Src Homology 3 domain superfamily; Src Homology 3 (SH3) domains are protein interaction domains that bind proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. Thus, they are referred to as proline-recognition domains (PRDs). SH3 domains are less selective and show more diverse specificity compared to other PRDs. They have been shown to bind peptide sequences that lack the PxxP motif; examples include the PxxDY motif of Eps8 and the RKxxYxxY sequence in SKAP55. SH3 domain containing proteins play versatile and diverse roles in the cell, including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies, among others. Many members of this superfamily are adaptor proteins that associate with a number of protein partners, facilitating complex formation and signal transduction.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....
gi 340007427  16 NQKRSLYVRAMFDYDKSKDSGLPSQGLSFKYGDILHVINASDDEWWQARRVTLDGDSEEMGVIPSKRRVERKER 89
Cdd:cd12032    1 NQKRSLYVRAMFDYEKSKDSGLPSQGLSFRYGDILHVINASDDEWWQARRVTPDGDSEEMGVIPSKRRVERKER 74

Guanylate kinase homologues; Active enzymes catalyze ATP-dependent phosphorylation of GMP to GDP. Structure resembles that of adenylate kinase. So-called membrane-associated guanylate kinase homologues (MAGUKs) do not possess guanylate kinase activities; instead at least some possess protein-binding functions.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 340007427   154 KDRINDDLISEFPDKFGSCVPHTTRPKRDYEVDGRDYHFViSREQMEKDIQEHKFIEAGQYNDNLYGTSVQSVRFVAERG 233
Cdd:smart00072   5 KGTLLAELIQEIPDAFERVVSHTTRPPRPGEVNGVDYHFV-SKEEFEDDIKSGLFLEWGEYEGNYYGTSKETIRQVAEKG 83

                           90       100       110       120       130       140       150       160
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 340007427   234 KHCILDVSGNAIKRLQVAQLYPIAIFIKPKSLEPLMEMNKRLTEEQAKKTYDRAIKLEQEFGEY--FTAIVQGDTLEDIY 311
Cdd:smart00072  84 KHCLLDIDPQGVKQLRKAQLYPIVIFIAPPSSEELERRLRQRGTETSERIQKRLAAAQKEAQEYhlFDYVIVNDDLEDAY 163

                          170
                   ....*....|
gi 340007427   312 NQCKLVIEEQ 321
Cdd:smart00072 164 EELKEILEAE 173

guanylate kinase

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 340007427 142 NYTRPVIILGPM---KDRINDDLISEFPDKFGSCVPHTTRPKRDYEVDGRDYHFViSREQMEKDIQEHKFIEAGQYNDNL 218
Cdd:PLN02772 133 NAEKPIVISGPSgvgKGTLISMLMKEFPSMFGFSVSHTTRAPREMEKDGVHYHFT-ERSVMEKEIKDGKFLEFASVHGNL 211

                         90       100       110       120       130       140       150       160
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 340007427 219 YGTSVQSVRFVAERGKHCILDVSGNAIKRLQVAQLYPIAIFIKPKSLEplmEMNKRL------TEEQAKKTYDRAiKLEQ 292
Cdd:PLN02772 212 YGTSIEAVEVVTDSGKRCILDIDVQGARSVRASSLEAIFIFICPPSME---ELEKRLrargteTEEQIQKRLRNA-EAEL 287

                        170       180
                 ....*....|....*....|....*.
gi 340007427 293 EFGE---YFTAIVQGDTLEDIYNQCK 315
Cdd:PLN02772 288 EQGKssgIFDHILYNDNLEECYKNLK 313

Guanosine monophosphate kinase (GMPK, EC 2.7.4.8), also known as guanylate kinase (GKase), catalyzes the reversible phosphoryl transfer from adenosine triphosphate (ATP) to guanosine monophosphate (GMP) to yield adenosine diphosphate (ADP) and guanosine diphosphate (GDP). It plays an essential role in the biosynthesis of guanosine triphosphate (GTP). This enzyme is also important for the activation of some antiviral and anticancer agents, such as acyclovir, ganciclovir, carbovir, and thiopurines.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 340007427 146 PVIILGPM---KDRINDDLISEFPDKFGSCVPHTTRPKRDYEVDGRDYHFViSREQMEKDIQEHKFIEAGQYNDNLYGTS 222
Cdd:cd00071    1 LIVLSGPSgvgKSTLLKRLLEEFDPNFGFSVSHTTRKPRPGEVDGVDYHFV-SKEEFERLIENGEFLEWAEFHGNYYGTS 79

                         90       100       110       120
                 ....*....|....*....|....*....|....*....|
gi 340007427 223 VQSVRFVAERGKHCILDVSGNAIKRLQVAQLYPIAIFIKP 262
Cdd:cd00071   80 KAAVEEALAEGKIVILEIDVQGARQVKKSYPDAVSIFILP 119

Src homology 3 domains; Src homology 3 (SH3) domains bind to target proteins through sequences containing proline and hydrophobic amino acids. Pro-containing polypeptides may bind to SH3 domains in 2 different binding orientations.

