGQSSAEYVLIV 313
Cdd:cd05725   12 DDSAEFQCEVGGDPVPT-VRWRKEDGELPKGRYEILDDHSLKIRKVTAGDMGSYTCVAENMVGKIEASATLTV 83

Immunoglobulin like; IG domains that cannot be classified into one of IGv1, IGc1, IGc2, IG.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 114052913    30 QNVTVVEGGTAILTCRVDQNDNTSLQWSNPAQQTLYFDDKKALRDNrielvrASWHELSIsvSDVSLSDEGQYTCSL-FT 108
Cdd:smart00410   2 PSVTVKEGESVTLSCEASGSPPPEVTWYKQGGKLLAESGRFSVSRS------GSTSTLTI--SNVTPEDSGTYTCAAtNS 73

                           90
                   ....*....|..
gi 114052913   109 MPVKTSKAYLTV 120
Cdd:smart00410  74 SGSASSGTTLTV 85

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 114052913 127 PQISGfsSPVME---GDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDDGVAVIC 203
Cdd:cd05759    2 PVIEG--GPVISlqaGVPYNLTCRARGAKPAAEIIWFRDGEQLEGAVYSKELLKDGKRETTVSTLLITPSDLDTGRTFTC 79

                 ....*..
gi 114052913 204 RVDHESL 210
Cdd:cd05759   80 RARNEAI 86

Third immunoglobulin (Ig)-like domain of peroxidasin; The members here are composed of the third 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        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 114052913 240 EGQALTLTCESKGKPLPePVLWTKDGAELP-DPDRMVVSGRELNILFLNKTDNGTYRCEATNTIGQSSAEYVLIV 313
Cdd:cd05745    1 EGQTVDFLCEAQGYPQP-VIAWTKGGSQLSvDRRHLVLSSGTLRISRVALHDQGQYECQAVNIVGSQRTVAQLTV 74

Immunoglobulin (Ig)-like I-set domain of Neural Cell Adhesion Molecule 1 (NCAM-1) and similar proteins; The members here are composed of the fourth 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. Also included in this group is NCAM-2 (also known as OCAM/mamFas II and RNCAM) NCAM-2 is differentially expressed in the developing and mature olfactory epithelium (OE). One of the unique features of I-set domains is the lack of a C" strand. The structures of this group show that the Ig domain lacks this strand and thus is a member of the I-set of Ig domains.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 114052913 240 EGQALTLTCESKGKPLPEpVLWTK--DG--AELPDPD-RMVVSGR----ELNILFLNKTDNGTYRCEATNTIGQSS 306
Cdd:cd05732   15 ELEQITLTCEAEGDPIPE-ITWRRatRGisFEEGDLDgRIVVRGHarvsSLTLKDVQLTDAGRYDCEASNRIGGDQ 89

Immunoglobulin domain; This domain contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 114052913  230 KIIPSTPFPQEGQALTLTCESKGKPLPEpVLWTKDGAELPdpdrmvvSGRELNILFLNKTDNGTYRCEATNTIGQSSAEY 309
Cdd:pfam13895   3 VLTPSPTVVTEGEPVTLTCSAPGNPPPS-YTWYKDGSAIS-------SSPNFFTLSVSAEDSGTYTCVARNGRGGKVSNP 74

                  ....
gi 114052913  310 VLIV 313
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 114052913 227 PSVKIIPSTPFpQEGQALTLTCESKGkpLPEPVLWTKDGAELPDPDRMVVSG--RELNILFLNKTDNGTYRCEATNTIGQ 304
Cdd:cd05740    2 PFISSNNSNPV-EDKDAVTLTCEPET--QNTSYLWWFNGQSLPVTPRLTLSNgnRTLTLLNVTREDAGAYQCEISNPVSA 78

                 ....*.
gi 114052913 305 SSAEYV 310
Cdd:cd05740   79 NRSDPV 84

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 114052913 241 GQALTLTCESKGKPLPEpVLWTKDGAELPDPDRMVV---SGRELNILFLNKTDNGTYRCEATNTIGQSSAEYVLIV 313
Cdd:cd05730   18 GQSVTLACDADGFPEPT-MTWTKDGEPIESGEEKYSfneDGSEMTILDVDKLDEAEYTCIAENKAGEQEAEIHLKV 92

