Recombinant expression and structural and binding properties of α1(VI) and α2(VI) chains of human collagen type VI

Full‐length α1(VI) and α2(VI) cDNAs in an eukaryotic expression vector were used to obtain stably transfected human kidney cell clones and to purify these collagen‐VI chains in substantial quantities from the culture medium. Both chains appeared mainly as monomers together with some dimers that were disulfide linked through their C‐terminal globular domains. Despite sufficient hydroxylation of proline and lysine residues, the chains did not form a triple‐helix, as shown by electronmicroscopy, CD spectra and pepsin sensitivity. Digestion of the chains with bacterial collagenase released the N‐terminal and C‐terminal globular domains, which were identified by their size and partial sequences. They showed a substantial content of α‐helical conformation and a distinct globular structure after rotary shadowing. Antibodies could be raised that distinguished between the two chains and reacted with the globular domains. The α2(VI) but not the α1(VI) chain showed binding to a heparan sulfate proteoglycan (perlecan), fibronectin and pepsin‐solubilized collagen VI. Purified globular domains did not bind these ligands indicating the localization of binding sites within the triple‐helical domain. Both chains showed a distinct affinity for heparin but failed to bind to various collagen types.