Second immunoglobulin domain of Cluster of Differentiation (CD) 33 and related Siglecs; member of the C2-set of IgSF domains; The members here are composed of the second immunoglobulin (Ig) domain of Cluster of Differentiation (CD) 33 (also known as sialic-acid binding immunoglobulin type-lectin 3 (Siglec-3)) and related Siglecs. CD33, a Siglec family member, is a well-known immunotherapeutic target in acute myeloid leukemia (AML). It is an inhibitory sialoadhesin expressed in human leukocytes of the myeloid lineage and some lymphoid subsets, including natural killer (NK) cells. Siglecs are primarily expressed on immune cells and recognize sialic acid-containing glycan ligands. Siglecs are organized as an extracellular module composed of Ig-like domains (an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains), followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG (Siglec-4, myelin-associated glycoprotein), the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11. CD33 (Siglec-3) is the smallest Siglec member. It preferentially binds to alpha2-6- and alpha2-3-sialylated glycans and strongly binds to sialylated ligands on leukemic cell lines. 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. This group includes CD33-related Siglecs which belong to the C2-set of IgSF domains. Unlike the C1-set, the C2-set structures do not have a D strand.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 141 PNIVVPPEVVAGTEVEVSCMVPDNCPELRPELSWLGHEGLGEPAVLGRlREDEGTWVQVSLLHFVPTREANGHRLGCQAS 220
Cdd:cd20987   1 PNIHVPEELEAGQEVTLTCSVPDNCPALSPEFSWLGAALTPLPPVLGR-LEEEGTTTHSSVLTFTPRPEDHGTNLTCQVK 79

                        90
                ....*....|....*
gi 11225258 221 FPNTTLQFEGYASMD 235
Cdd:cd20987  80 FPGATVTTERTIQLN 94

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258    333 GTMVAVEGETVSILCSTQSNPDPILTIFKEKQIL-------STVIYESELQLELPAVSPEDDGEYWCVAENQYGQRATAF 405
Cdd:smart00410   2 PSVTVKEGESVTLSCEASGSPPPEVTWYKQGGKLlaesgrfSVSRSGSTSTLTISNVTPEDSGTYTCAATNSSGSASSGT 81

                   ....
gi 11225258    406 NLSV 409
Cdd:smart00410  82 TLTV 85

Second immunoglobulin domain of Cluster of Differentiation (CD) 33 and related Siglecs; member of the C2-set of IgSF domains; The members here are composed of the second immunoglobulin (Ig) domain of Cluster of Differentiation (CD) 33 (also known as sialic-acid binding immunoglobulin type-lectin 3 (Siglec-3)) and related Siglecs. CD33, a Siglec family member, is a well-known immunotherapeutic target in acute myeloid leukemia (AML). It is an inhibitory sialoadhesin expressed in human leukocytes of the myeloid lineage and some lymphoid subsets, including natural killer (NK) cells. Siglecs are primarily expressed on immune cells and recognize sialic acid-containing glycan ligands. Siglecs are organized as an extracellular module composed of Ig-like domains (an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains), followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG (Siglec-4, myelin-associated glycoprotein), the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11. CD33 (Siglec-3) is the smallest Siglec member. It preferentially binds to alpha2-6- and alpha2-3-sialylated glycans and strongly binds to sialylated ligands on leukemic cell lines. 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. This group includes CD33-related Siglecs which belong to the C2-set of IgSF domains. Unlike the C1-set, the C2-set structures do not have a D strand.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 141 PNIVVPPEVVAGTEVEVSCMVPDNCPELRPELSWLGHEGLGEPAVLGRlREDEGTWVQVSLLHFVPTREANGHRLGCQAS 220
Cdd:cd20987   1 PNIHVPEELEAGQEVTLTCSVPDNCPALSPEFSWLGAALTPLPPVLGR-LEEEGTTTHSSVLTFTPRPEDHGTNLTCQVK 79

