A comparison of models for the macromolecular structure of interstitial and basement membrane collagens

Despite the large quantity of data available concerning the structure of the collagen molecule, the way in which molecules aggregate to fibrils and how they are stabilized by crosslinks is still not clearly understood. At present, two models, based mainly on X-ray and electron microscopic data, are being discussed. Until recently, chemical evidence to support either one of these models was lacking. The isolation and partial characterization of trifunctional crosslinked peptides has helped to define the spatial relationships of the collagen molecules within a fibril. Basement membrane collagen, although possessing many characteristics of interstitial collagens, does not appear to form fibrils. The molecules are crosslinked into a three-dimensional network and although this bears no resemblance to the fibrils of interstitial collagens, structural studies have revealed that the same constructional principles are probably involved, indicating a common genetic ancestor for these molecules. In this presentation the two most favoured models for the macromolecular structure of the interstitial collagens are described and compared and contrasted with a model for basement membrane collagen. Some of the more recent data on collagen crosslinks is discussed in connection with these models.