Studies of influenza haemagglutinin-mediated membrane fusion.

A resonance energy transfer assay of membrane fusion developed by P. S. Uster and D. W. Deamer (Biochemistry 24, 1-8 (1985)) was used in a study of influenza haemagglutinin-mediated fusion. The characteristics of fusion and haemolysis by X-31 (H3N2) virus, a number of mutants of X-31 which fuse membranes at higher pH, and purified haemagglutinins released from virus particles either by detergent dissociation or by bromelain digestion were compared with particular regard to pH and temperature dependence. The finding that membrane fusion activity, haemolysis, and changes in haemagglutinin conformation covary with pH and temperature provide support for the role of haemagglutinin in fusion and are discussed in relation to the stability of its structure.