                        90
                ....*....|....*
gi 11225258 221 FPNTTLQFEGYASMD 235
Cdd:cd20987  80 FPGATVTTERTIQLN 94

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258    333 GTMVAVEGETVSILCSTQSNPDPILTIFKEKQIL-------STVIYESELQLELPAVSPEDDGEYWCVAENQYGQRATAF 405
Cdd:smart00410   2 PSVTVKEGESVTLSCEASGSPPPEVTWYKQGGKLlaesgrfSVSRSGSTSTLTISNVTPEDSGTYTCAATNSSGSASSGT 81

                   ....
gi 11225258    406 NLSV 409
Cdd:smart00410  82 TLTV 85

Fourth Ig-like domain from smooth muscle myosin light chain kinase and similar domains ; a member of the I-set of IgSF domains; The members here are composed of the fourth immunoglobulin (Ig)-like domain from smooth muscle myosin light chain kinase (MYLK) and similar domains. 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 this group shows that the fourth Ig-like domain from myosin light chain kinase lacks this strand and thus 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        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 239 PPVIVEMNSSVEAIEGSHVSLLCGADSNPPPLLTWMRDGTVLREAVAESLLLELE------EVTPAEDGVYACLAENAYG 312
Cdd:cd20976   1 APSFSSVPKDLEAVEGQDFVAQCSARGKPVPRITWIRNAQPLQYAADRSTCEAGVgelhiqDVLPEDHGTYTCLAKNAAG 80

                        90
                ....*....|
gi 11225258 313 QDNRTVGLSV 322
Cdd:cd20976  81 QVSCSAWVTV 90

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258    247 SSVEAIEGSHVSLLCGADSNPPPLLTWMRDGTVL-----REAVAESLLLEL---EEVTPAEDGVYACLAENAYGQDNRTV 318
Cdd:smart00410   2 PSVTVKEGESVTLSCEASGSPPPEVTWYKQGGKLlaesgRFSVSRSGSTSTltiSNVTPEDSGTYTCAATNSSGSASSGT 81

                   ....
gi 11225258    319 GLSV 322
Cdd:smart00410  82 TLTV 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 11225258     27 PSSISAFEGTCVSIPCRFDFPDElrpavVHGVWYFNSPypknyPPVVFKSRTQVVHESFqgrsrllgdlglrNCTLLLSN 106
Cdd:smart00410   1 PPSVTVKEGESVTLSCEASGSPP-----PEVTWYKQGG-----KLLAESGRFSVSRSGS-------------TSTLTISN 57

                           90
                   ....*....|
gi 11225258    107 VSPELGGKYY 116
Cdd:smart00410  58 VTPEDSGTYT 67

Second immunoglobulin domain of Cluster of Differentiation (CD) 33 and related Siglecs; member of the C2-set of IgSF domains; The members here are composed of the second immunoglobulin (Ig) domain of Cluster of Differentiation (CD) 33 (also known as sialic-acid binding immunoglobulin type-lectin 3 (Siglec-3)) and related Siglecs. CD33, a Siglec family member, is a well-known immunotherapeutic target in acute myeloid leukemia (AML). It is an inhibitory sialoadhesin expressed in human leukocytes of the myeloid lineage and some lymphoid subsets, including natural killer (NK) cells. Siglecs are primarily expressed on immune cells and recognize sialic acid-containing glycan ligands. Siglecs are organized as an extracellular module composed of Ig-like domains (an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains), followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG (Siglec-4, myelin-associated glycoprotein), the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11. CD33 (Siglec-3) is the smallest Siglec member. It preferentially binds to alpha2-6- and alpha2-3-sialylated glycans and strongly binds to sialylated ligands on leukemic cell lines. 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. This group includes CD33-related Siglecs which belong to the C2-set of IgSF domains. Unlike the C1-set, the C2-set structures do not have a D strand.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 141 PNIVVPPEVVAGTEVEVSCMVPDNCPELRPELSWLGHEGLGEPAVLGRlREDEGTWVQVSLLHFVPTREANGHRLGCQAS 220
Cdd:cd20987   1 PNIHVPEELEAGQEVTLTCSVPDNCPALSPEFSWLGAALTPLPPVLGR-LEEEGTTTHSSVLTFTPRPEDHGTNLTCQVK 79

