Recombinant Mouse GPVI Protein, CF

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 thrombus generation (1, 2). GPVI is also a secondary receptor required for platelet spreading on laminin (3). Mouse GPVI contains a 21 amino acid (aa) signal sequence, a 244 aa extracellular domain (ECD) that has two C‑type Ig‑like domains followed by a mucin‑like, presumably O‑glycosylated Ser‑Thr‑rich region, a 21 aa transmembrane (TM) domain and a 27 aa cytoplasmic tail. Mouse GPVI ECD shares 70%, 85%, 69% and 66% aa identity with human, rat, equine and canine GPVI ECD, respectively. A 296 aa mouse isoform lacking aa 224 ‑ 240 has been described (4). GPVI associates with the Fc receptor gamma‑chain via charged aa in the TM domains of GPVI (arginine) and the FcR gamma (aspartic acid) (2). Collagen binding by the GPVI Ig‑like domains initiates signaling through the FcR gamma ITAM sequence (2). Dimerization of GPVI (2 CPVI monomers: FcR gamma dimer) and N‑glycosylation greatly enhances collagen binding (5, 6). Type I and III collagens are strong thrombus‑forming components in the vascular subendothelium and atherosclerotic plaques (7). GPVI initiates binding to fibrillar collagens under flow conditions, then activates integrin alpha₂ beta₁ which binds collagen more tightly (8). GPVI deficiencies cause only a mild bleeding tendency, in part because integrin alpha₂ beta₁ is able to minimally initiate collagen binding (8). Engagement of GPVI by collagens or other agonists, including GPVI antibodies, causes cleavage of the 57 kDa ECD by ADAM10, TACE/ADAM17, or other proteases, depleting surface GPVI (9, 10). In rheumatoid arthritis, collagen engagement of synovial platelet GPVI produces platelet microparticles that contribute to inflammation (11).