Conformation and stability of Sendai virus fusion protein

Abstract

The conformation and stability of Sendai virus fusion (F) protein were studied by circular dichroism spectroscopy, and the protein predictive models of Chou and Fasman and Robson and Suzuki were used to elucidate the secondary structure of Sendai virus F protein. The F protein conformation is predicted to contain 33% α-helix, 53% β-sheet and 15% β-turn by the Chou and Fasman model, and 30% α-helix, 55% β-sheet, 9% β-turn and 7% random coil by the Robson and Suzuki model, C.d. studies of F protein purified in the presence of the non-ionic detergent, n-octylglucoside, indicated the presence of 49% α-helix and 31% β-sheet at pH 7.0, 54% α-helix and 28% β-sheet at pH 9.0 and 50% α-helix and 23% β-sheet at pH 5.4. A small change in conformation of the protein occurred when the pH was titrated from 7.0 to 5.4 and from 7.0 to 9.0 and a more pronounced conformational change occured when the pH was changed from 9.0 to 5.4. The F protein in 0.2% n-octylglycoside was resistant to denaturation by 4 m guanidine hydrochloride, the reducing agent 20 m m mercaptoethanol, and to increases in temperature from 5 to 80°C. Monoclonal anti-F protein antibody showed an increased binding to whole virus when the pH was changed from 7.0 to 9.0. The antibody binding was decreased when the pH was shifted from 9.0 to 5.4. Maximum haemolytic activity was observed with virus that was preincubated at pH 8.0. The enhanced haemolytic activity could be correlated with a small conformational change in the fusion protein at basic pH, as determined by the c.d. spectrum and the antibody binding data from enzyme-linked immunoadsorbent assay. These results represent the first report of a conformational change in Sendai virus F protein when the pH was changed from basic to acidic pH.