Fifth domain (immunoglobulin-like) of Trk receptors TrkA, TrkB, and TrkC; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fifth domain of Trk receptors TrkA, TrkB, and TrkC, an immunoglobulin (Ig)-like domain which binds to neurotrophin. The Trk family of receptors are tyrosine kinase receptors. They are activated by dimerization, leading to autophosphorylation of intracellular tyrosine residues, and triggering the signal transduction pathway. TrkA, TrkB, and TrkC share significant sequence homology and domain organization. The first three domains are leucine-rich domains while the fourth and fifth domains are Ig-like domains playing a part in ligand binding. TrkA, TrkB, and TrkC mediate the trophic effects of the neurotrophin Nerve Growth Factor (NGF) family. TrkA is recognized by NGF. TrkB is recognized by brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-4. TrkC is recognized by NT-3. NT-3 is promiscuous as in some cell systems it activates TrkA and TrkB receptors. TrkA is a receptor found in all major NGF targets, including the sympathetic, trigeminal, and dorsal root ganglia, cholinergic neurons of the basal forebrain, and the striatum. TrKB transcripts are found throughout multiple structures of the central and peripheral nervous systems. The TrkC gene is expressed throughout the mammalian nervous system. This group belongs to the I-set of IgSF domains.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025 304 PPRVVSLEEPELRLEHCIEFVVRGNPPPTLHWLHNGQPLRESKIIHVEYYQEG---EISEGCLLFNKPTHYNNGNYTLIA 380
Cdd:cd04971    1 APVIVRLEEPELRHHWCIPFTVRGNPKPTLTWYHNGAVLNESDYIRTEIHYEAatpTEYHGCLKFDNPTHVNNGNYTLVA 80

                         90
                 ....*....|....*.
gi 578827025 381 KNPLGTANQTINGHFL 396
Cdd:cd04971   81 SNEYGQDSKSISAHFM 96

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

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025  214 VSHVNLTVREGDNAVITCNGS-GSPLPDVDWIVTGLQSINTHQTNLNWTNVHAINLTLVNVTSEDNGfTLTCIAENVVGM 292
Cdd:pfam00047   1 SAPPTVTVLEGDSATLTCSAStGSPGPDVTWSKEGGTLIESLKVKHDNGRTTQSSLLISNVTKEDAG-TYTCVVNNPGGS 79

                  ....*..
gi 578827025  293 SNASVAL 299
Cdd:pfam00047  80 ATLSTSL 86

Leucine rich repeat N-terminal domain; Leucine Rich Repeats pfam00560 are short sequence motifs present in a number of proteins with diverse functions and cellular locations. Leucine Rich Repeats are often flanked by cysteine rich domains. This domain is often found at the N-terminus of tandem leucine rich repeats.

                          10        20
                  ....*....|....*....|.
gi 578827025   31 ACPANCVCSKTEINCRRPDDG 51
Cdd:pfam01462   1 ACPVPCHCSATVVNCSDRGLT 21

Fifth domain (immunoglobulin-like) of Trk receptors TrkA, TrkB, and TrkC; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fifth domain of Trk receptors TrkA, TrkB, and TrkC, an immunoglobulin (Ig)-like domain which binds to neurotrophin. The Trk family of receptors are tyrosine kinase receptors. They are activated by dimerization, leading to autophosphorylation of intracellular tyrosine residues, and triggering the signal transduction pathway. TrkA, TrkB, and TrkC share significant sequence homology and domain organization. The first three domains are leucine-rich domains while the fourth and fifth domains are Ig-like domains playing a part in ligand binding. TrkA, TrkB, and TrkC mediate the trophic effects of the neurotrophin Nerve Growth Factor (NGF) family. TrkA is recognized by NGF. TrkB is recognized by brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-4. TrkC is recognized by NT-3. NT-3 is promiscuous as in some cell systems it activates TrkA and TrkB receptors. TrkA is a receptor found in all major NGF targets, including the sympathetic, trigeminal, and dorsal root ganglia, cholinergic neurons of the basal forebrain, and the striatum. TrKB transcripts are found throughout multiple structures of the central and peripheral nervous systems. The TrkC gene is expressed throughout the mammalian nervous system. This group belongs to the I-set of IgSF domains.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025 304 PPRVVSLEEPELRLEHCIEFVVRGNPPPTLHWLHNGQPLRESKIIHVEYYQEG---EISEGCLLFNKPTHYNNGNYTLIA 380
Cdd:cd04971    1 APVIVRLEEPELRHHWCIPFTVRGNPKPTLTWYHNGAVLNESDYIRTEIHYEAatpTEYHGCLKFDNPTHVNNGNYTLVA 80