                        90
                ....*....|....*
gi 11225258 221 FPNTTLQFEGYASMD 235
Cdd:cd20987  80 FPGATVTTERTIQLN 94

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258    333 GTMVAVEGETVSILCSTQSNPDPILTIFKEKQIL-------STVIYESELQLELPAVSPEDDGEYWCVAENQYGQRATAF 405
Cdd:smart00410   2 PSVTVKEGESVTLSCEASGSPPPEVTWYKQGGKLlaesgrfSVSRSGSTSTLTISNVTPEDSGTYTCAATNSSGSASSGT 81

                   ....
gi 11225258    406 NLSV 409
Cdd:smart00410  82 TLTV 85

Fourth Ig-like domain from smooth muscle myosin light chain kinase and similar domains ; a member of the I-set of IgSF domains; The members here are composed of the fourth immunoglobulin (Ig)-like domain from smooth muscle myosin light chain kinase (MYLK) and similar domains. 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 this group shows that the fourth Ig-like domain from myosin light chain kinase lacks this strand and thus 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        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 239 PPVIVEMNSSVEAIEGSHVSLLCGADSNPPPLLTWMRDGTVLREAVAESLLLELE------EVTPAEDGVYACLAENAYG 312
Cdd:cd20976   1 APSFSSVPKDLEAVEGQDFVAQCSARGKPVPRITWIRNAQPLQYAADRSTCEAGVgelhiqDVLPEDHGTYTCLAKNAAG 80

                        90
                ....*....|
gi 11225258 313 QDNRTVGLSV 322
Cdd:cd20976  81 QVSCSAWVTV 90

Immunoglobulin I-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258   240 PVIVEMNSSVEAIEGSHVSLLCGADSNPPPLLTWMRDGTVLRE-------AVAESLLLELEEVTPAEDGVYACLAENAYG 312
Cdd:pfam07679   1 PKFTQKPKDVEVQEGESARFTCTVTGTPDPEVSWFKDGQPLRSsdrfkvtYEGGTYTLTISNVQPDDSGKYTCVATNSAG 80

                          90
                  ....*....|
gi 11225258   313 QDNRTVGLSV 322
Cdd:pfam07679  81 EAEASAELTV 90

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258    247 SSVEAIEGSHVSLLCGADSNPPPLLTWMRDGTVL-----REAVAESLLLEL---EEVTPAEDGVYACLAENAYGQDNRTV 318
Cdd:smart00410   2 PSVTVKEGESVTLSCEASGSPPPEVTWYKQGGKLlaesgRFSVSRSGSTSTltiSNVTPEDSGTYTCAATNSSGSASSGT 81

                   ....
gi 11225258    319 GLSV 322
Cdd:smart00410  82 TLTV 85

Immunoglobulin (Ig)-like domain of human titin C terminus and similar proteins; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the fifth immunoglobulin (Ig)-like domain from the C-terminus of human titin x and similar proteins. Titin (also called connectin) is a fibrous sarcomeric protein specifically found in vertebrate striated muscle. Titin is gigantic; 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 and appears to function similar to an elastic band, keeping the myosin filaments centered in the sarcomere during muscle contraction or stretching. 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 11225258 334 TMVAVEGETVSILCSTQSNPDPILTIFKEKQILST----VIYESELQ--LELPAVSPEDDGEYWCVAENQYGQRATAFNL 407
Cdd:cd05747  12 SLTVSEGESARFSCDVDGEPAPTVTWMREGQIIVSsqrhQITSTEYKstFEISKVQMSDEGNYTVVVENSEGKQEAQFTL 91

                .
gi 11225258 408 S 408
Cdd:cd05747  92 T 92

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        70
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 11225258 335 MVAVEGETVSILCSTQSNPDPILTIFKEKQILSTVIYESELQ---LELPAVSPEDDGEYWCVAENQYGQRATAFNLSV 409
Cdd:cd20978  11 VVVKGGQDVTLPCQVTGVPQPKITWLHNGKPLQGPMERATVEdgtLTIINVQPEDTGYYGCVATNEIGDIYTETLLHV 88

