Second immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs), and similar domains; The members here are composed of the second immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs). Interactions between IgG and FcgammaR are important to the initiation of cellular and humoral response. IgG binding to FcgammaR leads to a cascade of signals and ultimately to functions such as antibody-dependent-cellular-cytotoxicity (ADCC), endocytosis, phagocytosis, release of inflammatory mediators, etc. FcgammaR has two Ig-like domains. This group also contains FcepsilonRI which binds IgE with high affinity.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741 132 WLVLQTPHLEFQEGETIVLRCHSWKDKPLVKVTFFQNGKSKKFSRSDPNFSIPQANHSHSGDYHCTGNIGYTLYSSKPVT 211
Cdd:cd05753     1 WLLLQAPSAVVFEGEPLTLRCHGWKDKKVHKVTYYKDGKALKFSYENSNFSIPQATLSDSGSYHCSGTVRIKRRSSESVN 80

                  ...
gi 1883684741 212 ITV 214
Cdd:cd05753    81 ITV 83

Second immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs), and similar domains; The members here are composed of the second immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs). Interactions between IgG and FcgammaR are important to the initiation of cellular and humoral response. IgG binding to FcgammaR leads to a cascade of signals and ultimately to functions such as antibody-dependent-cellular-cytotoxicity (ADCC), endocytosis, phagocytosis, release of inflammatory mediators, etc. FcgammaR has two Ig-like domains. This group also contains FcepsilonRI which binds IgE with high affinity.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741 132 WLVLQTPHLEFQEGETIVLRCHSWKDKPLVKVTFFQNGKSKKFSRSDPNFSIPQANHSHSGDYHCTGNIGYTLYSSKPVT 211
Cdd:cd05753     1 WLLLQAPSAVVFEGEPLTLRCHGWKDKKVHKVTYYKDGKALKFSYENSNFSIPQATLSDSGSYHCSGTVRIKRRSSESVN 80

                  ...
gi 1883684741 212 ITV 214
Cdd:cd05753    81 ITV 83

Immunoglobulin domain; This domain contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741 132 WLVLQTPHLEFQEGETIVLRCHSWkDKPLVKVTFFQNGKskkFSRSDPNFSIPQANHSHSGDYHCTGNIGYTLYSSKPVT 211
Cdd:pfam13895   1 KPVLTPSPTVVTEGEPVTLTCSAP-GNPPPSYTWYKDGS---AISSSPNFFTLSVSAEDSGTYTCVARNGRGGKVSNPVE 76

                  ...
gi 1883684741 212 ITV 214
Cdd:pfam13895  77 LTV 79

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741  138 PHLEFQEGETIVLRCHSWkDKPLVKVTFFQNGKSK-------KFSRSDPNFS--IPQANHSHSGDYHCTGNIGYTLYSSk 208
Cdd:smart00410   2 PSVTVKEGESVTLSCEAS-GSPPPEVTWYKQGGKLlaesgrfSVSRSGSTSTltISNVTPEDSGTYTCAATNSSGSASS- 79

                   ....*.
gi 1883684741  209 PVTITV 214
Cdd:smart00410  80 GTTLTV 85

IL-1 receptor-like protein; Provisional

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741  59 INVLQEDSVTLTCRGTHSPESD----------SIQWFHNGNLI-------------PTHTQPSYR------FKANNNDSG 109
Cdd:PHA02826   32 VYAKFGDPMVLLCTGKHYKKSIffdktfitsyNVTWSKTDSLAfvrdsgartkikkITHNEIGDRsenlwiGNVINIDEG 111

                          90       100       110       120       130       140       150       160
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741 110 EYTCQ--TGQTSLSDPVHLTVLSEwlvlqTPHLEFQEGETIVLRCH-------SWKDKPLvkvTFFQNGK----SKKFSR 176
Cdd:PHA02826  112 IYICTisSGNICEESTIRLTFDSG-----TINYQFNSGKDSKLHCYgtdgissTFKDYTL---TWYKNGNivlyTDRIQL 183

                         170       180
                  ....*....|....*....|....*...
gi 1883684741 177 SDPN--FSIPQANHSHSGDYHCTGNIGY 202
Cdd:PHA02826  184 RNNNstLVIKSATHDDSGIYTCNLRFNK 211