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 114052913 241 GQALTLTCESKGKPLPEpVLWTKDGAELPDPDRMVVSGRELNILFLNKTDNGTYRCEATNTIGQ--SSAE 308
Cdd:cd05728   14 GSSLRWECKASGNPRPA-YRWLKNGQPLASENRIEVEAGDLRITKLSLSDSGMYQCVAENKHGTiyASAE 82

Second 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 second 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 the 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, and 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, 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 Slit-2 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 114052913 241 GQALTLTCES-KGKPLPEpVLWTKDGAELPDPD--RMVVSGRELNILFLNKTDNGTYRCEATNTIG--QSSAEYVLI 312
Cdd:cd05724   12 GEMAVLECSPpRGHPEPT-VSWRKDGQPLNLDNerVRIVDDGNLLIAEARKSDEGTYKCVATNMVGerESRAARLSV 87

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 114052913 246 LTCESKGKPLPEpVLWTKDGAELPDPDRMVVSGR-ELNILFLNKTDNGTYRCEATNTIGQSSAEYVL 311
Cdd:cd05746    3 IPCSAQGDPEPT-ITWNKDGVQVTESGKFHISPEgYLAIRDVGVADQGRYECVARNTIGYASVSMVL 68

Third immunoglobulin domain in Cluster of Differentiation (CD) 22; member of the Constant 2 (C2)-set of IgSF domains; The members here are composed of the third immunoglobulin domain in Cluster of Differentiation (CD) 22 (also known as Siglec-2). CD22, a sialic-acid binding immunoglobulin type-lectin (Siglec) family member, is an inhibitory co-receptor of the B-cell receptor (BCR). The inhibitory function of CD22 and its restricted expression on B cells makes CD22 an attractive target against dysregulated B cells that cause autoimmune diseases and B-cell-derived cancers. CD22 plays a vital role in establishing a baseline level of B-cell inhibition, and thus is an important determinant of homeostasis in humoral immunity. Siglecs are primarily expressed on immune cells and recognize sialic acid-containing glycan ligands. Siglecs are organized as an extracellular module composed of Ig-like domains (an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains), followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG (Siglec-4, myelin-associated glycoprotein), the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11. 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' in the other. Unlike other Ig domain sets, the C2-set lacks the D strand.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 114052913 229 VKIIPSTPFPQEGQALTLTCE-SKGKPLPEPVLWTKDGAELPDPDRMVvsgreLNILFLNKTDNGTYRCEATNTIG-QSS 306
Cdd:cd20937    5 IKVTPSDAIVREGDSVTMTCEvSSSNPEYTTVSWLKDGTSLKKQNTFT-----LNLREVTKDQSGKYCCQVSNDVGpGRS 79

                 ....*...
gi 114052913 307 AEYVLIVH 314
Cdd:cd20937   80 EEVFLQVQ 87

Immunoglobulin constant (IgC)-like domain of antigen receptor Cluster of Differentiation (CD) 80; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin constant (IgC)-like domain of the antigen receptor Cluster of Differentiation (CD) 80. CD80 (also known as glycoprotein B7-1) and CD86 (also known as glycoprotein B7-2) are expressed on antigen-presenting cells and deliver the co-stimulatory signal through CD28 and CTLA-4 (CD152) on T cells. signaling through CD28 augments the T-cell response, whereas CTLA-4 signaling attenuates it. CD80 contains two Ig-like domains, an amino-terminal immunoglobulin variable (IgV)-like domain characteristic of adhesion molecules, and a membrane proximal immunoglobulin constant (IgC)-like domain similar to the constant domains of antigen receptors. Members of the Ig family are components of immunoglobulin, T-cell receptors, CD1 cell surface glycoproteins, secretory glycoproteins A/C, and major histocompatibility complex (MHC) class I/II molecules. In immunoglobulins, each chain is composed of one variable domain (IgV) and one or more IgC domains. These names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. The IgV domain is responsible for antigen binding, and the IgC domain is involved in oligomerization and molecular interactions.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 114052913 127 PQISGFSSPVmeGDLMQLTCKTSGSKPAADIRWFKNDKEIKDVKYLKEEDANRKTFTVSSTLDFRVDRSDdgvAVICRV 205
Cdd:cd16083    4 PSITEFGNPS--PNIKRIICSTSGGFPEPRLSWLENGEELNAINTTVSQDPETELYTVSSELDFNVTYNH---SIVCLI 77

