The synthetic polytripeptides (Pro-Pro-Gly) 10 and (Pro-Pro-Gly) 20 form micro-crystalline structures similar to segmental structures formed by collagen

Abstract

Previous studies demonstrated that (Pro-Pro-Gly) 10 and (Pro-Pro-Gly) 20 prepared by a specific modification of the Merrifield technique form triple-helical structures in aqueous solution similar to tropocollagen. In the present studies we used electron microscopy to demonstrate that at about 4 °C the same polytripeptides also form larger structures which we consider to be micro-crystalline segments. Examination of the micro-crystalline segments by negative staining with sodium silicotungstate demonstrated that one lateral dimension was relatively constant and was approximately equal to the theoretical length of the polytripeptides in a collagen-like triple helix. Also, when (Pro-Pro-Gly) 20 was negatively stained with uranyl acetate, smaller structures were seen which were of the same length as the “regular dimension” of the micro-crystalline segments and which probably were individual triple helices. Selective positive staining of either the amino-terminal or the carboxy-terminal groups indicated that the ends of the polytripeptide chains were packed in an anti-parallel fashion within the segments. The results obtained by both negative and positive staining are best explained by a scheme in which (a) the polytripeptide chains within triple helices are in register and parallel, and (b) the micro-crystalline segments are formed by the lateral aggregation of triple helices in an anti-parallel fashion.