Second immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs), and similar domains; The members here are composed of the second immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs). Interactions between IgG and FcgammaR are important to the initiation of cellular and humoral response. IgG binding to FcgammaR leads to a cascade of signals and ultimately to functions such as antibody-dependent-cellular-cytotoxicity (ADCC), endocytosis, phagocytosis, release of inflammatory mediators, etc. FcgammaR has two Ig-like domains. This group also contains FcepsilonRI which binds IgE with high affinity.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741 132 WLVLQTPHLEFQEGETIVLRCHSWKDKPLVKVTFFQNGKSKKFSRSDPNFSIPQANHSHSGDYHCTGNIGYTLYSSKPVT 211
Cdd:cd05753     1 WLLLQAPSAVVFEGEPLTLRCHGWKDKKVHKVTYYKDGKALKFSYENSNFSIPQATLSDSGSYHCSGTVRIKRRSSESVN 80

                  ...
gi 1883684741 212 ITV 214
Cdd:cd05753    81 ITV 83

Immunoglobulin domain; This domain contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741 132 WLVLQTPHLEFQEGETIVLRCHSWkDKPLVKVTFFQNGKskkFSRSDPNFSIPQANHSHSGDYHCTGNIGYTLYSSKPVT 211
Cdd:pfam13895   1 KPVLTPSPTVVTEGEPVTLTCSAP-GNPPPSYTWYKDGS---AISSSPNFFTLSVSAEDSGTYTCVARNGRGGKVSNPVE 76

                  ...
gi 1883684741 212 ITV 214
Cdd:pfam13895  77 LTV 79

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 1883684741  47 PPkaVLKLEPQWINVLQEDSVTLTCRGTHSPESdSIQWFHNGNLIPTHTQPSYRFKANN----------NDSGEYTCQ 114
Cdd:pfam13927   1 KP--VITVSPSSVTVREGETVTLTCEATGSPPP-TITWYKNGEPISSGSTRSRSLSGSNstltisnvtrSDAGTYTCV 75

Immunoglobulin (Ig)-like domain found in Leukocyte Ig-like receptors, Natural killer inhibitory receptors (KIRs) and similar domains; member of Immunoglobulin Constant-2 set of IgSF domains; The members here are composed of the first and second immunoglobulin (Ig)-like domains found in Leukocyte Ig-like receptors (LILRs), Natural killer inhibitory receptors (KIRs, also known as also known as cluster of differentiation (CD) 158), and similar proteins. This group includes LILRB1 (also known as LIR-1), LILRA5 (also known as LIR9), an activating natural cytotoxicity receptor NKp46, the immune-type receptor glycoprotein VI (GPVI), and the IgA-specific receptor Fc-alphaRI (also known as cluster of differentiation (CD) 89). LILRs are a family of immunoreceptors expressed on expressed on T and B cells, on monocytes, dendritic cells, and subgroups of natural killer (NK) cells. The human LILR family contains nine proteins (LILRA1-3, and 5, and LILRB1-5). From functional assays, and as the cytoplasmic domains of various LILRs, for example LILRB1, LILRB2 (also known as LIR-2), and LILRB3 (also known as LIR-3) contain immunoreceptor tyrosine-based inhibitory motifs (ITIMs), it is thought that LIR proteins are inhibitory receptors. Of the eight LIR family proteins, only LILRB1, and LILRB2, show detectable binding to class I MHC molecules; ligands for the other members have yet to be determined. The extracellular portions of the different LIR proteins contain different numbers of Ig-like domains for example, four in the case of LILRB1, and LILRB2, and two in the case of LILRB4 (also known as LIR-5). The activating natural cytotoxicity receptor NKp46 is expressed in natural killer cells, and is organized as an extracellular portion having two Ig-like extracellular domains, a transmembrane domain, and a small cytoplasmic portion. GPVI, which also contains two Ig-like domains, participates in the processes of collagen-mediated platelet activation and arterial thrombus formation. Fc-alphaRI is expressed on monocytes, eosinophils, neutrophils, and macrophages; it mediates IgA-induced immune effector responses such as phagocytosis, antibody-dependent cell-mediated cytotoxicity and respiratory burst. Killer cell immunoglobulin-like receptors (KIRs; also known as CD158 for human KIR) are transmembrane glycoproteins expressed by natural killer cells and subsets of T cells. KIRs are a family of highly polymorphic activating and inhibitory receptors that serve as key regulators of human NK cell function. The KIR proteins are classified by the number of extracellular immunoglobulin domains (2D or 3D) and by whether they have a long (L) or short (S) cytoplasmic domain. KIR proteins with the long cytoplasmic domain transduce inhibitory signals upon ligand binding via an immune tyrosine-based inhibitory motif (ITIM), while KIR proteins with the short cytoplasmic domain lack the ITIM motif and instead associate with the TYRO protein tyrosine kinase binding protein to transduce activating signals. The major ligands for KIR are MHC class I (HLA-A, -B or -C) molecules.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741  61 VLQEDSVTLTCRGThsPESDSIQWFHNGNLIPTHTQ--PSYRFKAN-------NNDSGEYTCQ----TGQTSLSDPVHLT 127
Cdd:cd16843    12 VPLGENVTIRCQGP--PEAVLFQLYKEGNSLSQGTVreKEPQNKAEfyiphmdRNHAGRYRCRyrsgTLWSEPSDPLELV 89

