An architecture for the fusion site of influenza hemagglutinin.

The recent finding that more than one Influenza hemagglutinin (HA) is required at the fusion site for HA-expressing fibroblasts, together with the crystal structure of HA at neutral pH, provide the basic elements of a plausible model for this fusion site. Within an aggregate of HA trimers at low pH, we propose fusion intermediates which are based upon a minimal alteration to the known neutral pH structure of HA and which should have reasonable activation energies. This is the first model of a glycoprotein-mediated fusion site which explicitly accounts for the disposition of the lipids within these intermediates. While the fusion site created by HA will not be the same as that of eukaryotic fusion complexes, general characteristics could be shared.