Amino acid sequence of the N-terminal non-triple helical cross link region of type III collagen

Abstract

The structural integrity of the collagen fibril and possibly the catabolism of the collagen molecule is determined to a large extent by the type and density of collagen intermolecular cross links. The major intermolecular cross links in type I collagen are those derived from lysine residues [ 1 ] . There are two structural requirements necessary for the formation of this type of cross link. First, the presence of a lysine or hydroxylysine residue in the N and/or C non-triple helical regions of collagen which have been enzymatically converted to an aldehyde form. Second, a lysine or hydroxylysine residue present in the triple helical region of the molecule in a position such that it aligns with the above described aldehyde when the molecules are in a quarter staggered arrangement as found in collagen fibrils [2]. The discovery of type III collagen presented, for the first time, a situation in which two types of collagen (types I and III), exhibiting different macromolecular organisations, are found in close association in the same tissue [3]. It has been established that, unlike type I, type III collagen contains cysteine residues which form interchain disulphide cross links [4]. Type III collagen in adult tissues is insoluble, but can be extracted from pepsin solubilised material. As the cysteine cross links are still present in pepsin solubilised type III collagen, this indicates that, like