title: Type-III procollagen assembly in semi-intact cells: chain association, nucleation and triple-helix folding do not require formation of inter-chain disulphide bonds but triple-helix nucleation does require hydroxylation.
abstract: Procollagen assembly is initiated within the endoplasmic reticulum by three alpha-chains associating via their C-propeptides (C-terminal propeptides). To study the requirements for the association of procollagen monomers at synthesis we have reconstituted the initial stages in the folding, assembly and modification of procollagen using semi-permeabilized cells. By translating a type-III procollagen "mini-gene' which lacks part of the triple-helical domain, we demonstrate that these cells efficiently carry out the assembly of hydroxylated, triple-helical, procollagen trimers and allow the identification of specific disulphide-bonded intermediates in the folding pathway. Mutant chains, which lack the ability to form inter-chain disulphide bonds within the C-propeptide, were still able to assemble within this system. Furthermore, characterization of the trimeric molecules formed suggested that inter-chain disulphide bonds had formed within the C-telopeptide (C-terminal telopeptide). However, when hydroxylation of prolyl and lysyl residues was inhibited no inter-chain disulphide bonds were formed in the C-telopeptide, indicating that hydroxylation is required for the initial nucleation of the triple-helical domain. Mutant chains which lacked the ability to form inter-chain disulphide bonds within the C-propeptide or the C-telopeptide could still assemble to form trimeric triple-helical molecules linked by inter-chain disulphide bonds within the N-propeptide (N-terminal propeptide). These results indicate that inter-chain disulphide bond formation within the C-propeptide or the C-telopeptide is not required for chain association and triple-helix formation.
authors.affiliation: School of Biological Sciences, University of Manchester, U.K.
authors.forename: N J
authors.initials: NJ
authors.lastname: Bulleid
authors.forename: R
authors.initials: R
authors.lastname: Wilson
authors.forename: J F
authors.initials: JF
authors.lastname: Lees
mesh_terms: D000595:Amino Acid Sequence; D002463:Cell Membrane Permeability; D003545:Cysteine / Q000235:genetics; D004220:Disulfides / Q000378:metabolism; D006900:Hydroxylation; D008969:Molecular Sequence Data; D009154:Mutation; D011347:Procollagen / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D004220:Disulfides; D011347:Procollagen; D011994:Recombinant Proteins; D003545:Cysteine