Structural analysis of collagen fibrils in rat skin based on small-angle X-ray-diffraction pattern

A superhelix structure is proposed to explain the short band period (65 nm) observed in rat skin collagen fibrils in comparison with that of tendon collagen fibrils (67 nm). In the former case, each molecule forms an angle of 12-13 degrees with the fibril axis and almost ten tropocollagen molecules aggregate to form a tilting plane in a bundle or a subfibril. The adjacent bundles may be staggered with respect to each other by a length of ten amino acid residues along the chain axis to form the band structure observed to be normal to the fibril axis. This model is found to be quantitatively consistent with small-angle X-ray diffraction data obtained from uniaxially oriented collagen fibrils in native rat skin as well as a transmission electron microscopic image of freeze-etched fibrils in glycerinated rat skin.