title: Trimerization of collagen IX alpha-chains does not require the presence of the COL1 and NC1 domains.
abstract: Collagen IX is a heterotrimer of three alpha-chains, which consists of three COL domains (collagenous domains) (COL1-COL3) and four NC domains (non-collagenous domains) (NC1-NC4), numbered from the C-terminus. Although collagen IX chains have been shown to associate via their C-terminal NC1 domains and form a triple helix starting from the COL1 domain, it is not known whether chain association can occur at other sites and whether other collagenous and non-collagenous regions are involved. To address this question, we prepared five constructs, two long variants (beginning at the NC4 domain) and three short variants (beginning at the COL2 domain), all ending at the NC2 domain (or NC2 replaced by NC1), to study association and selection of collagen IX alpha-chains. Both long variants were able to associate with NC1 or NC2 at the C-terminus and form various disulfide-bonded trimers, but the specificity of chain selection was diminished compared with full-length chains. Trimers of the long variant ending at NC2 were shown to be triple helical by CD. Short variants were not able to assemble into disulfide-bonded trimers even in the presence of both conserved cysteine residues from the COL1-NC1 junction. Our results demonstrate that collagen IX alpha-chains can associate in the absence of COL1 and NC1 domains to form a triple helix, but the COL2-NC2 region alone is not sufficient for trimerization. The results suggest that folding of collagen IX is a co-operative process involving multiple COL and NC domains and that the COL1-NC1 region is important for chain specificity.
authors: Collagen Research Unit, Biocenter and Department of Medical Biochemistry and Molecular Biology, Oulu University, P.O. Box 5000, 90014 Oulu, Finland.
authors: Juha
authors: J
authors: Jäälinoja
authors: Joni
authors: J
authors: Ylöstalo
authors: William
authors: W
authors: Beckett
authors: David J S
authors: DJ
authors: Hulmes
authors: Leena
authors: L
authors: Ala-Kokko
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D024081:Collagen Type IX / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D024081:Collagen Type IX; D011994:Recombinant Proteins