                         90
                 ....*....|....*.
gi 578827025 381 KNPLGTANQTINGHFL 396
Cdd:cd04971   81 SNEYGQDSKSISAHFM 96

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

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025  214 VSHVNLTVREGDNAVITCNGS-GSPLPDVDWIVTGLQSINTHQTNLNWTNVHAINLTLVNVTSEDNGfTLTCIAENVVGM 292
Cdd:pfam00047   1 SAPPTVTVLEGDSATLTCSAStGSPGPDVTWSKEGGTLIESLKVKHDNGRTTQSSLLISNVTKEDAG-TYTCVVNNPGGS 79

                  ....*..
gi 578827025  293 SNASVAL 299
Cdd:pfam00047  80 ATLSTSL 86

Leucine rich repeat;

                          10        20        30        40        50
                  ....*....|....*....|....*....|....*....|....*....|....*....
gi 578827025  103 TGLQKLTIKNSGLRSIQPRAFAKNPHLRYINLSSNRLTTLSWQLFQTL-SLRELQLEQN 160
Cdd:pfam13855   1 PNLRSLDLSNNRLTSLDDGAFKGLSNLKVLDLSNNLLTTLSPGAFSGLpSLRYLDLSGN 59

Leucine rich repeat C-terminal domain;

                           10        20        30        40
                   ....*....|....*....|....*....|....*....|....*.
gi 578827025   160 NFFNCSCDIRWMQLWQEQGEAKLNSQNLYCINADGSQLPLFRMNIS 205
Cdd:smart00082   1 NPFICDCELRWLLRWLQANEHLQDPVDLRCASPSSLRGPLLELLHS 46

Leucine-rich repeat (LRR) protein [Transcription];

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025  75 DISRN-ITSI--HIENWRSLHTLNAVDMEL---------YTGLQKLTIKNSGLRSIqPRAFAKNPHLRYINLSSNRLTTL 142
Cdd:COG4886  119 DLSGNqLTDLpeELANLTNLKELDLSNNQLtdlpeplgnLTNLKSLDLSNNQLTDL-PEELGNLTNLKELDLSNNQITDL 197

                         90
                 ....*....|....*...
gi 578827025 143 SWQLFQTLSLRELQLEQN 160
Cdd:COG4886  198 PEPLGNLTNLEELDLSGN 215

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

                           10        20        30        40        50        60
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 578827025   325 VRGNPPPTLHWLHNG-QPLRESKIIHVEYYQegeiSEGCLLFNKPTHYNNGNYTLIAKNPLGTANQTIN 392
Cdd:smart00410  18 ASGSPPPEVTWYKQGgKLLAESGRFSVSRSG----STSTLTISNVTPEDSGTYTCAATNSSGSASSGTT 82

Fifth domain (immunoglobulin-like) of Trk receptors TrkA, TrkB, and TrkC; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fifth domain of Trk receptors TrkA, TrkB, and TrkC, an immunoglobulin (Ig)-like domain which binds to neurotrophin. The Trk family of receptors are tyrosine kinase receptors. They are activated by dimerization, leading to autophosphorylation of intracellular tyrosine residues, and triggering the signal transduction pathway. TrkA, TrkB, and TrkC share significant sequence homology and domain organization. The first three domains are leucine-rich domains while the fourth and fifth domains are Ig-like domains playing a part in ligand binding. TrkA, TrkB, and TrkC mediate the trophic effects of the neurotrophin Nerve Growth Factor (NGF) family. TrkA is recognized by NGF. TrkB is recognized by brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-4. TrkC is recognized by NT-3. NT-3 is promiscuous as in some cell systems it activates TrkA and TrkB receptors. TrkA is a receptor found in all major NGF targets, including the sympathetic, trigeminal, and dorsal root ganglia, cholinergic neurons of the basal forebrain, and the striatum. TrKB transcripts are found throughout multiple structures of the central and peripheral nervous systems. The TrkC gene is expressed throughout the mammalian nervous system. This group belongs to the I-set of IgSF domains.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025 304 PPRVVSLEEPELRLEHCIEFVVRGNPPPTLHWLHNGQPLRESKIIHVEYYQEG---EISEGCLLFNKPTHYNNGNYTLIA 380
Cdd:cd04971    1 APVIVRLEEPELRHHWCIPFTVRGNPKPTLTWYHNGAVLNESDYIRTEIHYEAatpTEYHGCLKFDNPTHVNNGNYTLVA 80

