immunoglobulin C2-set domain

{{Pfam_box

| Symbol = C2-set

| Name = Immunoglobulin C2-set domain

| image =

| width =

| caption =

| Pfam= PF05790

| InterPro= IPR008424

| SMART=

| Prosite =

| SCOP =

| TCDB =

| OPM family=

| OPM protein=

| PDB=

{{PDB3|1wip}}A:317–388 {{PDB3|1wiq}}B:317–388 {{PDB3|1wio}}B:317–388

{{PDB3|1cid}} :316–386 {{PDB3|1hng}}B:128–198 {{PDB3|1hnf}} :135–205

{{PDB3|1rzk}}C:125–203 {{PDB3|1gc1}}C:125–203 {{PDB3|1cdi}} :125–203

{{PDB3|2b4c}}C:125–203 {{PDB3|1g9n}}C:125–203 {{PDB3|1cdu}} :125–203

{{PDB3|1rzj}}C:125–203 {{PDB3|1jl4}}D:125–203 {{PDB3|1opw}}C:125–203

{{PDB3|1cdy}} :125–203 {{PDB3|1cdj}} :125–203 {{PDB3|3cd4}} :125–203

{{PDB3|1opt}}C:125–203 {{PDB3|1cdh}} :125–203 {{PDB3|1g9m}}C:125–203

{{PDB3|1opn}}C:125–203 {{PDB3|1vca}}A:133–221 {{PDB3|1ij9}}A:133–220

{{PDB3|1vsc}}A:133–219

}}

The basic structure of immunoglobulin (Ig) molecules is a tetramer of two light chains and two heavy chains linked by disulphide bonds. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). There are five types of heavy chains: alpha, delta, epsilon, gamma and mu, all consisting of a variable domain (VH) and three (in alpha, delta and gamma) or four (in epsilon and mu) constant domains (CH1 to CH4). Ig molecules are highly modular proteins, in which the variable and constant domains have clear, conserved sequence patterns. The domains in Ig and Ig-like molecules are grouped into four types: V-set (variable; {{InterPro|IPR013106}}), C1-set (constant-1; {{InterPro|IPR003597}}), C2-set (constant-2; {{InterPro|IPR008424}}) and I-set (intermediate; {{InterPro|IPR013098}}).{{cite journal |vauthors=Smith DK, Xue H |title=Sequence profiles of immunoglobulin and immunoglobulin-like domains |journal=J. Mol. Biol. |volume=274 |issue=4 |pages=530–545 |year=1997 |pmid=9417933 |doi=10.1006/jmbi.1997.1432}} Structural studies have shown that these domains share a common core Greek-key beta-sandwich structure, with the types differing in the number of strands in the beta-sheets as well as in their sequence patterns.{{cite journal |vauthors=Potapov V, Sobolev V, Edelman M, Kister A, Gelfand I |title=Protein-Protein Recognition: Juxtaposition of Domain and Interface Cores in Immunoglobulins and Other Sandwich-like Proteins |journal=J. Mol. Biol. |volume=342 |issue=2 |pages=665–679 |year=2004 |pmid=15327963 |doi=10.1016/j.jmb.2004.06.072}}{{cite journal |vauthors=Clarke J, Fowler SB |title=Mapping the folding pathway of an immunoglobulin domain: structural detail from Phi value analysis and movement of the transition state |journal=Structure |volume=9 |issue=5 |pages=355–366 |year=2001 |pmid=11377196 |doi=10.1016/S0969-2126(01)00596-2|doi-access=free }}

Immunoglobulin-like domains that are related in both sequence and structure can be found in several diverse protein

families. Ig-like domains are involved in a variety of functions, including cell–cell recognition, cell-surface receptors, muscle structure and the immune system.{{cite journal |vauthors=Chothia C, Teichmann SA |title=Immunoglobulin superfamily proteins in Caenorhabditis elegans |journal=J. Mol. Biol. |volume=296 |issue=5 |pages= 1367–83|year=2000 |pmid=10698639 |doi=10.1006/jmbi.1999.3497|citeseerx=10.1.1.327.6917 }}

C2-set domains, which are Ig-like domains resembling the antibody constant domain. C2-set domains are found primarily in the mammalian T-cell surface antigens CD2 (Cluster of Differentiation 2), CD4 and CD80, as well as in vascular (VCAM) and intercellular (ICAM) cell adhesion molecules.

CD2 mediates T-cell adhesion via its ectodomain, and signal transduction utilising its 117-amino acid cytoplasmic tail.{{cite journal |vauthors=Reinherz EL, Yang H |title=Dynamic recruitment of human CD2 into lipid rafts. Linkage to T cell signal transduction |journal=J. Biol. Chem. |volume=276 |issue=22 |pages=18775–18785 |year=2001 |pmid=11376005 | doi=10.1074/jbc.M009852200|doi-access=free }} CD2 displays structural and functional similarities with African swine fever virus (ASFV) LMW8-DR, a protein that is involved in cell–cell adhesion and immune response modulation, suggesting

a possible role in the pathogenesis of ASFV infection.{{cite journal |vauthors=Kutish GF, Rock DL, Afonso CL, Borca MV, Irusta P, Carrillo C, Brun A, Sussman M |title=An African swine fever virus gene with similarity to the T-lymphocyte surface antigen CD2 mediates hemadsorption |journal=Virology |volume=199 |issue=2 |pages=463–468 |year=1994 |pmid=7907198 |doi=10.1006/viro.1994.1146}} CD4 is the primary receptor for HIV-1. CD4 has four immunoglobulin-like domains in its extracellular region that share the same structure, but can differ in sequence. Certain extracellular domains may be involved in dimerisation.{{cite journal |author=Sanejouand YH |title=Domain swapping of CD4 upon dimerization |journal=Proteins |volume=57 |issue=1 |pages= 205–12|year=2004 |pmid=15326605 |doi=10.1002/prot.20197}}