IDENTIFICATION OF THE MOLECULAR RECOGNITION SEQUENCE WHICH DETERMINESTHE TYPE-SPECIFIC ASSEMBLY OF PROCOLLAGEN

A key question relating to procollagen biosynthesis is the way in whic h closely related procollagen chains discriminate between each other t o assemble in a type-specific manner, Intracellular assembly of procol lagen occurs via an initial interaction between the C-propeptides foll owed by vectorial propagation of the triple-helical domain in the C to N direction. Recognition signals within the C-propeptides must, there fore, determine the selective association of individual procollagen ch ains. We have used the pro alpha 1 chain of type III procollagen [pro alpha 1(III)] and the pro alpha 2 chain of type I procollagen [pro alp ha 2(I)] as examples of procollagen chains that are either capable or incapable of self-assembly. When we exchanged the C-propeptides of the pro alpha 1(III) chain and the pro alpha(I) chain we demonstrated tha t 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 c onstructed a series of chimeric procollagen chains in which we exchang ed specific sequences from the pro alpha 1(III) C-propeptide with the corresponding region within the pro alpha 2(I) C-propeptide (and vice versa) and assayed for the ability of these molecules to form homotrim ers. Using this approach we have identified a discontinuous sequence o f 15 amino acids which directs procollagen self-association. By exchan ging this sequence between different procollagen chains we can direct chain association and, potentially, assemble molecules with defined ch ain compositions.