                         90
                 ....*....|....*.
gi 578827025 381 KNPLGTANQTINGHFL 396
Cdd:cd04971   81 SNEYGQDSKSISAHFM 96

Leucine rich repeat C-terminal motif; This entry represents the Leucine Rich Repeat C-terminal (LRRCT) capping motif from TRK receptors.

                          10        20        30        40
                  ....*....|....*....|....*....|....*....|....*.
gi 578827025  163 NCSCDIRWMQLWQEQGEAKLNSQNLYCINaDGSQLPLFRMNISQCD 208
Cdd:pfam16920   1 RCSCDIRWLQLWQEEGLAGLGTQQLYCLN-DGSKIPLQSMNIPNCG 45

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025   218 NLTVREGDNAVITCNGSGSPLPDVDWIVTGLQSInTHQTNLNWTNVHAI-NLTLVNVTSEDNGfTLTCIAENVVGMSNAS 296
Cdd:smart00410   3 SVTVKEGESVTLSCEASGSPPPEVTWYKQGGKLL-AESGRFSVSRSGSTsTLTISNVTPEDSG-TYTCAATNSSGSASSG 80

                   ....*
gi 578827025   297 VALTV 301
Cdd:smart00410  81 TTLTV 85

Leucine rich repeat;

                          10        20        30        40        50
                  ....*....|....*....|....*....|....*....|....*....|....*....
gi 578827025  103 TGLQKLTIKNSGLRSIQPRAFAKNPHLRYINLSSNRLTTLSWQLFQTL-SLRELQLEQN 160
Cdd:pfam13855   1 PNLRSLDLSNNRLTSLDDGAFKGLSNLKVLDLSNNLLTTLSPGAFSGLpSLRYLDLSGN 59

Leucine rich repeat C-terminal domain;

                           10        20        30        40
                   ....*....|....*....|....*....|....*....|....*.
gi 578827025   160 NFFNCSCDIRWMQLWQEQGEAKLNSQNLYCINADGSQLPLFRMNIS 205
Cdd:smart00082   1 NPFICDCELRWLLRWLQANEHLQDPVDLRCASPSSLRGPLLELLHS 46

Fourth domain (immunoglobulin-like) of Trk receptors TrkA, TrkB, and TrkC; The members here are composed of the fourth domain of Trk receptors TrkA, TrkB, and TrkC, an immunoglobulin (Ig)-like domain which binds to neurotrophin. The Trk family of receptors are tyrosine kinase receptors. They are activated by dimerization, leading to autophosphorylation of intracellular tyrosine residues, and triggering the signal transduction pathway. TrkA, TrkB, and TrkC share significant sequence homology and domain organization. The first three domains are leucine-rich domains while the fourth and fifth domains are Ig-like domains playing a part in ligand binding. TrkA, TrkB, and TrkC mediate the trophic effects of the neurotrophin Nerve Growth Factor (NGF) family. TrkA is recognized by NGF. TrKB is recognized by brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-4. TrkC is recognized by NT-3. NT-3 is promiscuous as in some cell systems it activates TrkA and TrkB receptors. TrkA is a receptor found in all major NGF targets, including the sympathetic, trigeminal, and dorsal root ganglia, cholinergic neurons of the basal forebrain, and the striatum. TrKB transcripts are found throughout multiple structures of the central and peripheral nervous systems. The TrkC gene is expressed throughout the mammalian nervous system.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025 211 EISVSHVNLTVREGDNAVITCNGSGSPLPDVDWIVTGLQSintHQTNLNWTNVHAINLTLVNVTSEDNGFTLTCIAENVV 290
Cdd:cd04972    1 TLKIQMPNASVDVGDDVLLQCQVEGQGLEQAGWILTELEQ---SATVMKSGSLPSLGLTLANVTSDLNRKNVTCWAENDV 77

