Aggregation of a type I collagen precursor containing N-terminal propeptides

Aggregation properties of type I pNcollagen from dermatosparactic sheep skin were studied by electron microscopy and turbidity measurements. pNcollagen was less soluble than collagen at low temperatures. Upon heating to 37 degrees C, it polymerized into thin, flat fibrils showing the same periodicity as collagen but with a less distinct gap-overlap pattern. The apparent critical concentration was 0.01-0.03 mg/ml at temperatures between 32-37 degrees C and was higher than that for collagen under similar conditions. The total turbidity change with heat polymerization of the pNcollagen was less than with heat polymerization of collagen under the same conditions. Also, the total change in turbidity showed a different temperature dependence and the kinetics of the reaction were slower than with collagen. However, the effects of protein concentration, ionic strength and pH on the rate of polymerization of pNcollagen were similar to those observed with collagen. The kinetics of polymerization of pNcollagen were explained by a model based on nucleation and growth processes which permits end-to-end association of fibrils, but only limited lateral association because of the presence of the N-terminal propeptides.