Structure of influenza haemagglutinin at neutral and at fusogenic pH by electron cryo-microscopy

The three-dimensional structures of the complete haemagglutinin (MA) of inf luenza virus A/Japan/305/57 (H2N2) in its native (neutral pH) and membrane fusion-competent (low pH) form by electron cryo-microscopy at resolution of 10 Angstrom and 14 Angstrom, respectively, have been determined, In the fu sion-competent form the subunits remain closely. associated preserving typi cal overall features of the trimeric ectodomain at neutral pH. Rearrangemen ts of the tertiary structure in the distal and the stent parts are associat ed with the formation of a central cavity through the entire ectodomain, We suggest that the cavity is essential for relocation of the so-called fusio n sequence of HA towards the target membrane. (C) 1999 Federation of Europe an Biochemical Societies.