The noncollagenous domain 1 of type X collagen. A novel motif for trimer and higher order multimer formation without a triple helix.

In this study, we test the hypothesis that the carboxyl noncollagenous (NC1) domain of collagen X is sufficient to direct multimer formation without a triple helix. Two peptides containing the NC1 domain of avian collagen X have been synthesized using a bacterial expression system and their properties characterized. One peptide consists only of the NC1 domain, and the other is a chimeric molecule with a noncollagenous A domain of matrilin-1 fused to the N terminus of NC1. The NC1 peptide alone forms a 45-kDa trimer under native conditions, suggesting that NC1 contains all the information for trimerization without any triple helical residues. This trimeric association is highly thermostable without intermolecular disulfide bonds. This indicates that the NC1 domain contributes to the remarkable structural stability of collagen X. Chemical cross-linking of the NC1 trimer results in a series of varying sized multimers, the smallest of which is a trimer. Therefore the NC1 trimer is sufficient to form higher order multimers. The chimeric A-NC1 peptide forms a homotrimer by itself, and a series of heterotrimers with the NC1 peptide via the NC1 domain. Thus the NC1(X) domain directs multimer formation, even in a noncollagenous molecule.