ABSTRACT
Hsp47 is a heat-shock protein that interacts transiently with procollagen during its folding, assembly and transport from the endoplasmic reticulum (ER) of mammalian cells. It has been suggested to carry out a diverse range of functions, such as acting as a molecular chaperone facilitating the folding and assembly of procollagen molecules, retaining unfolded molecules within the ER, and assisting the transport of correctly folded molecules from the ER to the Golgi apparatus. Here we define the substrate recognition of Hsp47, demonstrating that it interacts preferentially with triple-helical procollagen molecules. The association of Hsp47 with procollagen coincides with the formation of a collagen triple helix. This demonstrates that Hsp47's role in procollagen folding and assembly is distinct from that of prolyl 4-hydroxylase. These results indicate that Hsp47 acts as a novel molecular chaperone, potentially stabilizing the correctly folded collagen helix from heat denaturation before its transport from the ER.
Subject(s)
Heat-Shock Proteins/chemistry , Procollagen/chemistry , Protein Folding , Animals , Heat-Shock Proteins/metabolism , Molecular Chaperones/chemistry , Molecular Chaperones/metabolism , Procollagen/metabolism , Protein Binding , Rabbits , Recombinant Proteins/chemistry , Recombinant Proteins/metabolismABSTRACT
A key question relating to procollagen biosynthesis is the way in which closely related procollagen chains discriminate between each other to assemble in a type-specific manner. Intracellular assembly of procollagen occurs via an initial interaction between the C-propeptides followed by vectorial propagation of the triple-helical domain in the C to N direction. Recognition signals within the C-propeptides must, therefore, determine the selective association of individual procollagen chains. We have used the pro alpha1 chain of type III procollagen [pro alpha1(III)] and the pro alpha2 chain of type I procollagen [pro alpha2(I)] as examples of procollagen chains that are either capable or incapable of self-assembly. When we exchanged the C-propeptides of the pro alpha1(III) chain and the pro alpha(I) chain we demonstrated that this domain is both necessary and sufficient to direct the assembly of homotrimers with correctly aligned triple-helices. To identify the sequences within this domain that determine selective association we constructed a series of chimeric procollagen chains in which we exchanged specific sequences from the pro alpha1(III) C-propeptide with the corresponding region within the pro alpha2(I) C-propeptide (and vice versa) and assayed for the ability of these molecules to form homotrimers. Using this approach we have identified a discontinuous sequence of 15 amino acids which directs procollagen self-association. By exchanging this sequence between different procollagen chains we can direct chain association and, potentially, assemble molecules with defined chain compositions.
Subject(s)
Procollagen/biosynthesis , Amino Acid Sequence , Collagenases/metabolism , Disulfides/chemistry , Electrophoresis, Polyacrylamide Gel , Molecular Sequence Data , Mutagenesis, Site-Directed , Mutation , Procollagen/chemistry , Procollagen/genetics , Protein Conformation , Protein Folding , Recombinant Proteins/biosynthesis , Sequence AlignmentABSTRACT
The rat neuronal nitric oxide synthase (nNOS) cDNA was expressed in Saccharomyces cerevisiae under the control of a hybrid PGK/GAL promoter, PAL. Galactose induction resulted in the production of a soluble 160 kDa protein that was recognised by anti-neuronal NOS antibody. NOS activity was detected by the conversion of [3H]arginine to [3H]citrulline and required the addition of the cofactors, calmodulin and tetrahydrobiopterin. The activity was inhibited by the arginine analogues NG-nitro-L-arginine and NG-nitro-L-arginine methyl ester.