                         90
                 ....*....|.
gi 578827025 291 GMSNASVALTV 301
Cdd:cd04972   78 GRAEVSVQVNV 88

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        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025 217 VNLTVREGDNAVITCNGSGSPLPDVDWIVTG--LQSINTHQTNLNwtnvhaiNLTLVNVTSEDNGfTLTCIAENVVGMSN 294
Cdd:cd05725    5 QNQVVLVDDSAEFQCEVGGDPVPTVRWRKEDgeLPKGRYEILDDH-------SLKIRKVTAGDMG-SYTCVAENMVGKIE 76

                 ....*..
gi 578827025 295 ASVALTV 301
Cdd:cd05725   77 ASATLTV 83

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

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|..
gi 578827025 227 AVITCNGSGSPLPDVDWIVTGLQSINTHQTNLNWTNVHAiNLTLVNVTSEDNGfTLTCIAENVVGMSNASVA 298
Cdd:cd00096    1 VTLTCSASGNPPPTITWYKNGKPLPPSSRDSRRSELGNG-TLTISNVTLEDSG-TYTCVASNSAGGSASASV 70

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 578827025 218 NLTVREGDNAVITCNGSGSPLPDVDWIVTG--LQSINT-HQTNLNWTnvhaiNLTLVNVTSEDNGFTLtCIAENVVG 291
Cdd:cd20970   11 TVTAREGENATFMCRAEGSPEPEISWTRNGnlIIEFNTrYIVRENGT-----TLTIRNIRRSDMGIYL-CIASNGVP 81

immunoglobulin-like domain of telokin and similar proteins; a member of the I-set of IgSF domains; The members here are composed of the immunoglobulin (Ig) domain in telokin, the C-terminal domain of myosin light chain kinase which is identical to telokin, and similar proteins. 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 telokin Ig domain 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
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 578827025 325 VRGNPPPTLHWLHNGQPLRESKIIHVEYYQEGEISegcLLFNKPTHYNNGNYTLIAKNPLGTANQT 390
Cdd:cd20973   21 VEGYPDPEVKWMKDDNPIVESRRFQIDQDEDGLCS---LIISDVCGDDSGKYTCKAVNSLGEATCS 83

Second immunoglobulin (Ig)-like domain of fibroblast growth factor (FGF) receptor; member of the I-set of IgSF domains; The members here are composed of the second immunoglobulin (Ig)-like domain of fibroblast growth factor (FGF) receptor. FGF receptors bind FGF signaling polypeptides. FGFs participate in multiple processes such as morphogenesis, development, and angiogenesis. FGFs bind to four FGF receptor tyrosine kinases (FGFR1, FGFR2, FGFR3, FGFR4). Receptor diversity is controlled by alternative splicing producing splice variants with different ligand binding characteristics and different expression patterns. FGFRs have an extracellular region comprised of three IG-like domains, a single transmembrane helix, and an intracellular tyrosine kinase domain. Ligand binding and specificity reside in the Ig-like domains 2 and 3, and the linker region that connects these two. FGFR activation and signaling depend on FGF-induced dimerization, a process involving cell surface heparin or heparin sulfate proteoglycans.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 578827025 325 VRGNPPPTLHWLHNGQPLR-ESKI--IHVEYYQEGEISEGCLLFNKpthynnGNYTLIAKNPLGTANQT 390
Cdd:cd05857   28 AAGNPTPTMRWLKNGKEFKqEHRIggYKVRNQHWSLIMESVVPSDK------GNYTCVVENEYGSINHT 90

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

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 578827025 324 VVRGNPPPTLHWLHNGQPLRESKIIHVEYYQegeiSEGCLLFNKPTHYNNGNYTLIAKNPLGTANQTI 391
Cdd:cd00096    6 SASGNPPPTITWYKNGKPLPPSSRDSRRSEL----GNGTLTISNVTLEDSGTYTCVASNSAGGSASAS 69