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 11225258 329 PTVNGTMVAVEGETVSILCSTQSNPDPILTIFKEKQILST-----VIYESELQLELPAVSPEDDGEYWCVAEN 396
Cdd:cd20970   6 PQPSFTVTAREGENATFMCRAEGSPEPEISWTRNGNLIIEfntryIVRENGTTLTIRNIRRSDMGIYLCIASN 78

Third immunoglobulin (Ig)-like domain of Neural Cell Adhesion Molecule 1 (NCAM-1); member of the I-set of IgSF domains; The members here are composed of the third immunoglobulin (Ig)-like domain of Neural Cell Adhesion Molecule (NCAM-1). NCAM plays important roles in the development and regeneration of the central nervous system, in synaptogenesis and neural migration. NCAM mediates cell-cell and cell-substratum recognition and adhesion via homophilic (NCAM-NCAM), and heterophilic (NCAM-non-NCAM), interactions. NCAM is expressed as three major isoforms having different intracellular extensions. The extracellular portion of NCAM has five N-terminal Ig-like domains and two fibronectin type III domains. The double zipper adhesion complex model for NCAM homophilic binding involves Ig1, Ig2, and Ig3. By this model, Ig1 and Ig2 mediate dimerization of NCAM molecules situated on the same cell surface (cis interactions), and Ig3 domains mediate interactions between NCAM molecules expressed on the surface of opposing cells (trans interactions) through binding to the Ig1 and Ig2 domains. The adhesive ability of NCAM is modulated by the addition of polysialic acid chains to the fifth Ig-like domain.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 239 PPVIVEMNSSVEAIE--GSHVSLLCGADSNPPPLLTWMRDGTVLREAVAESL------LLELEEVTPAEDGVYACLAENA 310
Cdd:cd05730   1 PPTIRARQSEVNATAnlGQSVTLACDADGFPEPTMTWTKDGEPIESGEEKYSfnedgsEMTILDVDKLDEAEYTCIAENK 80

                        90
                ....*....|..
gi 11225258 311 YGQDNRTVGLSV 322
Cdd:cd05730  81 AGEQEAEIHLKV 92

Fourth immunoglobulin (Ig)-like domain of peroxidasin; The members here are composed of the fourth immunoglobulin (Ig)-like domain in peroxidasin. Peroxidasin has a peroxidase domain and interacting extracellular motifs containing four Ig-like domains. It has been suggested that peroxidasin is secreted, and has functions related to the stabilization of the extracellular matrix. It may play a part in various other important processes such as removal and destruction of cells which have undergone programmed cell death and protection of the organism against non-self.

                        10        20        30        40        50        60
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 11225258 343 VSILCSTQSNPDPILTIFKEK-QILSTVIYE--SELQLELPAVSPEDDGEYWCVAENQYGQRATAFNLS 408
Cdd:cd05746   1 VQIPCSAQGDPEPTITWNKDGvQVTESGKFHisPEGYLAIRDVGVADQGRYECVARNTIGYASVSMVLS 69

Second Ig-like domain of the giant muscle protein titin Z1z2 in the sarcomeric Z-disk, and similar domains; a member of the I-set of IgSF domains; The members here are composed of the second immunoglobulin (Ig)-like domain of the giant muscle protein titin Z1z2 in the sarcomeric Z-disk and similar proteins. Titin is a key component in the assembly and functioning of vertebrate striated muscles. By providing connections at the level of individual microfilaments, it contributes to the fine balance of forces between the two halves of the sarcomere. The Ig superfamily (IgSF) is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. IgSF domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. Unlike the V-set, one of the distinctive features of I-set domains is the lack of a C" strand. The structure of the titin Z1z2 lacks this strand and thus it belongs to the I-set of the IgSF. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the hemolymph protein hemolin, the muscle proteins titin, telokin, and twitchin, the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D that is involved in axonal guidance, immune function and angiogenesis.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 239 PPVIVEMNSSVEAIEGSHVSLLCGADSNPPPLLTWMRDGTVLREAVAESLLLELEEVT-------PAEDGVYACLAENAY 311
Cdd:cd20972   1 PPQFIQKLRSQEVAEGSKVRLECRVTGNPTPVVRWFCEGKELQNSPDIQIHQEGDLHSliiaeafEEDTGRYSCLATNSV 80

