Helical model of nucleation and propagation to account for the growth of type I collagen fibrils from symmetrical pointed tips: a special example of self-assembly of rod-like monomers.

A model was developed to account for the recent observations indicating that type I collagen fibrils assembled in vivo grow from symmetrical pointed tips. The essential features of the model are (i) a distinctive structural nucleus forms at each end of a growing fibril and growth of the fibril then proceeds by propagation of the two structural nuclei, (ii) the two structural nuclei have similar spiral or helical conformations, and (iii) assembly of each structural nucleus requires two kinds of specific binding steps defined as 3.4 D-period and 0.4 D-period overlaps, but propagation of the nucleus requires only the 3.4 D-period binding step.