Recombinant alpha 1(VIII) collagen chains form homotrimers in vitro

Type VIII collagen, a member of the short chain collagen family, is expressed in large blood vessels and in the subendothelium and mesangium of the glomerulus. While two genetically distinct type VIII collagen chains, alpha 1 and alpha 2, have been identified, it is not known whether type VIII collagen exists as homotrimers or heterotrimers. To determine whether alpha 1(VIII) collagen chains can associate to form homotrimers, a full length human alpha 1(VIII) collagen cDNA was generated by overlap extension PCR and used as a substrate for coupled in vitro transcription/translation. A translation product of 80kDa, the predicted size of alpha 1(VIII) collagen, was identified by autoradiography of SDS-gels containing radiolabelled translation products. Sensitivity of the in vitro translated protein to digestion with bacterial collagenase and trypsin and the size of the proteins generated by these digestions provide evidence that alpha 1(VIII) collagen can participate in the formation of homotrimers.