                           10        20        30        40        50
                   ....*....|....*....|....*....|....*....|....*....|....*....
gi 340007427    22 YVRAMFDYDKSKDsglpsQGLSFKYGDILHVINASDDEWWQARRvtldgDSEEMGVIPS 80
Cdd:smart00326   4 QVRALYDYTAQDP-----DELSFKKGDIITVLEKSDDGWWKGRL-----GRGKEGLFPS 52

Guanylate kinase homologues; Active enzymes catalyze ATP-dependent phosphorylation of GMP to GDP. Structure resembles that of adenylate kinase. So-called membrane-associated guanylate kinase homologues (MAGUKs) do not possess guanylate kinase activities; instead at least some possess protein-binding functions.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 340007427   154 KDRINDDLISEFPDKFGSCVPHTTRPKRDYEVDGRDYHFViSREQMEKDIQEHKFIEAGQYNDNLYGTSVQSVRFVAERG 233
Cdd:smart00072   5 KGTLLAELIQEIPDAFERVVSHTTRPPRPGEVNGVDYHFV-SKEEFEDDIKSGLFLEWGEYEGNYYGTSKETIRQVAEKG 83

                           90       100       110       120       130       140       150       160
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 340007427   234 KHCILDVSGNAIKRLQVAQLYPIAIFIKPKSLEPLMEMNKRLTEEQAKKTYDRAIKLEQEFGEY--FTAIVQGDTLEDIY 311
Cdd:smart00072  84 KHCLLDIDPQGVKQLRKAQLYPIVIFIAPPSSEELERRLRQRGTETSERIQKRLAAAQKEAQEYhlFDYVIVNDDLEDAY 163

                          170
                   ....*....|
gi 340007427   312 NQCKLVIEEQ 321
Cdd:smart00072 164 EELKEILEAE 173

Src Homology 3 domain of Disks large homolog proteins; The DLG-like proteins are scaffolding proteins that cluster at synapses and are also called PSD (postsynaptic density)-95 proteins or SAPs (synapse-associated proteins). They play important roles in synaptic development and plasticity, cell polarity, migration and proliferation. They are members of the MAGUK (membrane-associated guanylate kinase) protein family, which is characterized by the presence of a core of three domains: PDZ, SH3, and guanylate kinase (GuK). The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. DLG-like proteins contain three PDZ domains and varying N-terminal regions. All DLG proteins exist as alternatively-spliced isoforms. Vertebrates contain four DLG proteins from different genes, called DLG1-4. DLG4 and DLG2 are found predominantly at postsynaptic sites and they mediate surface ion channel and receptor clustering. DLG3 is found axons and some presynaptic terminals. DLG1 interacts with AMPA-type glutamate receptors and is critical in their maturation and delivery to synapses. The SH3 domain of DLG4 binds and clusters the kainate subgroup of glutamate receptors via two proline-rich sequences in their C-terminal tail. It also binds AKAP79/150 (A-kinase anchoring protein). SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|.
gi 340007427  22 YVRAMFDYDKSKDSGLPSQGLSFKYGDILHVINASDDEWWQARRVTLDGDSEEMGVIPSKR 82
Cdd:cd11861    1 YVRALFDYDPSRDSGLPSQGLSFKFGDILHVTNASDDEWWQARRVTPNGEEEEVGVIPSKR 61

Src Homology 3 domain of Disks Large homolog 3; DLG3, also called synapse-associated protein 102 (SAP102), is a scaffolding protein that clusters at synapses and plays an important role in synaptic development and plasticity. Mutations in DLG3 cause midgestational embryonic lethality in mice and may be associated with nonsyndromic X-linked mental retardation in humans. It interacts with the NEDD4 (neural precursor cell-expressed developmentally downregulated 4) family of ubiquitin ligases and promotes apical tight junction formation. DLG3 is a member of the MAGUK (membrane-associated guanylate kinase) protein family, which is characterized by the presence of a core of three domains: PDZ, SH3, and guanylate kinase (GuK). The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. DLG3 contains three PDZ domains. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 340007427  19 RSLYVRAMFDYDKSKDSGLPSQGLSFKYGDILHVINASDDEWWQARRVTLDGDSEEMGVIPSKRRVE 85
Cdd:cd12029    1 RSLYVRALFDYDRTRDSCLPSQGLSFSYGDILHVINASDDEWWQARLVTPHGESEQIGVIPSKKRVE 67