                        90
                ....*....|.
gi 11225258 312 GQDNRTVGLSV 322
Cdd:cd20972  81 GSDTTSAEIFV 91

Second immunoglobulin (Ig)-like domain of fibroblast growth factor (FGF) receptor, and similar domains; 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. This group also contains fibroblast growth factor (FGF) receptor like-1(FGFRL1). 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 11225258 340 GETVSILCSTQSNPDPILTIFKE----KQILSTVIYESELQ---LELPAVSPEDDGEYWCVAENQYGQRATAFNLSV 409
Cdd:cd05729  19 ANKVRLECGAGGNPMPNITWLKDgkefKKEHRIGGTKVEEKgwsLIIERAIPRDKGKYTCIVENEYGSINHTYDVDV 95

Third immunoglobulin (Ig) domain of contactin-1; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the third immunoglobulin (Ig) domain of the neural cell adhesion molecule contactin-1. Contactins are comprised of six Ig domains followed by four fibronectin type III (FnIII) domains anchored to the membrane by glycosylphosphatidylinositol. Contactin-1 is differentially expressed in tumor tissues and may through a RhoA mechanism, facilitate invasion and metastasis of human lung adenocarcinoma. This group belongs to the I-set of IgSF domains.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 239 PPVIVEMNSSVEAIEGSHVSLLCGADSNPPPLLTWMR-------------DGTVLReavaesllleLEEVTPAEDGVYAC 305
Cdd:cd05851   1 PADINVKFKDTYALKGQNVTLECFALGNPVPVIRWRKilepmpataeismSGAVLK----------IFNIQPEDEGTYEC 70

                ....*....
gi 11225258 306 LAENAYGQD 314
Cdd:cd05851  71 EAENIKGKD 79

Second immunoglobulin (Ig)-like domain of fibroblast growth factor (FGF) receptor, and similar domains; 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. This group also contains fibroblast growth factor (FGF) receptor like-1(FGFRL1). 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 11225258 254 GSHVSLLCGADSNPPPLLTWMRDGTVLREAVAESLLLELE--------EVTPAEDGVYACLAENAYGQDNRTVGLSV 322
Cdd:cd05729  19 ANKVRLECGAGGNPMPNITWLKDGKEFKKEHRIGGTKVEEkgwsliieRAIPRDKGKYTCIVENEYGSINHTYDVDV 95

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        70
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 11225258 254 GSHVSLLCGADSNPPPLLTWMRDGTVLRE--------AVAESLLLELEEVTPAEDGVYACLAENAYGQDNRTVGLSV 322
Cdd:cd05857  19 ANTVKFRCPAAGNPTPTMRWLKNGKEFKQehriggykVRNQHWSLIMESVVPSDKGNYTCVVENEYGSINHTYHLDV 95

Second immunoglobulin (Ig)-like domain of protein tyrosine kinase (PTK) 7; The members here are composed of the second immunoglobulin (Ig)-like domain in protein tyrosine kinase (PTK) 7, also known as CCK4. PTK7 is a subfamily of the receptor protein tyrosine kinase family, and is referred to as an RPTK-like molecule. RPTKs transduce extracellular signals across the cell membrane and play important roles in regulating cell proliferation, migration, and differentiation. PTK7 is organized as an extracellular portion having seven Ig-like domains, a single transmembrane region, and a cytoplasmic tyrosine kinase-like domain. PTK7 is considered a pseudokinase as it has several unusual residues in some of the highly conserved tyrosine kinase (TK) motifs; it is predicted to lack TK activity. PTK7 may function as a cell-adhesion molecule. PTK7 mRNA is expressed at high levels in placenta, melanocytes, liver, lung, pancreas, and kidney. PTK7 is overexpressed in several cancers, including melanoma and colon cancer lines.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 240 PVIVEMNSSVEAIE-GSHVSLLCGADSNPPPLLTWMRDGTVLREAVAESLLLELE------EVTPAEDGVYACLAENAYG 312
Cdd:cd05760   1 PVVLKHPASAAEIQpSSRVTLRCHIDGHPRPTYQWFRDGTPLSDGQGNYSVSSKErtltlrSAGPDDSGLYYCCAHNAFG 80

