TY - JOUR
T1 - pH-induced alterations in the fusogenic spike protein of semliki forest virus
AU - Kielian, Margaret
AU - Helenius, Ari
PY - 1985/12/1
Y1 - 1985/12/1
N2 - The spike glycoproteins of Semliki Forest virus mediate membrane fusion between the viral envelope and cholesterol-containing target membranes under conditions of mildly acidic pH (pH < 6.2). The fusion reaction is critical for the infectious cycle, catalyzing virus penetration from the acidic endosome compartment. To define the role of the viral spike glycoproteins in the fusion reaction, conformational changes in the spikes at acid pH were studied using protease digestion and binding assays to liposomes and nonionic detergent. A method was also developed to prepare fragments of both transmembrane subunit glycopolypeptides of the spike, E1 and E2, which lacked the hydrophobic anchor peptides. Unlike the intact spikes the fragments were monomeric and therefore useful for obtaining information on conformational changes in individual subunits. The results showed that both E1 and E2 undergo irreversible conformational changes at the pH of fusion, that the conformational change of E1 depends, in addition to acidic pH, on the presence of cholesterol, and that no major changes in the solubility properties of the spikes takes place. On the basis of these findings it was concluded that fusion involves both subunits of the spike and that E1 confers the stereo-specific sterol requirement. The results indicated, moreover, that acid-induced fusion of Semliki Forest virus differs in important respects from that of influenza virus, another well-defined model system for protein-mediated membrane fusion.
AB - The spike glycoproteins of Semliki Forest virus mediate membrane fusion between the viral envelope and cholesterol-containing target membranes under conditions of mildly acidic pH (pH < 6.2). The fusion reaction is critical for the infectious cycle, catalyzing virus penetration from the acidic endosome compartment. To define the role of the viral spike glycoproteins in the fusion reaction, conformational changes in the spikes at acid pH were studied using protease digestion and binding assays to liposomes and nonionic detergent. A method was also developed to prepare fragments of both transmembrane subunit glycopolypeptides of the spike, E1 and E2, which lacked the hydrophobic anchor peptides. Unlike the intact spikes the fragments were monomeric and therefore useful for obtaining information on conformational changes in individual subunits. The results showed that both E1 and E2 undergo irreversible conformational changes at the pH of fusion, that the conformational change of E1 depends, in addition to acidic pH, on the presence of cholesterol, and that no major changes in the solubility properties of the spikes takes place. On the basis of these findings it was concluded that fusion involves both subunits of the spike and that E1 confers the stereo-specific sterol requirement. The results indicated, moreover, that acid-induced fusion of Semliki Forest virus differs in important respects from that of influenza virus, another well-defined model system for protein-mediated membrane fusion.
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U2 - 10.1083/jcb.101.6.2284
DO - 10.1083/jcb.101.6.2284
M3 - Article
C2 - 3905823
AN - SCOPUS:0022273625
SN - 0021-9525
VL - 101
SP - 2284
EP - 2291
JO - Journal of Cell Biology
JF - Journal of Cell Biology
IS - 6
ER -