Src Homology 3 domain of Disks Large homolog 4; DLG4, also called postsynaptic density-95 (PSD95) or synapse-associated protein 90 (SAP90), is a scaffolding protein that clusters at synapses and plays an important role in synaptic development and plasticity. It is responsible for the membrane clustering and retention of many transporters and receptors such as potassium channels and PMCA4b, a P-type ion transport ATPase, among others. DLG4 is a member of the MAGUK (membrane-associated guanylate kinase) protein family, which is characterized by the presence of a core of three domains: PDZ, SH3, and guanylate kinase (GuK). The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. DLG4 contains three PDZ domains. The SH3 domain of DLG4 binds and clusters the kainate subgroup of glutamate receptors via two proline-rich sequences in their C-terminal tail. It also binds AKAP79/150 (A-kinase anchoring protein). SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|....
gi 340007427  22 YVRAMFDYDKSKDSGLPSQGLSFKYGDILHVINASDDEWWQARRVTLDGDSEEMGVIPSKRRVE 85
Cdd:cd12030    3 YIRALFDYDKTKDCGFLSQALSFRFGDVLHVIDAGDEEWWQARRVHSDSETEEIGFIPSKRRVE 66

Guanosine monophosphate kinase (GMPK, EC 2.7.4.8), also known as guanylate kinase (GKase), catalyzes the reversible phosphoryl transfer from adenosine triphosphate (ATP) to guanosine monophosphate (GMP) to yield adenosine diphosphate (ADP) and guanosine diphosphate (GDP). It plays an essential role in the biosynthesis of guanosine triphosphate (GTP). This enzyme is also important for the activation of some antiviral and anticancer agents, such as acyclovir, ganciclovir, carbovir, and thiopurines.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 340007427 146 PVIILGPM---KDRINDDLISEFPDKFGSCVPHTTRPKRDYEVDGRDYHFViSREQMEKDIQEHKFIEAGQYNDNLYGTS 222
Cdd:cd00071    1 LIVLSGPSgvgKSTLLKRLLEEFDPNFGFSVSHTTRKPRPGEVDGVDYHFV-SKEEFERLIENGEFLEWAEFHGNYYGTS 79

                         90       100       110       120
                 ....*....|....*....|....*....|....*....|
gi 340007427 223 VQSVRFVAERGKHCILDVSGNAIKRLQVAQLYPIAIFIKP 262
Cdd:cd00071   80 KAAVEEALAEGKIVILEIDVQGARQVKKSYPDAVSIFILP 119

guanylate kinase; Provisional

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 340007427 173 VPHTTRPKRDYEVDGRDYHFViSREQMEKDIQEHKFIEAGQYNDNLYGTSVQSVRFVAERGKHCIL--DVSGnAikrLQV 250
Cdd:PRK00300  36 VSATTRAPRPGEVDGVDYFFV-SKEEFEEMIENGEFLEWAEVFGNYYGTPRSPVEEALAAGKDVLLeiDWQG-A---RQV 110

                         90       100
                 ....*....|....*....|....*...
gi 340007427 251 AQLYP--IAIFIKPKSLEplmEMNKRLT 276
Cdd:PRK00300 111 KKKMPdaVSIFILPPSLE---ELERRLR 135

Src Homology 3 domain of Membrane Protein, Palmitoylated 1 (or MAGUK p55 subfamily member 1)-like proteins; This subfamily includes MPP1, CASK (Calcium/calmodulin-dependent Serine protein Kinase), Caenorhabditis elegans lin-2, and similar proteins. MPP1 and CASK are scaffolding proteins from the MAGUK (membrane-associated guanylate kinase) protein family, which is characterized by the presence of a core of three domains: PDZ, SH3, and guanylate kinase (GuK). In addition, they also have the Hook (Protein 4.1 Binding) motif in between the SH3 and GuK domains. The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. CASK and lin-2 also contain an N-terminal calmodulin-dependent kinase (CaMK)-like domain and two L27 domains. MPP1 is ubiquitously-expressed and plays roles in regulating neutrophil polarity, cell shape, hair cell development, and neural development and patterning of the retina. CASK is highly expressed in the mammalian nervous system and plays roles in synaptic protein targeting, neural development, and gene expression regulation. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 340007427  22 YVRAMFDYDKSKDSGLPSQ--GLSFKYGDILHVINASDDEWWQARrvtLDGDSEEM-GVIPS 80
Cdd:cd12035    1 YVRAQFDYDPSKDDLIPCQqaGIAFKTGDILQIISKDDHNWWQAR---KPGASKEPaGLIPS 59

guanylate kinase; Provisional

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 340007427 135 PVTRQEINYTRPVIILGPM---KDRINDDLiSEFPDKFGSCVPHTTRPKRDYEVDGRDYHFViSREQMEKDIQEHKFIEA 211
Cdd:PRK14738   4 PWLFNKPAKPLLVVISGPSgvgKDAVLARM-RERKLPFHFVVTATTRPKRPGEIDGVDYHFV-TPEEFREMISQNELLEW 81

