The quaternary and fibrillar structure of native collagen

Abstract

A theoretical discussion of the quaternary and fibrillar structure of the native collagen molecule is based on a macromolecular micelle model. The macromolecular micelle is a macromolecular chain wound into a spiral which consists of straight lengths of chains and curves, the general form being in the solid state a planar ovoid disk which is able to swell in solution. The micelle is characterized by the length, L₀, of the first straight link (before the first curve), by the overall length, H, and width, h, of the micelle. From viscosity measurements $\text{L}{}_0\text{= 85 ± 10}\text{A}\text{̊}$. In a native collagen filament or fibre, the micelles are aligned side by side in such a way that the axis H is parallel to the axis of the fibre or filament, and that the overall length of the micelle corresponds to the periodic values obtained by electron microscope studies of the native fibre or filament. Furthermore the typical geometrical features of the native fibres and filaments can be easily explained by the model. Assuming that the rod-like structure of tropocollagen is the result of an unfolding of the macromolecular micelle, it is possible to find a good relationship between the band patterns observed on SLS-fibrils and native type filaments. The theoretical model built for the tropocollagen micelle shows the existence of at least four bands which may correspond to the a₂-, a₃-, b₁- and b₂-bands discussed by Grassmann. The rod-like structure of tropocollagen is considered to be a special denaturated form of collagen uniquely obtained under certain conditions of temperature.