The α1(VIII) and α2(VIII) chains of type VIII collagen can form stable homotrimeric molecules

Abstract

Type VIII collagen is a short chain collagen. Two chains have been described, α1(VIII) and α2(VIII), but the chain composition of type VIII collagen is far from resolved. To address this question, we have expressed full-length α1(VIII) and α2(VIII) chains in an in vitro translation system supplemented with semipermeabilized cells. Both chains gave a translation product of ~80 kDa that could be shown to produce a chymotrypsin/trypsin- resistant product of ~60 kDa, indicating that both chains could form homotrimers. Hydroxylation of proline residues was a prerequisite for stable trimer formation. The melting temperature for the α1 (VIII) homotrimer was 45°C, whereas that for α2(VIII) was 42°C. The ability of both chains of type VIII collagen to form stable triple helices suggests that there may be different forms of this collagen and that cells may modulate the chain composition in response to different biological conditions.