RECOMBINANT EXPRESSION AND STRUCTURAL AND BINDING-PROPERTIES OF ALPHA-1(VI) AND ALPHA-2(VI) CHAINS OF HUMAN COLLAGEN TYPE-VI

Full-length alpha 1(VI) and alpha 2(VI) cDNAs in an eukaryotic express ion vector were used to obtain stably transfected human kidney cell cl ones and to purify these collagen-VI chains in substantial quantities from the culture medium. Both chains appeared mainly as monomers toget her with some dimers that were disulfide linked through their C-termin al globular domains. Despite sufficient hydroxylation of proline and l ysine residues, the chains did not form a triple-helix, as shown by el ectronmicroscopy, CD spectra and pepsin sensitivity. Digestion of the chains with bacterial collagenase released the N-terminal and C-termin al globular domains, which were identified by their size and partial s equences. They showed a substantial content of a-helical conformation and a distinct globular structure after rotary shadowing. Antibodies c ould be raised that distinguished between the two chains and reacted w ith the globular domains. The alpha 2(VI) but not the alpha 1(VI) chai n showed binding to a heparan sulfate proteoglycan (perlecan), fibrone ctin and pepsin-solubilized collagen VI. Purified globular domains did not bind these ligands indicating the localization of binding sites w ithin the triple-helical domain. Both chains showed a distinct affinit y for heparin but failed to bind to various collagen types.