collagen a-1(iii) chain

Collagen alpha-1(III) chain（Col3a1） is a secreted protein and belongs to the fibrillar collagen family.It contains 1 fibrillar collagen NC1 domain and 1 VWFC domain. Collagen alpha-1(III) chain is a fibrillar collagen that is found in extensible connective tissues such as skin, lung, and the vascular system, frequently in association with type I collagen. The COL3A1 gene produces the components of type III collagen, called pro-alpha1(III) chains. Three copies of this chain combine to make a molecule of type III procollagen. These triple-stranded, rope-like procollagen molecules must be processed by enzymes outside the cell to remove extra protein segments from their ends. Once these molecules are processed, the collagen molecules arrange themselves into long, thin fibrils. Within these fibrils, the individual collagen molecules are cross-linked to one another. These cross-links result in the formation of very strong mature type III collagen fibrils, which are found in the spaces around cells.

Glycoprotein VI (GPVI) is a 63 kDa platelet megakaryocyte-specific type I transmembrane glycoprotein of the immunoglobulin superfamily that is an important collagen receptor and initiator of platelet activation, aggregation and thrombin generation. GPVI is also a secondary receptor required for platelet spreading on laminin. GPVI associates with the Fc receptor gamma -chain via charged aa in the TM domains of GPVI (arginine) and the FcR gamma (aspartic acid). Collagen binding by the GPVI Ig-like domains initiates signaling through the FcR gamma ITAM sequence. Dimerization of GPVI (2:2 with FcR gamma ) and N-glycosylation greatly enhances collagen binding. Type I and III collagens are strong thrombus-forming components in the vascular subendothelium and atherosclerotic plaques. GPVI initiates binding to fibrillar collagens under flow conditions, then activates integrin alpha 2 beta 1 which binds collagen more tightly. GPVI deficiencies cause only a mild bleeding tendency, probably because integrin alpha 2 beta 1 is able to minimally initiate collagen binding. Normal human GPVI concentration can vary widely and affect maximum thrombin generation. Engagement of GPVI by collagens or other agonists, including autoantibodies, causes calmodulin-regulated metalloproteinase cleavage of the 57 kDa ECD and depletes surface GPVI.