Immunoglobulin (Ig)-like domain in neuregulins; The members here are composed of the immunoglobulin (Ig)-like domain in neuregulins (NRGs). NRGs are signaling molecules which participate in cell-cell interactions in the nervous system, breast, heart, and other organ systems, and are implicated in the pathology of diseases including schizophrenia, multiple sclerosis, and breast cancer. There are four members of the neuregulin gene family (NRG-1, NRG-2, NRG-3, and NRG-4). The NRG-1 protein, binds to and activates the tyrosine kinases receptors ErbB3 and ErbB4, initiating signaling cascades. The other NRGs proteins bind one or the other or both of these ErbBs. NRG-1 has multiple functions: in the brain it regulates various processes such as radial glia formation and neuronal migration, dendritic development, and expression of neurotransmitters receptors, while in the peripheral nervous system NRG-1 regulates processes such as target cell differentiation, and Schwann cell survival. There are many NRG-1 isoforms which arise from the alternative splicing of mRNA. Less is known of the functions of the other NRGs. NRG-2 and NRG-3 are expressed predominantly in the nervous system. NRG-2 is expressed by motor neurons and terminal Schwann cells, and is concentrated near synaptic sites and may be a signal that regulates synaptic differentiation. NRG-4 has been shown to direct pancreatic islet cell development towards the delta-cell lineage.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 578827025 327 GNPPPTLHWLHNGQPLRESKIIHVEYYQEGEISEgcLLFNKPTHYNNGNYTLIAKNPLGTANQTINGH 394
Cdd:cd05750   26 ENPSPRYRWFKDGKELNRKRPKNIKIRNKKKNSE--LQINKAKLEDSGEYTCVVENILGKDTVTGNVT 91

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

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....
gi 578827025 319 HCIEFVVRGNPPPTLHWLHNGQPLRESKIIHVEyyqEGEISEgCLLFNKPTHYNNGNYTLIAKNPLGTANQTIN 392
Cdd:cd05748   10 LRLDIPIKGRPTPTVTWSKDGQPLKETGRVQIE---TTASST-SLVIKNAKRSDSGKYTLTLKNSAGEKSATIN 79

C-terminal immunoglobulin-like domain of the myosin-associated giant protein kinase Twitchin, and similar domains; member of the I-set IgSF domains; The members here are composed of the C-terminal immunoglobulin-like domain of the myosin-associated giant protein kinase Twitchin and similar proteins, including Caenorhabditis elegans and Aplysia californica Twitchin, Drosophila melanogaster Projectin, and similar proteins. These are very large muscle proteins containing multiple immunoglobulin (Ig)-like and fibronectin type III (FN3) domains and a single kinase domain near the C-terminus. In humans these proteins are called Titin. 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. The Ig-like domain of the Twitchin is a member of the I-set 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. 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.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025 219 LTVREGDNAVITCNGSGSPLPDVDWIVTGlQSINTHQTNLNWTNVHAINLTLVNVTSEDNGfTLTCIAENVVGMSNASVA 298
Cdd:cd20949    9 TTVKEGQSATILCEVKGEPQPNVTWHFNG-QPISASVADMSKYRILADGLLINKVTQDDTG-EYTCRAYQVNSIASDMQE 86

                 ...
gi 578827025 299 LTV 301
Cdd:cd20949   87 RTV 89

Leucine-rich repeat (LRR) protein [Transcription];

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025  75 DISRN-ITSI--HIENWRSLHTLNAVDMEL---------YTGLQKLTIKNSGLRSIqPRAFAKNPHLRYINLSSNRLTTL 142
Cdd:COG4886  119 DLSGNqLTDLpeELANLTNLKELDLSNNQLtdlpeplgnLTNLKSLDLSNNQLTDL-PEELGNLTNLKELDLSNNQITDL 197

                         90
                 ....*....|....*...
gi 578827025 143 SWQLFQTLSLRELQLEQN 160
Cdd:COG4886  198 PEPLGNLTNLEELDLSGN 215

Fourth immunoglobulin (Ig)-like domain in neogenin, and similar domains; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fourth immunoglobulin (Ig)-like domain in neogenin and related proteins. Neogenin is a cell surface protein which is expressed in the developing nervous system of vertebrate embryos in the growing nerve cells. It is also expressed in other embryonic tissues, and may play a general role in developmental processes such as cell migration, cell-cell recognition, and tissue growth regulation. Included in this group is the tumor suppressor protein DCC which is deleted in colorectal carcinoma. DCC and neogenin each have four Ig-like domains followed by six fibronectin type III domains, a transmembrane domain, and an intracellular domain. 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        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025 217 VNLTVREGDNAVITCNGSGSPLPDVDWIVTGLQSINTHQTNLnwtnVHAINLTLVNVTSEDNGFtLTCIAENVVGMSNAS 296
Cdd:cd05723    5 SNIYAHESMDIVFECEVTGKPTPTVKWVKNGDVVIPSDYFKI----VKEHNLQVLGLVKSDEGF-YQCIAENDVGNAQAS 79

