Second immunoglobulin (Ig)-like domain of interleukin-1 receptor (IL1R), and similar domains; The members here are composed of the second immunoglobulin (Ig)-like domain of interleukin-1 receptor (IL1R; also known as cluster of differentiation (CD) 121). IL-1 alpha and IL-1 beta are cytokines which participate in the regulation of inflammation, immune responses, and hematopoiesis. These cytokines bind to the IL-1 receptor type 1 (IL1R1), which is activated on additional association with interleukin-1 receptor accessory protein (IL1RAP). IL-1 also binds a second receptor designated type II (IL1R2). Mature IL1R1 consists of three IG-like domains, a transmembrane domain, and a large cytoplasmic domain. Mature IL1R2 is organized similarly except that it has a short cytoplasmic domain. The latter does not initiate signal transduction. A naturally occurring cytokine IL-1RA (IL-1 receptor antagonist) is widely expressed and binds to IL-1 receptors, inhibiting the binding of IL-1 alpha and IL-1 beta. This group also contains ILIR-like 1 (IL1R1L) which maps to the same chromosomal location as IL1R1 and IL1R2.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6172225  118 MYSTVSGSEKNSKIYCPTIDLYNW---TAPLEWFKNCQALQG-SRYRAHKSFLVIDNVMTEDAGDYTCKFIHNENGANYS 193
Cdd:cd05757   2 RYKQKLPITKGGKITCPDLDDYKNenvLPPIQWYKDCKPLQGdKRFIPKGSKLLIQNVTEEDAGNYTCKFTYTHNGKQYN 81

                        90
                ....*....|.
gi 6172225  194 VTATRSFTVKV 204
Cdd:cd05757  82 VTRTISLTVTE 92

Second immunoglobulin (Ig)-like domain of interleukin-1 receptor (IL1R), and similar domains; The members here are composed of the second immunoglobulin (Ig)-like domain of interleukin-1 receptor (IL1R; also known as cluster of differentiation (CD) 121). IL-1 alpha and IL-1 beta are cytokines which participate in the regulation of inflammation, immune responses, and hematopoiesis. These cytokines bind to the IL-1 receptor type 1 (IL1R1), which is activated on additional association with interleukin-1 receptor accessory protein (IL1RAP). IL-1 also binds a second receptor designated type II (IL1R2). Mature IL1R1 consists of three IG-like domains, a transmembrane domain, and a large cytoplasmic domain. Mature IL1R2 is organized similarly except that it has a short cytoplasmic domain. The latter does not initiate signal transduction. A naturally occurring cytokine IL-1RA (IL-1 receptor antagonist) is widely expressed and binds to IL-1 receptors, inhibiting the binding of IL-1 alpha and IL-1 beta. This group also contains ILIR-like 1 (IL1R1L) which maps to the same chromosomal location as IL1R1 and IL1R2.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6172225  118 MYSTVSGSEKNSKIYCPTIDLYNW---TAPLEWFKNCQALQG-SRYRAHKSFLVIDNVMTEDAGDYTCKFIHNENGANYS 193
Cdd:cd05757   2 RYKQKLPITKGGKITCPDLDDYKNenvLPPIQWYKDCKPLQGdKRFIPKGSKLLIQNVTEEDAGNYTCKFTYTHNGKQYN 81

                        90
                ....*....|.
gi 6172225  194 VTATRSFTVKV 204
Cdd:cd05757  82 VTRTISLTVTE 92

IL-beta-binding protein; Provisional

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6172225    27 LENEALIVRCPR-----QGKPSYTVDWYY--SQTNKSIPTQERNRvfasgrLLKFLPAEvADSGIYTCIVRSPTFNRTGY 99
Cdd:PHA02785  39 LENEPVILPCPQintlsSGYNILDILWEKrgADNDRIIPIDNGSN------MLILNPTQ-SDSGIYICITKNETYCDMMS 111

                         90       100       110       120       130       140       150       160
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6172225   100 ANVTIYkKQSDCNVpDYLMYSTVSGSEKNSKIYCPTIDLY---NWTAPLEWfKNCQALQGSRYRAHK-SFLVIDNVMTED 175
Cdd:PHA02785 112 LNLTIV-SVSESNI-DLISYPQIVNERSTGEMVCPNINAFiasNVNADIIW-SGHRRLRNKRLKQRTpGIITIEDVRKND 188