                         90       100       110       120       130       140       150
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 340007427 212 GQYNDNLYGTSVQSVRFVAERGKHCIL--DVSGNA-IKRLqVAQlyPIAIFIKPKSLEPLM-EMNKRLTE 277
Cdd:PRK14738  82 AEVYGNYYGVPKAPVRQALASGRDVIVkvDVQGAAsIKRL-VPE--AVFIFLAPPSMDELTrRLELRRTE 148

Src Homology 3 domain of Membrane Protein, Palmitoylated 1 (or MAGUK p55 subfamily member 1); MPP1, also called 55 kDa erythrocyte membrane protein (p55), is a ubiquitously-expressed scaffolding protein that plays roles in regulating neutrophil polarity, cell shape, hair cell development, and neural development and patterning of the retina. It was originally identified as an erythrocyte protein that stabilizes the actin cytoskeleton to the plasma membrane by forming a complex with 4.1R protein and glycophorin C. MPP1 is one of seven vertebrate homologs of the Drosophila Stardust protein, which is required in establishing cell polarity, and it contains the three domains characteristic of MAGUK (membrane-associated guanylate kinase) proteins: PDZ, SH3, and guanylate kinase (GuK). In addition, it also contains the Hook (Protein 4.1 Binding) motif in between the SH3 and GuK domains. The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 340007427  22 YVRAMFDYDKSKDSGLPSQ--GLSFKYGDILHVINASDDEWWQARrvtLDGDSEE-MGVIPS 80
Cdd:cd12080    1 YMRAQFDYDPKKDNLIPCKeaGLKFQTGDIIQIINKDDSNWWQGR---VEGSGEEsAGLIPS 59

Src Homology 3 domain of Calcium/calmodulin-dependent Serine protein Kinase; CASK is a scaffolding protein that is highly expressed in the mammalian nervous system and plays roles in synaptic protein targeting, neural development, and gene expression regulation. CASK interacts with many different binding partners including parkin, neurexin, syndecans, calcium channel proteins, caskin, among others, to perform specific functions in different subcellular locations. Disruption of the CASK gene in mice results in neonatal lethality while mutations in the human gene have been associated with X-linked mental retardation. Drosophila CASK is associated with both pre- and postsynaptic membranes and is crucial in synaptic transmission and vesicle cycling. CASK contains an N-terminal calmodulin-dependent kinase (CaMK)-like domain, two L27 domains, followed by the core of three domains characteristic of MAGUK (membrane-associated guanylate kinase) proteins: PDZ, SH3, and guanylate kinase (GuK). In addition, it also contains the Hook (Protein 4.1 Binding) motif in between the SH3 and GuK domains. The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|.
gi 340007427  22 YVRAMFDYDKSKDSGLPSQ--GLSFKYGDILHVINASDDEWWQARRVTLDGDseEMGVIPS 80
Cdd:cd12081    1 YVRAQFEYDPLKDDLIPCKqaGIRFRVGDILQIISKDDHNWWQAKLENSKNG--TAGLIPS 59

Src Homology 3 domain of Membrane Protein, Palmitoylated 2 (or MAGUK p55 subfamily member 2); MPP2 is a scaffolding protein that interacts with the non-receptor tyrosine kinase c-Src in epithelial cells to negatively regulate its activity and morphological function. It is one of seven vertebrate homologs of the Drosophila Stardust protein, which is required in establishing cell polarity, and it contains two L27 domains followed by the core of three domains characteristic of MAGUK (membrane-associated guanylate kinase) proteins: PDZ, SH3, and guanylate kinase (GuK). In addition, it also contains the Hook (Protein 4.1 Binding) motif in between the SH3 and GuK domains. The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 340007427  22 YVRAMFDYDKSKDSGLPSQ--GLSFKYGDILHVINASDDEWWQARRVtlDGDSEemGVIPSK 81
Cdd:cd12037    1 FVKCHFDYDPSSDSLIPCKeaGLKFRAGDLLQIVNQEDPNWWQACHV--EGGSA--GLIPSQ 58

Src Homology 3 domain of Membrane Protein, Palmitoylated 6 (or MAGUK p55 subfamily member 6); MPP6, also called Veli-associated MAGUK 1 (VAM-1) or PALS2, is a scaffolding protein that binds to Veli-1, a homolog of Caenorhabditis Lin-7. It is one of seven vertebrate homologs of the Drosophila Stardust protein, which is required in establishing cell polarity, and it contains two L27 domains followed by the core of three domains characteristic of MAGUK (membrane-associated guanylate kinase) proteins: PDZ, SH3, and guanylate kinase (GuK). In addition, it also contains the Hook (Protein 4.1 Binding) motif in between the SH3 and GuK domains. The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 340007427  22 YVRAMFDYDKSKDSGLPSQ--GLSFKYGDILHVINASDDEWWQARRVTLDGDSeemGVIPSK 81
Cdd:cd12038    1 FVKCHFDYNPYNDNLIPCKeaGLKFSKGEILQIVNREDPNWWQASHVKEGGSA---GLIPSQ 59

SH3 domain; SH3 (Src homology 3) domains are often indicative of a protein involved in signal transduction related to cytoskeletal organization. First described in the Src cytoplasmic tyrosine kinase. The structure is a partly opened beta barrel.