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 114052913  126 KPQISGFSSP--VMEGDLMQLTCKTSGSkPAADIRWFKNDKEIKDVKYLK-EEDANRKTFTVSStldfrVDRSDDGV 199
Cdd:pfam13927   1 KPVITVSPSSvtVREGETVTLTCEATGS-PPPTITWYKNGEPISSGSTRSrSLSGSNSTLTISN-----VTRSDAGT 71

Second Ig-like domain of the giant muscle protein titin Z1z2 in the sarcomeric Z-disk, and similar domains; a member of the I-set of IgSF domains; The members here are composed of the second immunoglobulin (Ig)-like domain of the giant muscle protein titin Z1z2 in the sarcomeric Z-disk and similar proteins. Titin is a key component in the assembly and functioning of vertebrate striated muscles. By providing connections at the level of individual microfilaments, it contributes to the fine balance of forces between the two halves of the sarcomere. 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 titin Z1z2 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 114052913 240 EGQALTLTCESKGKPLPEpVLWTKDGAELPD-PDRMVVSGRELNILFLNKT---DNGTYRCEATNTIGQ--SSAE 308
Cdd:cd20972   15 EGSKVRLECRVTGNPTPV-VRWFCEGKELQNsPDIQIHQEGDLHSLIIAEAfeeDTGRYSCLATNSVGSdtTSAE 88

Immunoglobulin (Ig)-like I-set domain of Neural Cell Adhesion Molecule 2 (NCAM-2); The members here are composed of the fourth Ig domain of Neural Cell Adhesion Molecule NCAM-2 (also known as OCAM/mamFas II and RNCAM). NCAM-2 is organized similarly to NCAM, including five N-terminal Ig-like domains and two fibronectin type III domains. NCAM-2 is differentially expressed in the developing and mature olfactory epithelium (OE), and may function like NCAM, as an adhesion molecule. One of the unique features of I-set domains is the lack of a C" strand. The structures of this group show that the Ig domain lacks this strand and thus is a member of the I-set of Ig domains.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 114052913  23 QGQFPLTQNVTVVEGGTAILTCRVDQNDNTSLQWSNPAQQTLYFDDKKALrDNRIElVRASWHELSISVSDVSLSDEGQY 102
Cdd:cd05870    2 QPHIIQLKNETTVENGAATLSCKAEGEPIPEITWKRASDGHTFSEGDKSP-DGRIE-VKGQHGESSLHIKDVKLSDSGRY 79

                 ..
gi 114052913 103 TC 104
Cdd:cd05870   80 DC 81

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 114052913 240 EGQALTLTCESKGKPLPEpVLWTKDGAELPDPD---RMVVSGRELNILFLNKTDNGTYRCEATNTI-GQSSAEYVLIV 313
Cdd:cd20970   16 EGENATFMCRAEGSPEPE-ISWTRNGNLIIEFNtryIVRENGTTLTIRNIRRSDMGIYLCIASNGVpGSVEKRITLQV 92

