Relation between 'Fibrous' and 'Globular' Proteins

Abstract

ON various occasions in NATURE and elsewhere it has been argued that the elastic fibrous proteins, keratin and myosin, by virtue of the system of intramolecular folds which appears to be their characteristic stereochemical feature, are the linear prototype of the globular proteins, which presumably are constructed to similar principles but in two or three dimensions¹. Direct experimental support for this view comes from X-ray studies of the denaturation of the globular proteins, which show that the change always results in the appearance of polypeptide chains, which can often be drawn out into artificial fibres analogous to β-keratin or β-myosin². It has also been recognized for some time that feather keratin³ in particular is to X-rays really both fibrous and globular, and more recently the early observation of long spacings in the keratins has been supplemented by the discovery of even longer spacings in these and other protein fibres⁴. The tobacco mosaic virus⁵ is another protein which has properties both fibrous and globular^*—and, to cut a long story short, it looks now as if the original apparent distinction between the two types is beginning to disappear. One possible way, based on density and other considerations, of deriving a general scheme directly from keratin⁶ amounts actually to building up molecules having essentially the structure deduced from X-ray data for the keratin crystallites, and this suggests at once the idea that the protein fibre crystallites and the tobacco virus units fall into the same category.