Multimerin is a massive, disulfide-linked protein with a unique complementary DNA sequence. It is stored in platelets and the endothelium of blood vessels and is comprised of subunits linked by interchain disulfide bonds to form large, variably sized homomultimers. The multimerin subunits are derived from a common precursor protein, promultimerin, which undergoes proteolysis and extensive N-glycosylation during biosynthesis. The complementary DNA sequence of multimerin indicates that multimerin is a novel protein, with Arg-Gly-Asp-Ser, coiled-coil, and epidermal growth factor-like domains. The C-terminal region of multimerin resembles the globular head domain of complement C1q and collagens type VIII and X. Multimerin is expressed by megakaryocytes and endothelial cells and stored within platelet alpha granules and endothelial cell Weibel-Palade bodies. Following cellular activation, multimerin is released and binds to these cells and the extracellular matrix. The function of this novel protein in hemostasis is under investigation. Recent studies have identified multimerin as a specific Factor V/Va binding protein that is complexed with Factor V within platelet alpha granules.
