Purification and amino acid compositions of the structural proteins of Sindbis virus

Abstract

The envelope glycoproteins El and E2 of Sindbis virus (a member of the alphavirus group of the Toga virus family) have been purified on the basis of their differential binding to glass wool in the presence of the nondenaturing detergent Triton X-100, and milligram amounts of all three structural proteins of the virus have been prepared. The amino acid compositions of these proteins have been determined for two strains of the virus, wt and HR. Although it is clear from other studies that one or more structural proteins of the heat-resistant variant have been altered relative to the wild type, we were unable to detect such changes at the level of amino acid composition. As expected, the capsid protein is rich in the basic amino acids, and in this respect shows a strong similarity to the capsid protein of the closely related Semliki Forest virus. The molecular weight of the capsid protein has been estimated from the composition data to be 30,000 ± 600 daltons, in good agreement with the results obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The envelope proteins El and E2 contain a proportion of polar amino acids which is typical of water-soluble proteins, with no apparent excess of amino acids with hydrophobic side chains. Thus it is unlikely that extensive regions of these proteins are buried in the hydrophobic interior of the lipid bilayer of the viral envelope.

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