                        90
                ....*....|..
gi 11225258 313 Q--DNRTVGLSV 322
Cdd:cd05760  81 SvcSSQNFTLSI 92

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        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 240 PVIVEMNSSVEAIEGSHVSLLCGADSNPPPLLTWMRDGTVLREAVAESLLLEL--------EEVTPAEDGVYACLAENAY 311
Cdd:cd05744   1 PHFLQAPGDLEVQEGRLCRFDCKVSGLPTPDLFWQLNGKPVRPDSAHKMLVREngrhsliiEPVTKRDAGIYTCIARNRA 80

                ..
gi 11225258 312 GQ 313
Cdd:cd05744  81 GE 82

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 11225258   339 EGETVSILCS-TQSNPDPILTIFKEKQ--ILSTVIYESE-----LQLELPAVSPEDDGEYWCVAEN 396
Cdd:pfam00047  10 EGDSATLTCSaSTGSPGPDVTWSKEGGtlIESLKVKHDNgrttqSSLLISNVTKEDAGTYTCVVNN 75

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

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 334 TMVAVEGETVSILCSTQSNPDPILTIFKEKQILST--VIYESELQ-LELPAVSPEDDGEYWCVAENQYGQRATAFNLSVE 410
Cdd:cd05876   4 SLVALRGQSLVLECIAEGLPTPTVKWLRPSGPLPPdrVKYQNHNKtLQLLNVGESDDGEYVCLAENSLGSARHAYYVTVE 83

agrin-responsive second immunoglobulin-like domains (Ig2) of the Muscle-specific kinase (MuSK) ectodomain; a member of the I-set of Ig superfamily domains; The members here are composed of the second immunoglobulin-like (Ig) domains of the Muscle-specific kinase (MuSK) ectodomain. 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        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 236 VKYPPVivemnsSVEAIEGSHVSLLCGADSNPPPLLTWMRDGTVLRE----AVAESLLLELEEVTPAEDGVYACLAENAY 311
Cdd:cd20968   2 ITRPPT------NVTIIEGLKAVLPCTTMGNPKPSVSWIKGDDLIKEnnriAVLESGSLRIHNVQKEDAGQYRCVAKNSL 75

                .
gi 11225258 312 G 312
Cdd:cd20968  76 G 76

Third immunoglobulin (Ig)-like domain in Robo (roundabout) receptors; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the third immunoglobulin (Ig)-like domain in Robo (roundabout) receptors. Robo receptors play a role in the development of the central nervous system (CNS), and are receptors of Slit protein. Slit is a repellant secreted by the neural cells in the midline. Slit acts through Robo to prevent most neurons from crossing the midline from either side. Three mammalian Robo homologs (Robo1, Robo2, Robo3), and three mammalian Slit homologs (Slit-1,Slit-2, Slit-3), have been identified. Commissural axons, which cross the midline, express low levels of Robo; longitudinal axons, which avoid the midline, express high levels of Robo. Robo1, Robo2, and Robo3 are expressed by commissural neurons in the vertebrate spinal cord and Slit-1, Slit-2, and Slit-3 are expressed at the ventral midline. Robo-3 is a divergent member of the Robo family which instead of being a positive regulator of Slit responsiveness, antagonizes Slit responsiveness in precrossing axons. The Slit-Robo interaction is mediated by the second leucine-rich repeat (LRR) domain of Slit and the two N-terminal Ig domains of Robo, Ig1 and Ig2. The primary Robo binding site for Slit2 has been shown by surface plasmon resonance experiments and mutational analysis to be the Ig1 domain, while the Ig2 domain has been proposed to harbor a weak secondary binding site. This group belongs to the I-set of IgSF domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. Like the V-set Ig domains, members of the I-set have a discontinuous A strand, but lack a C" strand.

