Molecular Basis for Fibrillar Aggregation of Tropocollagen

Abstract

NO model for the three dimensional packing of tropocollagen (TC) molecules into fibrils^1–3 approaches the problem on a molecular level; such analysis requires the assumption of a specific macromolecular structure^4–6 and of a specific aggregation state^7,8 of TC molecules. If the Ramachandran, Rich and Crick structure with the a1 chains in register from the N-terminus and the quarter stagger mode of association are assumed, then corresponding residues in the a chains will be separated by 108° radial angles^4,6. Possible intermolecular associations, producing quarter-staggered⁷ TC aggregation, fall into two general classes: (1) association involving a single chain in one molecule with a single chain in another and (2) complex association loci involving more than one chain in each TC molecule. The former is the more likely possibility and would involve residues on an individual a chain, at intervals governed by the pitch of the super helix, forming a longitudinal edge which associates in a defined plane of contact with a complementary edge in a neighbouring TC molecule^2,4,6.