                        170       180
                 ....*....|....*....|
gi 6172225   176 AGDYTCKFIHNENGANYSVT 195
Cdd:PHA02785 189 AGYYTCVLKYIYGDKTYNVT 208

Immunoglobulin I-set domain;

                          10        20        30        40        50        60
                  ....*....|....*....|....*....|....*....|....*....|....*....|....
gi 6172225    146 EWFKNCQAL-QGSRYRAHK----SFLVIDNVMTEDAGDYTCKfIHNENGanysvTATRSFTVKV 204
Cdd:pfam07679  33 SWFKDGQPLrSSDRFKVTYeggtYTLTISNVQPDDSGKYTCV-ATNSAG-----EAEASAELTV 90

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

                           10        20        30        40        50        60
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 6172225     145 LEWFKNCQAL--QGSRYRAHKS----FLVIDNVMTEDAGDYTCKFIhnengaNYSVTATRSFTVKV 204
Cdd:smart00410  26 VTWYKQGGKLlaESGRFSVSRSgstsTLTISNVTPEDSGTYTCAAT------NSSGSASSGTTLTV 85

Second immunoglobulin (Ig)-like domain of interleukin-1 receptor (IL1R), and similar domains; The members here are composed of the second immunoglobulin (Ig)-like domain of interleukin-1 receptor (IL1R; also known as cluster of differentiation (CD) 121). IL-1 alpha and IL-1 beta are cytokines which participate in the regulation of inflammation, immune responses, and hematopoiesis. These cytokines bind to the IL-1 receptor type 1 (IL1R1), which is activated on additional association with interleukin-1 receptor accessory protein (IL1RAP). IL-1 also binds a second receptor designated type II (IL1R2). Mature IL1R1 consists of three IG-like domains, a transmembrane domain, and a large cytoplasmic domain. Mature IL1R2 is organized similarly except that it has a short cytoplasmic domain. The latter does not initiate signal transduction. A naturally occurring cytokine IL-1RA (IL-1 receptor antagonist) is widely expressed and binds to IL-1 receptors, inhibiting the binding of IL-1 alpha and IL-1 beta. This group also contains ILIR-like 1 (IL1R1L) which maps to the same chromosomal location as IL1R1 and IL1R2.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6172225  118 MYSTVSGSEKNSKIYCPTIDLYNW---TAPLEWFKNCQALQG-SRYRAHKSFLVIDNVMTEDAGDYTCKFIHNENGANYS 193
Cdd:cd05757   2 RYKQKLPITKGGKITCPDLDDYKNenvLPPIQWYKDCKPLQGdKRFIPKGSKLLIQNVTEEDAGNYTCKFTYTHNGKQYN 81

                        90
                ....*....|.
gi 6172225  194 VTATRSFTVKV 204
Cdd:cd05757  82 VTRTISLTVTE 92

First immunoglobulin (Ig)-like domain of interleukin-1 receptor (IL1R), and similar domains; The members here are composed of the first immunoglobulin (Ig)-like domain of interleukin-1 receptor (IL1R; also known as cluster of differentiation (CD) 121). IL-1 alpha and IL-1 beta are cytokines which participate in the regulation of inflammation, immune responses, and hematopoiesis. These cytokines bind to the IL-1 receptor type 1 (IL1R1), which is activated on additional association with interleukin-1 receptor accessory protein (IL1RAP). IL-1 also binds a second receptor designated type II (IL1R2). Mature IL1R1 consists of three Ig-like domains, a transmembrane domain, and a large cytoplasmic domain. Mature IL1R2 is organized similarly except that it has a short cytoplasmic domain. The latter does not initiate signal transduction. A naturally occurring cytokine IL-1RA (IL-1 receptor antagonist) is widely expressed and binds to IL-1 receptors, inhibiting the binding of IL-1 alpha and IL-1 beta.

