Chemical cross-linking restrictions on models for the molecular organization of the collagen fibre

Abstract

The nature of the precise packing of collagen molecules into a collagen fibril, producing the characteristic regular banding, is still debatable. The problem has been approached using electron microscopy and X-ray diffraction techniques, and several models have been proposed, including hexagonal packing, an octafibril structure, a two-strand rope and a five-strand rope (for review, see ref. 1). For the past decade the pentafibrillar model, originally proposed by Smith², has been widely accepted as the fundamental building unit. This model, based on the quarter-stagger end-overlap hypothesis of Hodge and Petruska³, was supported by the X-ray diffraction data of Miller and Wray⁴. These X-ray data have now been reinterpreted by Huhnes and Miller⁵ in terms of a quasi-hexagonal packing of collagen molecules. We argue here that until other characteristic parameters are taken into account, in particular the chemical cross-linking evidence, the packing problem is still unresolved.