Third immunoglobulin (Ig)-like domain of the L1 cell adhesion molecule (CAM); The members here are composed of the third immunoglobulin (Ig)-like domain of the L1 cell adhesion molecule (CAM). L1 belongs to the L1 subfamily of cell adhesion molecules (CAMs) and is comprised of an extracellular region having six Ig-like domains, five fibronectin type III domains, a transmembrane region and an intracellular domain. L1 is primarily expressed in the nervous system and is involved in its development and function. L1 is associated with an X-linked recessive disorder, X-linked hydrocephalus, MASA syndrome, or spastic paraplegia type 1, that involves abnormalities of axonal growth. This group also contains the chicken neuron-glia cell adhesion molecule, Ng-CAM.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 114052913 240 EGQALTLTCESKGKPLPEpVLWTK-DGAELPDPDRMVVSGRELNILFLNKTDNGTYRCEATNTIGQSSAEYVLIV 313
Cdd:cd05876    9 RGQSLVLECIAEGLPTPT-VKWLRpSGPLPPDRVKYQNHNKTLQLLNVGESDDGEYVCLAENSLGSARHAYYVTV 82

Immunoglobulin (Ig)-like I-set domain of Neural Cell Adhesion Molecule 2 (NCAM-2); The members here are composed of the fourth Ig domain of Neural Cell Adhesion Molecule NCAM-2 (also known as OCAM/mamFas II and RNCAM). NCAM-2 is organized similarly to NCAM, including five N-terminal Ig-like domains and two fibronectin type III domains. NCAM-2 is differentially expressed in the developing and mature olfactory epithelium (OE), and may function like NCAM, as an adhesion molecule. One of the unique features of I-set domains is the lack of a C" strand. The structures of this group show that the Ig domain lacks this strand and thus is a member of the I-set of Ig domains.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 114052913 240 EGQALTLTCESKGKPLPEpVLWTK--DGAELPDPD-----RMVVSGR----ELNILFLNKTDNGTYRCEATNTIG 303
Cdd:cd05870   15 ENGAATLSCKAEGEPIPE-ITWKRasDGHTFSEGDkspdgRIEVKGQhgesSLHIKDVKLSDSGRYDCEAASRIG 88

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 114052913 127 PQISGFSSPVME---GDLMQLTCKTSGSKPAaDI--RWFKNDKEIKDVKYL--KEEDANRKTFTVSSTLdfRVDRSD--D 197
Cdd:cd05768    1 PSVYLLPPPEEElslNETVTLTCLVKGFYPE-DIfvSWLQNGEPLPSADYKttAPVPESDGSFFVYSKL--NVSTADwnS 77

                         90
                 ....*....|...
gi 114052913 198 GVAVICRVDHESL 210
Cdd:cd05768   78 GDVFSCVVGHEAL 90

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 114052913 228 SVKIIPSTPFPQEGQALTLTCESKGKPLPEpVLWTKDGAELPDPDRMVVSGRE-LNILFLNKTDNGTYRCEATNTI--GQ 304
Cdd:cd20957    3 SATIDPPVQTVDFGRTAVFNCSVTGNPIHT-VLWMKDGKPLGHSSRVQILSEDvLVIPSVKREDKGMYQCFVRNDGdsAQ 81

                 ....
gi 114052913 305 SSAE 308
Cdd:cd20957   82 ATAE 85

Third immunoglobulin (Ig)-like domain of the receptor protein tyrosine phosphatase (RPTP)-F (also known as LAR), type IIa; member of the I-set of IgSF domains; The members here are composed of the third immunoglobulin (Ig)-like domain found in the receptor protein tyrosine phosphatase (RPTP)-F, also known as LAR. LAR belongs to the RPTP type IIa subfamily. Members of this subfamily are cell adhesion molecule-like proteins involved in central nervous system (CNS) development. They have large extracellular portions comprised of multiple Ig-like domains and two to nine fibronectin type III (FNIII) domains and a cytoplasmic portion having two tandem phosphatase domains. Included in this group is Drosophila LAR (DLAR).

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 114052913 231 IIPSTPFPQEGQALTLTCESKGKPLPEpVLWTKDGAELPDPDRMVVsGRelNILFL-NKTDNGTYRCEATNTIGQSSAEY 309
Cdd:cd05739    2 IPPSNHEVMPGGSVNLTCVAVGAPMPY-VKWMKGGEELTKEDEMPV-GR--NVLELtNIYESANYTCVAISSLGMIEATA 77