                        10        20        30        40        50        60        70
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 6172225   22 KQSWGLENEALIVRCPRQGKPS-----YTVDWYYSQTNKSIPTQERNRVFASGRLLKFLPAEVADSGIYTCIVRSPTF 94
Cdd:cd05756   8 KILVVLEGEPDVIKCPLFPNFLaqsagLNLTWYKNDSETPISFEPDSRIHQEKDKLWFVPALLEDSGNYYCVVRNSTY 85

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6172225      21 SKQSWGLENEALIVRCPRQGKPSYTVDWYYsQTNKSIPTQERNRVFASGRL--LKFLPAEVADSGIYTCIVRSPTFNRTG 98
Cdd:smart00410   1 PPSVTVKEGESVTLSCEASGSPPPEVTWYK-QGGKLLAESGRFSVSRSGSTstLTISNVTPEDSGTYTCAATNSSGSASS 79

                   ....*.
gi 6172225      99 YANVTI 104
Cdd:smart00410  80 GTTLTV 85

First immunoglobulin (Ig)-like domain of interleukin-1 receptor (IL1R), and similar domains; The members here are composed of the first immunoglobulin (Ig)-like domain of interleukin-1 receptor (IL1R). IL-1 alpha and IL-1 beta are cytokines which participate in the regulation of inflammation, immune responses, and hematopoiesis. These cytokines bind to the IL-1 receptor type 1 (IL1R1), which is activated on additional association with interleukin-1 receptor accessory protein (IL1RAP). IL-1 also binds a second receptor designated type II (IL1R2). Mature IL1R1 consists of three Ig-like domains, a transmembrane domain, and a large cytoplasmic domain. Mature IL1R2 is organized similarly except that it has a short cytoplasmic domain. The latter does not initiate signal transduction. IL-1 receptor antagonist (IL-1RA), a naturally occurring cytokine, is widely expressed and binds to IL-1 receptors, inhibiting the binding of IL-1 alpha and IL-1 beta.

                        10        20        30        40        50        60
                ....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 6172225   28 ENEALIVRCPRQGKPSY-TVDWYYSQTNKSIPTQERNRVFASGRLLKFLPAEVADSGIYTCIVRSPTF 94
Cdd:cd20991  13 ANEIDVRSCPLNPNESKgTITWYKNDSKTPISMEQDSRIHQYKEKLWFVPAKVEDSGHYYCVVRNSTY 80

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 6172225   18 AKFSKQSWGLENEALIVRCPRQGKPSYTVDWYySQTNKSIPTQERNRVFASGRLlKFLPAEVADSGIYTCIVRSPTFNRT 97
Cdd:cd05764   4 TRHTHELRVLEGQRATLRCKARGDPEPAIHWI-SPEGKLISNSSRTLVYDNGTL-DILITTVKDTGAFTCIASNPAGEAT 81

                ....*..
gi 6172225   98 GYANVTI 104
Cdd:cd05764  82 ARVELHI 88

Immunoglobulin (Ig) constant domain of the complement receptor of the immunoglobulin superfamily (CRIg); The members here are composed of the Immunoglobulin (Ig) constant domain of the complement receptor of the immunoglobulin superfamily (CRIg). The N-terminal domain of CRIg (also referred to as Z39Ig and V-set and Ig domain-containing 4 (VSIG4)) belongs to the IgV family of immunoglobulin-like domains while the C-terminal domain of CRIg belongs to the IgC family of immunoglobulin-like domains. CRIg plays a role in the complement system, an inhibitor of the alternative pathway convertases, and a negative regulator of T cell activation. 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 such as T-cell receptors, CD2, CD4, CD8, and membrane glycoproteins such as 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.

                        10        20        30        40        50
                ....*....|....*....|....*....|....*....|....*....|....*..
gi 6172225   34 VRCPRQGKPSYTVDWYYSQTNKSIPTQernrVFASGRLLkFLPAEVADSGIYTCIVR 90
Cdd:cd16082  18 LQCQAWGSPPISYVWYKEQTNNQEPIK----VAALSTLL-FKPAVVADSGSYFCTAK 69

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

                        10        20        30        40        50        60
                ....*....|....*....|....*....|....*....|....*....|....*....|
gi 6172225  147 WFKNCQALQGSRYRA--HKSFLVIDNVMTEDAGDYTCKfIHNENGANYSvtatrSFTVKV 204
Cdd:cd20978  35 WLHNGKPLQGPMERAtvEDGTLTIINVQPEDTGYYGCV-ATNEIGDIYT-----ETLLHV 88