                  .
gi 1883684741 128 V 128
Cdd:cd16843    90 V 90

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

                          10        20        30        40        50        60
                  ....*....|....*....|....*....|....*....|....*....|....*....|...
gi 1883684741  61 VLQEDSVTLTCRGTHSPESDsIQWFHNGNLIPTHTQpSYRFKANNN----------DSGEYTC 113
Cdd:cd20970    14 AREGENATFMCRAEGSPEPE-ISWTRNGNLIIEFNT-RYIVRENGTtltirnirrsDMGIYLC 74

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

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741  61 VLQEDSVTLTCrgthSPES--DSIQWFHNGNLIPTHtqPSYRFKANN----------NDSGEYTCQTGQ---TSLSDPVH 125
Cdd:cd05740    12 VEDKDAVTLTC----EPETqnTSYLWWFNGQSLPVT--PRLTLSNGNrtltllnvtrEDAGAYQCEISNpvsANRSDPVT 85

                  ....
gi 1883684741 126 LTVL 129
Cdd:cd05740    86 LDVI 89

First immunoglobulin (Ig)-like domain found in Leukocyte Ig-like receptors (LILRs), Natural killer inhibitory receptors (KIRs) and similar domains; member of Immunoglobulin Constant-2 set of IgSF domains; The members here are composed of the first immunoglobulin (Ig)-like domain found in Leukocyte Ig-like receptors (LILRs) and Natural killer inhibitory receptors (KIRs, also known as also known as cluster of differentiation (CD) 158), and similar proteins. This group includes LILRB1 (also known as LIR-1), LILRA5 (also known as LIR9), an activating natural cytotoxicity receptor NKp46, the immune-type receptor glycoprotein VI (GPVI), and the IgA-specific receptor Fc-alphaRI (also known as cluster of differentiation (CD) 89). LILRs are a family of immunoreceptors expressed on expressed on T and B cells, on monocytes, dendritic cells, and subgroups of natural killer (NK) cells. The human LILR family contains nine proteins (LILRA1-3, and 5, and LILRB1-5). From functional assays, and as the cytoplasmic domains of various LILRs, for example LILRB1, LILRB2 (also known as LIR-2), and LILRB3 (also known as LIR-3) contain immunoreceptor tyrosine-based inhibitory motifs (ITIMs), it is thought that LIR proteins are inhibitory receptors. Of the eight LIR family proteins, only LILRB1, and LILRB2, show detectable binding to class I MHC molecules; ligands for the other members have yet to be determined. The extracellular portions of the different LIR proteins contain different numbers of Ig-like domains for example, four in the case of LILRB1, and LILRB2, and two in the case of LILRB4 (also known as LIR-5). The activating natural cytotoxicity receptor NKp46 is expressed in natural killer cells, and is organized as an extracellular portion having two Ig-like extracellular domains, a transmembrane domain, and a small cytoplasmic portion. GPVI, which also contains two Ig-like domains, participates in the processes of collagen-mediated platelet activation and arterial thrombus formation. Fc-alphaRI is expressed on monocytes, eosinophils, neutrophils, and macrophages; it mediates IgA-induced immune effector responses such as phagocytosis, antibody-dependent cell-mediated cytotoxicity and respiratory burst. Killer cell immunoglobulin-like receptors (KIRs; also known as CD158 for human KIR) are transmembrane glycoproteins expressed by natural killer cells and subsets of T cells. KIRs are a family of highly polymorphic activating and inhibitory receptors that serve as key regulators of human NK cell function. The KIR proteins are classified by the number of extracellular immunoglobulin domains (2D or 3D) and by whether they have a long (L) or short (S) cytoplasmic domain. KIR proteins with the long cytoplasmic domain transduce inhibitory signals upon ligand binding via an immune tyrosine-based inhibitory motif (ITIM), while KIR proteins with the short cytoplasmic domain lack the ITIM motif and instead associate with the TYRO protein tyrosine kinase binding protein to transduce activating signals. The major ligands for KIR are MHC class I (HLA-A, -B or -C) molecules.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 1883684741  61 VLQEDSVTLTCRGThsPESDSIQWFHNGNLIPTHTQPSYRFKA-------NNNDSGEYTCQ----TGQTSLSDPVHLTV 128
Cdd:cd05751    12 IPLEKSVTIRCQGT--PEAFLYQLEKEGNSTETVIPKKPQKKAefiiphmNSRTAGRYRCRyrkgAGWSEPSDLLELVV 88