                          10        20        30        40        50
                  ....*....|....*....|....*....|....*....|....*....|....*..
gi 340007427   24 RAMFDYDKSKDSGLpsqglSFKYGDILHVINASDDEWWQARRvtldgDSEEMGVIPS 80
Cdd:pfam00018   1 VALYDYTAQEPDEL-----SFKKGDIIIVLEKSEDGWWKGRN-----KGGKEGLIPS 47

Src homology 3 domain of Src kinase-like Protein Tyrosine Kinases; Src subfamily members include Src, Lck, Hck, Blk, Lyn, Fgr, Fyn, Yrk, Yes, and Brk. Src (or c-Src) proteins are cytoplasmic (or non-receptor) PTKs which are anchored to the plasma membrane. They contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). However, Brk lacks the N-terminal myristoylation sites. Src proteins are involved in signaling pathways that regulate cytokine and growth factor responses, cytoskeleton dynamics, cell proliferation, survival, and differentiation. They were identified as the first proto-oncogene products, and they regulate cell adhesion, invasion, and motility in cancer cells, and tumor vasculature, contributing to cancer progression and metastasis. Src kinases are overexpressed in a variety of human cancers, making them attractive targets for therapy. They are also implicated in acute inflammatory responses and osteoclast function. Src, Fyn, Yes, and Yrk are widely expressed, while Blk, Lck, Hck, Fgr, Lyn, and Brk show a limited expression pattern. This subfamily also includes Drosophila Src42A, Src oncogene at 42A (also known as Dsrc41) which accumulates at sites of cell-cell or cell-matrix adhesion, and participates in Drosphila development and wound healing. It has been shown to promote tube elongation in the tracheal system, is essential for proper cell-cell matching during dorsal closure, and regulates cell-cell contacts in developing Drosophila eyes. The SH3 domain of Src kinases contributes to substrate recruitment by binding adaptor proteins/substrates, and regulation of kinase activity through an intramolecular interaction. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*...
gi 340007427  23 VRAMFDYDKSKDSGLpsqglSFKYGDILHVINASDDEWWQARRVtldgDSEEMGVIPS 80
Cdd:cd11845    2 YVALYDYEARTDDDL-----SFKKGDRLQILDDSDGDWWLARHL----STGKEGYIPS 50

Src homology 3 domain of High osmolarity signaling protein Sho1p; Sho1p (or Sho1), also called SSU81 (Suppressor of SUA8-1 mutation), is a yeast membrane protein that regulates adaptation to high salt conditions by activating the HOG (high-osmolarity glycerol) pathway. High salt concentrations lead to the localization to the membrane of the MAPKK Pbs2, which is then activated by the MAPKK Ste11 and in turn, activates the MAPK Hog1. Pbs2 is localized to the membrane though the interaction of its PxxP motif with the SH3 domain of Sho1p. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*...
gi 340007427  23 VRAMFDYDKSKDSglPSQgLSFKYGDILHVINASdDEWWQARRvtldgDSEEMGVIPS 80
Cdd:cd11855    2 ARALYPYDASPDD--PNE-LSFEKGEILEVSDTS-GKWWQARK-----SNGETGICPS 50

Src Homology 3 domain of metazoan osteoclast stimulating factor 1; OSTF1, also named OSF or SH3P2, is a signaling protein containing SH3 and ankyrin-repeat domains. It acts through a Src-related pathway to enhance the formation of osteoclasts and bone resorption. It also acts as a negative regulator of cell motility. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*...
gi 340007427  23 VRAMFDYDKSKDsglpsQGLSFKYGDILHVINASDDEWWQArrvTLDGDSeemGVIPS 80
Cdd:cd11772    2 FRALYDYEAQHP-----DELSFEEGDLLYISDKSDPNWWKA---TCGGKT---GLIPS 48

C-terminal Src homology 3 domain of Growth factor receptor-bound protein 2; GRB2 is a critical signaling molecule that regulates the Ras pathway by linking tyrosine kinases to the Ras guanine nucleotide releasing protein Sos (son of sevenless), which converts Ras to the active GTP-bound state. It is ubiquitously expressed in all tissues throughout development and is important in cell cycle progression, motility, morphogenesis, and angiogenesis. In lymphocytes, GRB2 is associated with antigen receptor signaling components. GRB2 contains an N-terminal SH3 domain, a central SH2 domain, and a C-terminal SH3 domain. The C-terminal SH3 domain of GRB2 binds to Gab2 (Grb2-associated binder 2) through epitopes containing RxxK motifs, as well as to the proline-rich C-terminus of FGRF2. SH3 domains are protein interaction domains that typically bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  22 YVRAMFDYDKSKDSGLpsqglSFKYGDILHVINASDDEWWQ 62
Cdd:cd11949    1 YVQALFDFDPQEDGEL-----GFRRGDFIEVMDNSDPNWWK 36

