THE ALPHA-1(VIII) AND ALPHA-2(VIII) CHAINS OF TYPE-VIII COLLAGEN CAN FORM STABLE HOMOTRIMERIC MOLECULES

Type VIII collagen is a short chain collagen. Two chains have been des cribed, alpha 1(VIII) and alpha 2(VIII), but the chain composition of type VIII collagen is far from resolved. To address this question, we have expressed full-length alpha 1(VIII) and alpha 2(VIII) chains in a n in vitro translation system supplemented with semipermeabilized cell s. Both chains gave a translation product of similar to 80 kDa that co uld be shown to produce a chymotrypsin/trypsin-resistant product of si milar to 60 kDa, indicating that both chains could form homotrimers. H ydroxylation of proline residues was a prerequisite for stable trimer formation. The melting temperature for the alpha 1(VIII) homotrimer wa s 45 degrees C, whereas that for alpha 2(VIII) was 42 degrees C. The a bility of both chains of type VIII collagen to form stable triple heli ces suggests that there may be different forms of this collagen and th at cells may modulate the chain composition in response to different b iological conditions.