Type VIII collagen: heterotrimeric chain association

Two chains, alpha1(VIII) and alpha2(VIII), have been described for type VII I collagen. Early work suggested that these chains were present in a 2:1 ra tio, although recent work has shown that homotrimers can form and predomina te in some tissues. In order to address the question of whether the alpha1( VIII) and alpha2(VIII) chains could co-polymerise we made a shortened alpha 1(VIII) chain and expressed this with full length alpha2(VIII) chain in an in vitro translation system supplemented with semi-permeabilised cells. Het erotrimers containing either two or one alpha2(VIII) were evident. Interest ingly, a point mutation in the NCl domain of the alpha1(VIII) chain abrogat ed trimer formation. In addition we were able to demonstrate chain associat ion of the alpha1(X) chain of type X collagen with the shortened alpha1(VII I) chain. Variations in chain association were seen when altered ratios of message were used. These results demonstrate the importance of the NCl doma in in chain association and suggest that gene expression regulates the comp osition and function of type VIII collagen by varying chain composition. (C ) 2001 Elsevier Science Ltd. All rights reserved.