Macromolecular component of the subendothelium. Major component of the Descemet's membrane (basement membrane) of corneal endothelial cells. Also a component of the endothelia of blood vessels. Necessary for migration and proliferation of vascular smooth muscle cells and thus, has a potential role in the maintenance of vessel wall integrity and structure, in particular in atherogenesis (By similarity). Vastatin, the C-terminal fragment comprising the NC1 domain, inhibits aortic endothelial cell proliferation and causes cell apoptosis. Homotrimers, or heterotrimers in association with alpha 2(VIII) type collagens. Four homotrimers can form a tetrahedron stabilized by central interacting C-terminal NC1 trimers (By similarity). Prolines at the third position of the tripeptide repeating unit (G-X-Y) are hydroxylated in some or all of the chains. Proteolytically cleaved by neutrophil elastase, in vitro. Proteolytic processing produces the C-terminal NC1 domain fragment, vastatin (By similarity). 4 consecutive G-P-P tripeptides are present at the C-terminus of the triple-helical region. These may provide high thermal stability of this region.