First Src Homology 3 domain of the fungal endocytic adaptor protein Sla1p; Sla1p facilitates endocytosis by playing a role as an adaptor protein in coupling components of the actin cytoskeleton to the endocytic machinery. It interacts with Abp1p, Las17p and Pan1p, which are activator proteins of actin-related protein 2/3 (Arp2/3). Sla1p contains multiple domains including three SH3 domains, a SAM (sterile alpha motif) domain, and a Sla1 homology domain 1 (SHD1), which binds to the NPFXD motif that is found in many integral membrane proteins such as the Golgi-localized Arf-binding protein Lsb5p and the P4-ATPases, Drs2p and Dnf1p. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  23 VRAMFDYDKSKDsglpsQGLSFKYGDILHVINASDDEWWQARRVTLDGDS-EEMGVIPS 80
Cdd:cd11773    2 YKALYDYEPQTE-----DELTIQEDDILYLLEKSDDDWWKVKLKVNSSDDdEPVGLVPA 55

C-terminal Src homology 3 domain of GRB2-related adaptor protein; GRAP is a GRB-2 like adaptor protein that is highly expressed in lymphoid tissues. It acts as a negative regulator of T cell receptor (TCR)-induced lymphocyte proliferation by downregulating the signaling to the Ras/ERK pathway. It has been identified as a regulator of TGFbeta signaling in diabetic kidney tubules and may have a role in the pathogenesis of the disease. GRAP contains an N-terminal SH3 domain, a central SH2 domain, and a C-terminal SH3 domain. The C-terminal SH3 domains (SH3c) of the related proteins, GRB2 and GRAP2, have been shown to bind to classical PxxP motif ligands, as well as to non-classical motifs. GRB2 SH3c binds Gab2 (Grb2-associated binder 2) through epitopes containing RxxK motifs, while the SH3c of GRAP2 binds to the phosphatase-like protein HD-PTP via a RxxxxK motif. SH3 domains are protein interaction domains that typically bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  22 YVRAMFDYDKSKDSGLPsqglsFKYGDILHVINASDDEWWQAR 64
Cdd:cd11951    1 FVQAQYDFSAEDPSQLS-----FRRGDIIEVLDCPDPNWWRGR 38

Src homology 3 domain of Fyn and Yrk Protein Tyrosine Kinases; Fyn and Yrk (Yes-related kinase) are members of the Src subfamily of proteins, which are cytoplasmic (or non-receptor) PTKs. Fyn, together with Lck, plays a critical role in T-cell signal transduction by phosphorylating ITAM (immunoreceptor tyr activation motif) sequences on T-cell receptors, ultimately leading to the proliferation and differentiation of T-cells. In addition, Fyn is involved in the myelination of neurons, and is implicated in Alzheimer's and Parkinson's diseases. Yrk has been detected only in chickens. It is primarily found in neuronal and epithelial cells and in macrophages. It may play a role in inflammation and in response to injury. Src kinases contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). The SH3 domain of Src kinases contributes to substrate recruitment by binding adaptor proteins/substrates, and regulation of kinase activity through an intramolecular interaction. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  20 SLYVrAMFDYD-KSKDSglpsqgLSFKYGDILHVINASDDEWWQARRVTLDGDseemGVIPS 80
Cdd:cd12006    1 TLFV-ALYDYEaRTEDD------LSFHKGEKFQILNSSEGDWWEARSLTTGET----GYIPS 51

Src homology 3 domain of Signal Transducing Adaptor Molecule 1; STAM1 is part of the endosomal sorting complex required for transport (ESCRT-0) and is involved in sorting ubiquitinated cargo proteins from the endosome. It may also be involved in the regulation of IL2 and GM-CSF mediated signaling, and has been implicated in neural cell survival. STAMs were discovered as proteins that are highly phosphorylated following cytokine and growth factor stimulation. They function in cytokine signaling and surface receptor degradation, as well as regulate Golgi morphology. They associate with many proteins including Jak2 and Jak3 tyrosine kinases, Hrs, AMSH, and UBPY. STAM adaptor proteins contain VHS (Vps27, Hrs, STAM homology), ubiquitin interacting (UIM), and SH3 domains. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  23 VRAMFDYDKSKDSGLpsqglSFKYGDILHVINASDDEWWQARrvTLDGdseeMGVIPS 80
Cdd:cd11964    3 VRAIYDFEAAEDNEL-----TFKAGDIITILDDSDPNWWKGE--TPQG----TGLFPS 49