                        10        20        30        40        50        60        70
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 11225258 247 SSVEAIEGSHVSLLCGADSNPPPLLTWMRDGTVL---REAVAESLLLELEEVTPAEDGVYACLAENAYGQDNRTVGLSV 322
Cdd:cd05725   5 QNQVVLVDDSAEFQCEVGGDPVPTVRWRKEDGELpkgRYEILDDHSLKIRKVTAGDMGSYTCVAENMVGKIEASATLTV 83

Third immunoglobulin (Ig)-like domain of peroxidasin; The members here are composed of the third immunoglobulin (Ig)-like domain in peroxidasin. Peroxidasin has a peroxidase domain and interacting extracellular motifs containing four Ig-like domains. It has been suggested that peroxidasin is secreted and has functions related to the stabilization of the extracellular matrix. It may play a part in various other important processes such as removal and destruction of cells which have undergone programmed cell death and protection of the organism against non-self.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 339 EGETVSILCSTQSNPDPI---------LTIFKEKQILSTViyeselQLELPAVSPEDDGEYWCVAENQYGQRATAFNLSV 409
Cdd:cd05745   1 EGQTVDFLCEAQGYPQPViawtkggsqLSVDRRHLVLSSG------TLRISRVALHDQGQYECQAVNIVGSQRTVAQLTV 74

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        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 328 KPTVNgtMVAVEGETVSILCSTQSNPDPILTIFKEKQILS-----TVIYESE--LQLELPAVSPEDDGEYWCVAENQYGQ 400
Cdd:cd20973   2 QTLRD--KEVVEGSAARFDCKVEGYPDPEVKWMKDDNPIVesrrfQIDQDEDglCSLIISDVCGDDSGKYTCKAVNSLGE 79

                ....*....
gi 11225258 401 RATAFNLSV 409
Cdd:cd20973  80 ATCSAELTV 88

Third immunoglobulin domain of the hematopoietic colony-stimulating factor 1 receptor (CSF-1R), and similar domains; member of the I-set of IgSF domains; The members here are composed of the third immunoglobulin domain of the hematopoietic colony-stimulating factor 1 receptor (CSF-1R) and similar proteins. CSF-1R, a class III receptor tyrosine kinase (RTKIII), is critical to the survival, proliferation, and differentiation of mononuclear phagocytic cells such as monocytes, tissue macrophages, muscularis macrophages, microglia, osteoclasts, Paneth cells, and myeloid dendritic cells. Human colony-stimulating factor 1 receptor (hCSF-1R) is unique among the hematopoietic receptors because it is activated by two distinct cytokines, CSF-1 and interleukin-34 (IL-34). The Ig superfamily (IgSF) 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. IgSF domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. This group belongs to the I-set of IgSF domains.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 11225258 335 MVAVEGETVSILCSTqSNPDPILTIFKEKQILSTVI----------YESELQLELPAVSPEDDGEYWCVAENQYGQRATA 404
Cdd:cd20936  10 LVRIRGEAAQIVCSA-SNVDVNFDVFLQHGDTKLAIpqqsdfhdnrYQKVLTLNLDQVDFQDAGNYSCVASNVQGKHSAS 88

                ....*
gi 11225258 405 FNLSV 409
Cdd:cd20936  89 MFFRV 93

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 11225258 243 VEMNSSVEAIEGSHVSLLCGADSNPPPLLTWMRDGTVLREAVAESLLLELEE-------VTPAEDGVYACLAENAYGQDN 315
Cdd:cd20949   3 TENAYVTTVKEGQSATILCEVKGEPQPNVTWHFNGQPISASVADMSKYRILAdgllinkVTQDDTGEYTCRAYQVNSIAS 82

                ....*..
gi 11225258 316 RTVGLSV 322
Cdd:cd20949  83 DMQERTV 89