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        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6172225   28 ENEALIVRCPRQGK-PSYTVDWYY--SQTNKSIPTQERNRVFASGRLLKFLPAEVADSGIYTCIVRSPTFNRTGYANVTI 104
Cdd:cd05750  13 EGSKLVLKCEATSEnPSPRYRWFKdgKELNRKRPKNIKIRNKKKNSELQINKAKLEDSGEYTCVVENILGKDTVTGNVTV 92

Third immunoglobulin (Ig)-like domain of hemolin, and similar domains; a member of the I-set of IgSF domains; The members here are composed of the third immunoglobulin (Ig)-like domain of hemolin and similar proteins. Hemolin, an insect immunoglobulin superfamily (IgSF) member containing four Ig-like domains, is a lipopolysaccharide-binding immune protein induced during bacterial infection. Hemolin shares significant sequence similarity with the first four Ig-like domains of the transmembrane cell adhesion molecules (CAMs) of the L1 family. IgSF domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. The third Ig-like domain of hemolin is a member of the I-set Ig domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. Like the V-set 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, including vascular (VCAM), intercellular (ICAM), neural (NCAM) and mucosal addressin (MADCAM) cell adhesion molecules, as well as junction adhesion molecules (JAM).

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6172225  113 VPDYLMYSTVSGSEKNSKIYCPTIDlyNWTAPLEWFKNCQALQG---SRYRAHKSF----LVIDNVMTEDAGDYTCKFih 185
Cdd:cd20977   2 VPQYVSKDMMAKAGDVTMIYCMYGS--NPTAHPNYFKNGKDVNGnpeDRITRHNRTsgkrLLFKTTLPEDEGVYTCEV-- 77

                        90
                ....*....|....*....
gi 6172225  186 nENGANYsvTATRSFTVKV 204
Cdd:cd20977  78 -DNGVGK--PQKHSLKLTV 93

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60
                  ....*....|....*....|....*....|....*....|....*....|....*....|....
gi 6172225     27 LENEALIVRCPRQGKPSYTVDWYYSQTNKSIPTQERNRVFASGRLLKFLPAEVADSGIYTCIVR 90
Cdd:pfam13927  14 REGETVTLTCEATGSPPPTITWYKNGEPISSGSTRSRSLSGSNSTLTISNVTRSDAGTYTCVAS 77

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

                        10        20        30        40        50        60
                ....*....|....*....|....*....|....*....|....*....|....*....|...
gi 6172225  147 WFKNCQALQGS-RYRAHK----SFLVIDNVMTEDAGDYTCKfIHNENGanysvTATRSFTVKV 204
Cdd:cd05748  26 WSKDGQPLKETgRVQIETtassTSLVIKNAKRSDSGKYTLT-LKNSAG-----EKSATINVKV 82

Second immunoglobulin (Ig)-like domain of fibroblast growth factor (FGF) receptor_like-1(FGFRL1); 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 like-1(FGFRL1). FGFRL1 is comprised of a signal peptide, three extracellular Ig-like modules, a transmembrane segment, and a short intracellular domain. FGFRL1 is expressed preferentially in skeletal tissues. Similar to FGF receptors, the expressed protein interacts specifically with heparin and with FGF2. FGFRL1 does not have a protein tyrosine kinase domain at its C-terminus; neither does its cytoplasmic domain appear to interact with a signaling partner. It has been suggested that FGFRL1 may not have any direct signaling function, but instead acts as a decoy receptor trapping FGFs and preventing them from binding other receptors.

                        10        20        30        40        50        60        70
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|...
gi 6172225   34 VRCPRQGKPSYTVDWYYSQTNKSIPTQERNRVFASGRLLKFLPAEvaDSGIYTCIVrsptFNRTGYANVTiYK 106
Cdd:cd05856  24 LKCVASGNPRPDITWLKDNKPLTPPEIGENKKKKWTLSLKNLKPE--DSGKYTCHV----SNRAGEINAT-YK 89

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 6172225  147 WFKNCQAL-QGSRYRAHKS-FLVIDNV-MTEDAGDYTCKfIHNENGanysVTATRSFTVKV 204
Cdd:cd20958  34 WEKDGRRLpLNHRQRVFPNgTLVIENVqRSSDEGEYTCT-ARNQQG----QSASRSVFVKV 89