[New collagenous proteins: FACIT collagens, transmembrane collagens and multiplexins]

Collagens are the main components of the extracellular matrix and they constitute about 30% of total body protein. Each collagen molecule consists of three polypeptide chains that intertwine in one or more places into triple helical domains, a very rare structure in other proteins. Nineteen collagen types have been described to date and these forming banded fibrils are the most abundant. In the last decade new collagenous proteins were discovered that have been classified into three distinct groups: fibril-associated collagens with interrupted triple helices (FACITs), transmembrane collagens and multiplexins. FACITs appear to connect collagen fibrils to other matrix components or cells. Transmembrane collagens have intracellular domains and they participate in cell adhesion and probably in signal transduction. Multiplexins are situated mainly in basement membranes and contain sequences, which demonstrate features of angiogenesis inhibitors reducing the growth of neoplasmatic tumours.