Virus Structure

Abstract

It is scarcely more than ten years since we first learned of the fold of a viral protein. The structures of tobacco mosaic virus, by fiber diffraction at 4-Å resolution (Stubbs et al., 1977), and tomato bushy stunt virus by crystallography at 2.9 Å (Harrison et al., 1978) were very different from each other, and at that time it might have been expected that further work would lead only to an ever-increasing array of unrelated structures. In fact, virus structures determined since then have shown a considerable range of variation, but on a suprisingly limited number of themes. In particular, all the spherical viruses whose structures have been determined by crystallography until now have been shown to be related to the original example of bushy stunt virus, even in cases where there is no similarity in amino acid sequence, serology, or host range. At present, there are only three known basic virus coat protein folds: the β barrel of the spherical viruses, the α-helix bundle of the rod-shaped tobamoviruses, and the interleaved α helices of the filamentous bacteriophages. This is not to imply that no more will be found; it does, however, suggest that a few viruses have shown a remarkable capacity to adapt and evolve.