Immunoglobulin Variable (IgV) domain Cluster of Differentiation (CD) 28; The members here are composed of the immunoglobulin variable region (IgV) of Cluster of Differentiation (CD) 28). CD28 is one of the proteins expressed on T cells that provide co-stimulatory signals required for T cell activation and survival. CD28 is the receptor for CD80 (B7.1) and CD86 (B7.2) proteins. CD28 consists of a paired V-set of immunoglobulin (Ig) superfamily domains attached to single-transmembrane domains and cytoplasmic domains that contain the MYPPY motif, which is involved in binding B7.1 or B7.2. CD28 is very similar to CTLA-4 (cytotoxic T-lymphocyte-associated protein 4, also known as CD152 (cluster of differentiation 152)), which is involved in the regulation of T cell response, acting as an inhibitor of intracellular signaling. CTLA-4 also binds the B7 molecules (B7.1 and B7.2) with a higher affinity than does CD28. The B7/CTLA-4 interaction generates inhibitory signals down-regulating the response, and may prevent T cell activation by weak TCR signals. CD28 and CTLA-4 then elicit opposing signals in the regulation of T cell responsiveness and homeostasis. The IgSF is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. The two sheets are linked together by a conserved disulfide bond between B strand and F strand. 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 N-terminal Ig-like domain of CD28 is a member of the V-set Ig domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C'-C" in the other. However, each CD28-B7 family member is slightly different, some have an IgV domain which lacks an A' or C" strand.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 351706933  23 MFTFHHGGVQVLCRYPE--IVQQFKMQLLRGKQI---LCDLNKTKGSGNKVFIQNQMFCQLQLSNSSVSFFLENFDSSHR 97
Cdd:cd20925    8 MLVVYNNAVNLSCKYTYnlFSKEFRASLHKGLDSaveVCVVYGNYSQQLQVYSNTGFNCDGKLGNESVTFYLWNLYVNQT 87

                         90
                 ....*....|....*
gi 351706933  98 GYYFCNISIFDPPPF 112
Cdd:cd20925   88 DIYFCKIEVMYPPPY 102

Immunoglobulin Variable (IgV) domain Cluster of Differentiation (CD) 28; The members here are composed of the immunoglobulin variable region (IgV) of Cluster of Differentiation (CD) 28). CD28 is one of the proteins expressed on T cells that provide co-stimulatory signals required for T cell activation and survival. CD28 is the receptor for CD80 (B7.1) and CD86 (B7.2) proteins. CD28 consists of a paired V-set of immunoglobulin (Ig) superfamily domains attached to single-transmembrane domains and cytoplasmic domains that contain the MYPPY motif, which is involved in binding B7.1 or B7.2. CD28 is very similar to CTLA-4 (cytotoxic T-lymphocyte-associated protein 4, also known as CD152 (cluster of differentiation 152)), which is involved in the regulation of T cell response, acting as an inhibitor of intracellular signaling. CTLA-4 also binds the B7 molecules (B7.1 and B7.2) with a higher affinity than does CD28. The B7/CTLA-4 interaction generates inhibitory signals down-regulating the response, and may prevent T cell activation by weak TCR signals. CD28 and CTLA-4 then elicit opposing signals in the regulation of T cell responsiveness and homeostasis. The IgSF is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. The two sheets are linked together by a conserved disulfide bond between B strand and F strand. 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 N-terminal Ig-like domain of CD28 is a member of the V-set Ig domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C'-C" in the other. However, each CD28-B7 family member is slightly different, some have an IgV domain which lacks an A' or C" strand.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 351706933  23 MFTFHHGGVQVLCRYPE--IVQQFKMQLLRGKQI---LCDLNKTKGSGNKVFIQNQMFCQLQLSNSSVSFFLENFDSSHR 97
Cdd:cd20925    8 MLVVYNNAVNLSCKYTYnlFSKEFRASLHKGLDSaveVCVVYGNYSQQLQVYSNTGFNCDGKLGNESVTFYLWNLYVNQT 87

                         90
                 ....*....|....*
gi 351706933  98 GYYFCNISIFDPPPF 112
Cdd:cd20925   88 DIYFCKIEVMYPPPY 102