A discussion on the structure of proteins - Introduction

Abstract

It has long been known from X-ray and supporting studies of the fibrous proteins that they are mainly of two configurational types related to their extensibility and elastic properties (see, for example, Astbury 1940, 1947 a ). In the first (the k. -m. -e. -f. group), comprising mammalian keratin, myosin, epidermin, fibrinogen, etc., the polypeptide chains are normally in a regularly folded state ( α -form), from which they can be extended into the almost straight β -form or ‘supercontracted’ into some still shorter configuration. And belonging to this same family is a subgroup represented by the keratin of feathers, beaks, claws, shells, scales, etc., of birds and reptiles, in which the chains are in a β -configuration naturally, though one that is about 7% shorter than that of mammalian β -keratin. In the second great family (the collagen group), which includes tendons, white connective tissue, cartilage, elastoidin, and so on, the polypeptide chains are normally in a con­figuration which is apparently extended (and not further extensible) but is quite distinct from the β -form of the k. -m. -e. -f. group; though they are again strongly contractile under the right conditions, shortening under the influence of tem­perature and swelling to less than a quarter of their ordinary length. It has also long been known from the same series of investigations that similar concepts must hold for the corpuscular proteins; in general, they too are systems of folded chains—systems that become disorganized on denaturation and can then be drawn out into fibrous products which, when fully extended, are of the type of β -keratin (see, for example, Astbury, Dickinson & Bailey 1935; Astbury 1945).