Noncollagenous region of the streptococcal collagen-like protein is a trimerization domain that supports refolding of adjacent homologous and heterologous collagenous domains.

Proper folding of the (Gly-Xaa-Yaa)(n) sequence of animal collagens requires adjacent N- or C-terminal noncollagenous trimerization domains which often contain coiled-coil or beta sheet structure. Collagen-like proteins have been found recently in a number of bacteria, but little is known about their folding mechanism. The Scl2 collagen-like protein from Streptococcus pyogenes has an N-terminal globular domain, designated V(sp), adjacent to its triple-helix domain. The V(sp) domain is required for proper refolding of the Scl2 protein in vitro. Here, recombinant V(sp) domain alone is shown to form trimers with a significant alpha-helix content and to have a thermal stability of T(m) = 45 degrees C. Examination of a new construct shows that the V(sp) domain facilitates efficient in vitro refolding only when it is located N-terminal to the triple-helix domain but not when C-terminal to the triple-helix domain. Fusion of the V(sp) domain N-terminal to a heterologous (Gly-Xaa-Yaa)(n) sequence from Clostridium perfringens led to correct folding and refolding of this triple-helix, which was unable to fold into a triple-helical, soluble protein on its own. These results suggest that placement of a functional trimerization module adjacent to a heterologous Gly-Xaa-Yaa repeating sequence can lead to proper folding in some cases but also shows specificity in the relative location of the trimerization and triple-helix domains. This information about their modular nature can be used in the production of novel types of bacterial collagen for biomaterial applications.