                 ....*
gi 578827025 297 VALTV 301
Cdd:cd05723   80 AQLII 84

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

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025 210 PEISVSHVNLTVREGDNAVITCNGSGSPLPDVDWIVTGLQSINTHQTNLN-WTNVHAINLTLVNVTS---EDNGFtLTCI 285
Cdd:cd20956    2 PVLLETFSEQTLQPGPSVSLKCVASGNPLPQITWTLDGFPIPESPRFRVGdYVTSDGDVVSYVNISSvrvEDGGE-YTCT 80

                 ....*.
gi 578827025 286 AENVVG 291
Cdd:cd20956   81 ATNDVG 86

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

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025 210 PEISVSHVNLTVREGDNAVITCNGSGSPLPDVDWIVTGLqSINTHQTN-----LNWTNVHainltLVNVTSEDNGfTLTC 284
Cdd:cd05736    1 PVIRVYPEFQAKEPGVEASLRCHAEGIPLPRVQWLKNGM-DINPKLSKqltliANGSELH-----ISNVRYEDTG-AYTC 73

                 ....*...
gi 578827025 285 IAENVVGM 292
Cdd:cd05736   74 IAKNEGGV 81

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
                 ....*....|....*....|....*....|....*....|....*....|....*....|.
gi 578827025 326 RGNPPPTLHWLHNGQPLRESKiIHVEyyqegEISEGCLLFNKPTHYNNGNYTLIAKNPLGT 386
Cdd:cd05724   23 RGHPEPTVSWRKDGQPLNLDN-ERVR-----IVDDGNLLIAEARKSDEGTYKCVATNMVGE 77

Sixth immunoglobulin (Ig) domain of contactin-2; The members here are composed of the sixth immunoglobulin (Ig) domain of the neural cell adhesion molecule contactin-2-like. Contactins are comprised of six Ig domains followed by four fibronectin type III (FnIII) domains anchored to the membrane by glycosylphosphatidylinositol. Contactin-2 (TAG-1, axonin-1) facilitates cell adhesion by homophilic binding between molecules in apposed membranes. It may play a part in the neuronal processes of neurite outgrowth, axon guidance and fasciculation, and neuronal migration. 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. The different contactins show different expression patterns in the central nervous system. During development and in adulthood, contactin-2 is transiently expressed in subsets of central and peripheral neurons. Contactin-2 is also expressed in retinal amacrine cells (AC) in the developing chick retina, corresponding to the period of formation and maturation of AC processes.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025 208 DLPEISVSHVNLTVREGDNAVITCNGSGSPLPDVD--WIVTG----LQSINTHQTNLNWTNVHAiNLTLVNVTSEDNGfT 281
Cdd:cd05854    1 DATKITLAPSSADINQGENLTLQCHASHDPTMDLTftWSLDDfpidLDKPNGHYRRMEVKETIG-DLVIVNAQLSHAG-T 78

                         90       100
                 ....*....|....*....|....
gi 578827025 282 LTCIAENVVGMSNASVALTVYYPP 305
Cdd:cd05854   79 YTCTAQTVVDSASASATLVVRGPP 102

Immunoglobulin (Ig)-like domain of myotilin, palladin, and myopalladin; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig)-like domain in myotilin, palladin, and myopalladin. Myotilin, palladin, and myopalladin function as scaffolds that regulate actin organization. Myotilin and myopalladin are most abundant in skeletal and cardiac muscle; palladin is ubiquitously expressed in the organs of developing vertebrates and plays a key role in cellular morphogenesis. The three family members each interact with specific molecular partners with all three binding to alpha-actinin; In addition, palladin also binds to vasodilator-stimulated phosphoprotein (VASP) and ezrin, myotilin binds to filamin and actin, and myopalladin also binds to nebulin and cardiac ankyrin repeat protein (CARP). 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
                 ....*....|....*....|....*....|....*....|....*....|....*....|....
gi 578827025 325 VRGNPPPTLHWLHNGQPLRESKiIHVEYYQE-GEISegcLLFNKPTHYNNGNYTLIAKNPLGTA 387
Cdd:cd05744   24 VSGLPTPDLFWQLNGKPVRPDS-AHKMLVREnGRHS---LIIEPVTKRDAGIYTCIARNRAGEN 83

