Type VIII collagen: Heterotrimeric chain association

Two chains, α1(VIII) and α2(VIII), have been described for type VIII collagen. Early work suggested that these chains were present in a 2:1 ratio, although recent work has shown that homotrimers can form and predominate in some tissues. In order to address the question of whether the α1(VIII) and α2(VIII) chains could co-polymerise we made a shortened α1(VIII) chain and expressed this with full length α2(VIII) chain in an in vitro translation system supplemented with semi-permeabilised cells. Heterotrimers containing either two or one α2(VIII) were evident. Interestingly, a point mutation in the NC1 domain of the α1(VIII) chain abrogated trimer formation. In addition we were able to demonstrate chain association of the α1(X) chain of type X collagen with the shortened α1(VIII) chain. Variations in chain association were seen when altered ratios of message were used. These results demonstrate the importance of the NC1 domain in chain association and suggest that gene expression regulates the composition and function of type VIII collagen by varying chain composition. © 2001 Elsevier Science Ltd.