Purification and characterization of the reovirus cell attachment protein σ1

Abstract

It has previously been shown that of all the soluble reovirus-specified proteins present in the infected cell lysate, protein σ1 alone possesses the capacity to bind to host cells ( P. W. K. Lee, E. C. Hayes, and W. K. Joklik, 1981, Virology, 108, 156–163). We found that σ1 from urea-disrupted reovirus particles was also capable of such specific binding. Reovirions were therefore used as a source of functional σ1. Accordingly, a simple procedure has been developed to purify σ1 by subjecting urea-disrupted reovirions to DEAE ion-exchange chromatography. Protein σ1 thus isolated was electrophoretically homogeneous and the recovery was estimated to be 50 to 60% of the theoretical yield. The purified protein presumably maintained its native conformation since it was recognized by a panel of monoclonal anti-σ1 antibodies previously isolated, and was capable of specifically binding to host cell receptors, agglutinating human erythrocytes and inducing neutralization and hemagglutination-inhibition antibodies. Subsequent chemical crosslinking studies revealed the presence of oligomeric (mostly dimeric) σ1 forms in the preparation. The amino acid composition of the purified σ1 was found to closely match that inferred from the St gene sequence. However, attempts to determine its amino-terminal sequence have not been successful. The p l of the purified protein was determined to be 6.8. Circular dichroic measurements of the purified σ1 indicated that 54 and 19% of its residues were arranged in α-helical and β-sheet secondary structures, respectively.