Src homology 3 domain of Signal Transducing Adaptor Molecules; STAMs were discovered as proteins that are highly phosphorylated following cytokine and growth factor stimulation. They function in cytokine signaling and surface receptor degradation, as well as regulate Golgi morphology. They associate with many proteins including Jak2 and Jak3 tyrosine kinases, Hrs, AMSH, and UBPY. STAM adaptor proteins contain VHS (Vps27, Hrs, STAM homology), ubiquitin interacting (UIM), and SH3 domains. There are two vertebrate STAMs, STAM1 and STAM2, which may be functionally redundant; vertebrate STAMs contain ITAM motifs. They are part of the endosomal sorting complex required for transport (ESCRT-0). STAM2 deficiency in mice did not cause any obvious abnormality, while STAM1 deficiency resulted in growth retardation. Loss of both STAM1 and STAM2 in mice proved lethal, indicating that STAMs are important for embryonic development. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  23 VRAMFDYDKSKDSGLpsqglSFKYGDILHVINASDDEWWQ 62
Cdd:cd11820    3 VRALYDFEAAEDNEL-----TFKAGEIITVLDDSDPNWWK 37

Src homology 3 domain of Signal Transducing Adaptor Molecule 2; STAM2, also called EAST (Epidermal growth factor receptor-associated protein with SH3 and TAM domain) or Hbp (Hrs binding protein), is part of the endosomal sorting complex required for transport (ESCRT-0). It plays a role in sorting mono-ubiquinated endosomal cargo for trafficking to the lysosome for degradation. It is also involved in the regulation of exocytosis. STAMs were discovered as proteins that are highly phosphorylated following cytokine and growth factor stimulation. They function in cytokine signaling and surface receptor degradation, as well as regulate Golgi morphology. They associate with many proteins including Jak2 and Jak3 tyrosine kinases, Hrs, AMSH, and UBPY. STAM adaptor proteins contain VHS (Vps27, Hrs, STAM homology), ubiquitin interacting (UIM), and SH3 domains. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  23 VRAMFDYDKSKDSGLpsqglSFKYGDILHVINASDDEWWQARrvtldgDSEEMGVIPS 80
Cdd:cd11963    4 VRALYDFEAVEDNEL-----TFKHGEIIIVLDDSDANWWKGE------NHRGVGLFPS 50

Src homology 3 domain of Slit-Robo GTPase Activating Protein 4; srGAP4, also called ARHGAP4, is highly expressed in hematopoietic cells and may play a role in lymphocyte differentiation. It is able to stimulate the GTPase activity of Rac1, Cdc42, and RhoA. In the nervous system, srGAP4 has been detected in differentiating neurites and may be involved in axon and dendritic growth. srGAPs are Rho GAPs that interact with Robo1, the transmembrane receptor of Slit proteins. Slit proteins are secreted proteins that control axon guidance and the migration of neurons and leukocytes. srGAPs contain an N-terminal F-BAR domain, a Rho GAP domain, and a C-terminal SH3 domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  25 AMFDYdkskdSGLPSQGLSFKYGDILHVINASDDEWWQarrvtldGDSEEM-GVIPSK 81
Cdd:cd11956    6 ACFDY-----TGRTAQELSFKRGDVLLLHSKASSDWWR-------GEHNGMrGLIPHK 51

Src Homology 3 domain of Rho GTPase-activating protein 9 and similar proteins; This subfamily is composed of Rho GTPase-activating proteins including mammalian ARHGAP9, and vertebrate ARHGAPs 12 and 27. RhoGAPs (or ARHGAPs) bind to Rho proteins and enhance the hydrolysis rates of bound GTP. ARHGAP9 functions as a GAP for Rac and Cdc42, but not for RhoA. It negatively regulates cell migration and adhesion. It also acts as a docking protein for the MAP kinases Erk2 and p38alpha, and may facilitate cross-talk between the Rho GTPase and MAPK pathways to control actin remodeling. ARHGAP27, also called CAMGAP1, shows GAP activity towards Rac1 and Cdc42. It binds the adaptor protein CIN85 and may play a role in clathrin-mediated endocytosis. ARHGAP12 has been shown to display GAP activity towards Rac1. It plays a role in regulating HFG-driven cell growth and invasiveness. ARHGAPs in this subfamily contain SH3, WW, Pleckstin homology (PH), and RhoGAP domains. SH3 domains bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs; they play a role in the regulation of enzymes by intramolecular interactions, changing the subcellular localization of signal pathway components and mediate multiprotein complex assemblies.

