The fibril structure of type V collagen triple-helical domain

Abstract

Although the triple-helical structure of fibrillar collagen is regarded in general as being quite similar, each type of collagen molecule has inherent characteristics in the triple-helical domain. Few studies have ever been performed in terms of the aggregate structure of the triple-helical domain of fibrillar collagen. Reconstituted aggregates from the purified triple-helical domain of each type of fibrillar collagen might amplify the subtle differences in the structural characteristics of each type of collagen molecule. In this study, the reconstituted aggregate structure of pepsin-treated type V collagen (type Vp collagen), that is, virtually its triple-helical domain was characterized by transmission electron microscopy. Pepsin-treated type I (type Ip) and type II (type IIp) collagen were compared with type Vp collagen. Unique features of the aggregate structure of the triple-helical domain of the type V collagen can be summarized as follows:1.Type Vp collagen formed fibrils with the D-periodic banding pattern. The banded type Vp fibrils appeared to be of a loosely twisted ribbon-like structure. The average thickness of type Vp collagen fibrils with the banding pattern was significantly smaller than those reconstituted from types Ip and IIp collagen.2.The width of the type Vp collagen fibrils was not affected under the conditions where the D-periodic banded fibrils were formed; the conditions being incubation temperature, protein concentration, and NaCl concentration.3.Type Vp collagen fibrils had little branching and merging. Furthermore, the type Vp collagen fibrils did not bind to each other. On the contrary, type Ip collagen fibrils were often bound to each other and had many branching and merging.These results suggested that the lateral packing of the triple-helical domain of type V collagen is determined by its molecular structure. The characteristics of type Vp collagen fibrils might be explained by their characteristic amino acid composition. A significant feature of the triple-helical domain of type V collagen is the high content of glycosylated hydroxylysine residues. Molecular model building of the collagenous structure suggests that a change in surface roughness is conspicuous by incorporating the glycosylated hydroxylysine residues. More than a ten-fold content of bulky glycosylated hydroxylysine residues in type V collagen compared to that of type I might have a significant influence on both the intermolecular and interfibrillar interactions of the triple-helical domain of type V collagen molecule.