Ion channels in southern bean mosaic virus capsid.

The study of southern bean mosaic virus protein coat high resolution model revealed a structure with properties of a natural protein-ion channel. Coat protein pentamers form a 30-A long channel and the amino acid composition of its wall bears some homology with the pentameric structure proposed for the nicotinic acetylcholine receptor channel. Ion transport properties were analyzed by computing ion-protein interaction energies on the basis of quantum chemistry methods. Energy maps show a channel attractive for cations, fully permeable to Li(+) and a narrow barrier for other cations and water. The energy profiles found are similar to the profiles determined for the K(+) channel of the sarcoplasmic reticulum. Comparisons with other icosahedral virus structures, including picornaviruses, suggest that ion channels would be a common feature of viral capsids. Biological roles for these channels are proposed.