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gi 340007427  22 YVRAMFDYD-KSKDSglpsQGLSFKYGDILHVINASDDEWWQARRvtlDGDSEEMGV 77
Cdd:cd11888    1 YVVVLYPFEyTGKDG----RKVSIKEGERFLLLKKSNDDWWQVRR---PGDSKPFYV 50

Fifth Src homology 3 domain (or SH3E) of Intersectin; Intersectins (ITSNs) are adaptor proteins that function in exo- and endocytosis, actin cytoskeletal reorganization, and signal transduction. They are essential for initiating clathrin-coated pit formation. They bind to many proteins through their multidomain structure and facilitate the assembly of multimeric complexes. Vertebrates contain two ITSN proteins, ITSN1 and ITSN2, which exist in alternatively spliced short and long isoforms. The short isoforms contain two Eps15 homology domains (EH1 and EH2), a coiled-coil region and five SH3 domains (SH3A-E), while the long isoforms, in addition, contain RhoGEF (also called Dbl-homologous or DH), Pleckstrin homology (PH) and C2 domains. ITSN1 and ITSN2 are both widely expressed, with variations depending on tissue type and stage of development. The fifth SH3 domain (or SH3E) of ITSN1 has been shown to bind many protein partners including SGIP1, Sos1, dynamin1/2, CIN85, c-Cbl, SHIP2, N-WASP, and synaptojanin-1, among others. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  23 VRAMFDYDKSKDSGLpsqglSFKYGDILHVINASDDEWWQARrvtLDGDSeemGVIPS 80
Cdd:cd11840    2 VIALFPYTAQNEDEL-----SFQKGDIINVLSKDDPDWWRGE---LNGQT---GLFPS 48

Src homology 3 domain of APC-Stimulated guanine nucleotide Exchange Factor 2; ASEF2, also called Spermatogenesis-associated protein 13 (SPATA13), is a GEF that localizes with actin at the leading edge of cells and is important in cell migration and adhesion dynamics. GEFs activate small GTPases by exchanging bound GDP for free GTP. ASEF2 can activate both Rac 1 and Cdc42, but only Rac1 activation is necessary for increased cell migration and adhesion turnover. Together with APC (adenomatous polyposis coli) and Neurabin2, a scaffold protein that binds F-actin, it is involved in regulating HGF-induced cell migration. ASEF2 contains a SH3 domain followed by RhoGEF (also called Dbl-homologous or DH) and Pleckstrin Homology (PH) domains. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  21 LYVRAMFDYDKSKDsglpsQGLSFKYGDILHVINASDDEWWQAR 64
Cdd:cd11974    1 VYAEALWDHVTMDD-----QELAFKAGDVIRVLEASNKDWWWGR 39

Second Src Homology 3 domain of FCH and double SH3 domains proteins; This group is composed of FCH and double SH3 domains protein 1 (FCHSD1) and FCHSD2. These proteins have a common domain structure consisting of an N-terminal F-BAR (FES-CIP4 Homology and Bin/Amphiphysin/Rvs), two SH3, and C-terminal proline-rich domains. They have only been characterized in silico and their functions remain unknown. This group also includes the insect protein, nervous wreck, which acts as a regulator of synaptic growth signaling. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  22 YVRAMFDYDKSKDsglpsQGLSFKYGDILHVINAS----DDEWWQARrvtLDGdseEMGVIPS 80
Cdd:cd11762    1 LVRALYDYEAQSD-----EELSFPEGAIIRILRKDdngvDDGWWEGE---FNG---RVGVFPS 52

Src Homology 3 domain of Voltage-dependent L-type calcium channel subunit beta4; The beta4 subunit of voltage-dependent calcium channels (Ca(V)s) is one of four beta subunits present in vertebrates. It is the only beta subunit expressed in the cochlea and is highly expressed in the brain, predominantly in the cerebellum. Ca(V)s are multi-protein complexes that regulate the entry of calcium into cells. They impact muscle contraction, neuronal migration, hormone and neurotransmitter release, and the activation of calcium-dependent signaling pathways. They are composed of four subunits: alpha1, alpha2delta, beta, and gamma. The beta subunit is a soluble and intracellular protein that interacts with the transmembrane alpha1 subunit. It facilitates the trafficking and proper localization of the alpha1 subunit to the cellular plasma membrane. Vertebrates contain four different beta subunits from distinct genes (beta1-4); each exists as multiple splice variants. All are expressed in the brain while other tissues show more specific expression patterns. The beta subunits show similarity to MAGUK (membrane-associated guanylate kinase) proteins in that they contain SH3 and inactive guanylate kinase (GuK) domains; however, they do not appear to contain a PDZ domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 340007427  33 KDSGLPSQGLSFKYGDILHVINASDDEWWQARRVTldgDSEEMGVIPSKRRVE 85
Cdd:cd12043   19 EDVPVPGTAISFDAKDFLHIKEKYNNDWWIGRLVK---EGCEIGFIPSPLRLE 68