REVERSIBLE PH-DEPENDENT CONFORMATIONAL CHANGE OF RECONSTITUTED INFLUENZA HEMAGGLUTININ

Fusion between influenza virus and cell membranes is mediated bf a maj or add-induced conformational change of the spike glycoprotein of the viral envelope, hemagglutinin (HA) The conformational change of HA is commonly believed to be a kinetically controlled irreversible process, . although the experimental evidence for this is controversial. Here w e show bf polarized infrared spectroscopy that the previously describe d acid-induced inclination of HA reconstituted in supported phospholip id bilayers is reversible in the absence, but irreversible in the pres ence, of bound target membranes. We also demonstrate reversible pH-dep endent changes in the capability of reconstituted HA to bind target me mbranes. These results support a thermodynamically controlled mechanis m of the conformational change of HA and provide new insight into the understanding of the energetics of influenza-mediated membrane fusion. (C) 1996 Academic Press Limited