Interaction of tropocollagen with protein-polysaccharide complexes. An analysis of the ionic groups responsible for interaction

Human intervertebral disc protein-polysaccharide complex (PP-L) has been separated by isoelectric focussing analysis into three main subunits and four minor components. PP-L interacted with tropocollagen in the isoelectric-focussing column to yield a single complex zone, containing both uronic acid and hydroxyproline, with an isoionic point intermediate between those of tropocollagen and PP-L. This complex, formed at 4°, was shown by electron microscopy to be in the form of fibrous long-spacing fibrils, whilst the complex formed at 37° consisted of native-type fibrils. Chemical and enzymic modification of the PP-L demonstrated that the sulphate group was largely responsible for interaction with tropocollagen during isoelectric focussing. The initial interaction was independent of the core protein and independent of the length of the glycosaminoglycan chains. The guanidino groups of arginine and the ε{lunate}-amino groups of lysine were found to be the sites of interaction of tropocollagen with PP-L.