Ready…set…fuse

The fusion of two lipid membranes underlies a huge range of biological phenomena, from infection by enveloped viruses to the secretion of cellular proteins, but a central aspect of membrane fusion has remained mysterious: do the proteins that mediate fusion act cooperatively or independently? On page 833, Markovic et al. argue that teamwork is the order of the day in the widely studied model of influenza virus hemagglutinin (HA)-mediated fusion, and suggest that similar cooperative mechanisms may be a general feature of membrane fusion.

At low pH, trimers of HA undergo a conformational transition to mediate fusion between the viral envelope membrane and the membrane of a lysosome, allowing the virus to enter the cytoplasm. Using several approaches in different systems, the authors varied the density of HA trimers on membrane surfaces and measured the speed and efficiency of the conformational...