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
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 1883684741  61 VLQEDSVTLTCRGTHSPESDSIQWFHNGNlipTHTQPSYRFKANN--------------NDSGEYTCQT 115
Cdd:pfam00047   8 VLEGDSATLTCSASTGSPGPDVTWSKEGG---TLIESLKVKHDNGrttqssllisnvtkEDAGTYTCVV 73

Fifth Ig-like domain of Roundabout (Robo) homolog 1/2, and similar domains; a member of the I-set of IgSF domains; The members here are composed of the fifth Ig-like domain of Roundabout (Robo) homolog 1/2 and similar domains. 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, -2, and -3), and three mammalian Slit homologs (Slit-1,-2, -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, -2, and -3 are expressed by commissural neurons in the vertebrate spinal cord and Slits 1, -2, -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 is the Ig1 domain, while the Ig2 domain has been proposed to harbor a weak secondary binding site. The fifth Ig-like domain of Robo 1 and 2 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. 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

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741  51 VLKLEPQWINVLQEDSVTLTCRGTHSPESdSIQWFHNGNLIPTH-----TQP--SYRFK-ANNNDSGEYTCQTGQTSLSD 122
Cdd:cd20952     1 IILQGPQNQTVAVGGTVVLNCQATGEPVP-TISWLKDGVPLLGKderitTLEngSLQIKgAEKSDTGEYTCVALNLSGEA 79

                  ....*.
gi 1883684741 123 PVHLTV 128
Cdd:cd20952    80 TWSAVL 85

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

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1883684741  51 VLKLEPQWINVLQEDSVTLTCRGTHSPESD-SIQWFHNGNLIP-----THTQPSYRFKANNN---------DSGEYTC-- 113
Cdd:cd04970     4 RITLAPSNADITVGENATLQCHASHDPTLDlTFTWSFNGVPIDlekieGHYRRRYGKDSNGDleivnaqlkHAGRYTCta 83

                          90
                  ....*....|....*
gi 1883684741 114 QTGQTSLSDPVHLTV 128
Cdd:cd04970    84 QTVVDSDSASATLVV 98

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|...
gi 1883684741 133 LVLQTPHLEFQEGETIVLRCHSwKDKPLVKVTFFQNGKSKKFSRSDP--------NFSIPQANHSHSGDYHCT 197
Cdd:pfam13927   4 ITVSPSSVTVREGETVTLTCEA-TGSPPPTITWYKNGEPISSGSTRSrslsgsnsTLTISNVTRSDAGTYTCV 75

Fifth 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 fifth 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
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 1883684741  80 DSIQWFHNGNLIPTHtqpsYRFKANNN------------DSGEYTC----QTGQTSLSDpVHLTV 128
Cdd:cd20958    30 SSITWEKDGRRLPLN----HRQRVFPNgtlvienvqrssDEGEYTCtarnQQGQSASRS-VFVKV 89