GLY-GLY-CONTAINING TRIPLETS OF LOW STABILITY ADJACENT TO A TYPE-III COLLAGEN EPITOPE

Collagens, in addition to their structural role in the extracellular m atrix, possess a number of functional binding domains. In this study, the binding to collagen of a monoclonal antibody is used as a model to define the molecular features involved in triple-helix interactions w ith other proteins. Here we report the thermal stability of an overlap ping set of triple-helical peptides that includes the epitope recogniz ed by a monoclonal antibody to type LII collagen. Although the sequenc es of these peptides are very closely related, by a translation of a s ingle triplet along the collagen chain, substantial variations in the melting temperatures were observed. These variations in thermal stabil ity could not be readily explained by differences in imino acid conten t, or in numbers of charged or hydrophobic residues. The results indic ate that Gly-Gly-Y triplets, which are adjacent to the epitope, have a strong influence in reducing the thermal stability of triple-helical peptides. Further studies, which were carried out on a set of ''host-g uest'' triple-helical peptides containing different Gly-Gly-Y guest tr iplets, confirm the destabilizing effect of such tripeptides. The pres ence of Gly-Gly-Y triplets may play an important role in specific func tions of type III collagen by modulating the local triple-helical stru cture or dynamics.