Immunoglobulin domain; This domain contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025  210 PEISVShvNLTVREGDNAVITCNGSGSPLPDVDWiVTGLQSINTHQtnlnwtnvhaiNLTLVNVTSEDNGfTLTCIAEN- 288
Cdd:pfam13895   2 PVLTPS--PTVVTEGEPVTLTCSAPGNPPPSYTW-YKDGSAISSSP-----------NFFTLSVSAEDSG-TYTCVARNg 66

                          90
                  ....*....|...
gi 578827025  289 VVGMSNASVALTV 301
Cdd:pfam13895  67 RGGKVSNPVELTV 79

Leucine-rich repeat (LRR) protein [Transcription];

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025  75 DISRN-ITSIH--IENWRSLHTLNA-------VDMELY--TGLQKLTIKNSGLRSIqPRAFAKNPHLRYINLSSNRLTTL 142
Cdd:COG4886  142 DLSNNqLTDLPepLGNLTNLKSLDLsnnqltdLPEELGnlTNLKELDLSNNQITDL-PEPLGNLTNLEELDLSGNQLTDL 220

                         90
                 ....*....|....*...
gi 578827025 143 SWQLFQTLSLRELQLEQN 160
Cdd:COG4886  221 PEPLANLTNLETLDLSNN 238

Immunoglobulin domain of human Synaptic Adhesion-Like Molecule 5 (SALM5) and similar proteins; member of the I-set of IgSF domains; This group contains the immunoglobulin domain of human Synaptic Adhesion-Like Molecule 5 (SALM5) and similar proteins. The SALM (for synaptic adhesion-like molecules; also known as Lrfn for leucine-rich repeat and fibronectin type III domain containing) family of adhesion molecules consists of five known members: SALM1/Lrfn2, SALM2/Lrfn1, SALM3/Lrfn4, SALM4/Lrfn3, and SALM5/Lrfn5. SALMs share a similar domain structure, containing leucine-rich repeats (LRRs), an immunoglobulin (Ig) domain, and a fibronectin III (FNIII) domain, followed by a transmembrane domain and a C-terminal PDZ-binding motif. SALM5 is implicated in autism spectrum disorders (ASDs) and schizophrenia, induces presynaptic differentiation in contacting axons. SALM5 interacts with the Ig domains of LAR (Leukocyte common Antigen-Related) family receptor protein tyrosine phosphatases (LAR-RPTPs; LAR, PTPdelta, and PTPsigma). In addition, PTPdelta is implicated in ASDs, ADHD, bipolar disorder, and restless leg syndrome. Studies have shown that LAR-RPTPs are novel and splicing-dependent presynaptic ligands for SALM5, and that they mediate SALM5-dependent presynaptic differentiation. Furthermore, SALM5 maintains AMPA receptor (AMPAR)-mediated excitatory synaptic transmission through mechanisms involving the interaction of SALM5 with LAR-RPTPs. This group belongs to the I-set of immunoglobulin superfamily (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        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 578827025 219 LTVREGDNAVITCNGSGSPLPDVDWIVTGLQSI-NTHQTNLNWTNVHAINLTlvnvTSEDNGfTLTCIAENVVGMSNASV 297
Cdd:cd05764   10 LRVLEGQRATLRCKARGDPEPAIHWISPEGKLIsNSSRTLVYDNGTLDILIT----TVKDTG-AFTCIASNPAGEATARV 84

                 ....
gi 578827025 298 ALTV 301
Cdd:cd05764   85 ELHI 88

Immunoglobulin (Ig)-like I-set domain of Neural Cell Adhesion Molecule 1 (NCAM-1); The members here are composed of the fourth Ig domain of Neural Cell Adhesion Molecule 1(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. 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 578827025 210 PEISVSHVNLTVREGDNAVITCNGSGSPLPDVDWiVTGLQSINTHQTNLNWTNV---HA--INLTLVNVTSEDNGFTLtC 284
Cdd:cd05869    3 PKITYVENQTAMELEEQITLTCEASGDPIPSITW-RTSTRNISSEEKTLDGHIVvrsHArvSSLTLKYIQYTDAGEYL-C 80