Electron microscopy of antibody complexes of influenza virus haemagglutinin in the fusion pH conformation.

AUTOR(ES)

Wharton, S A

RESUMO

Activation of the membrane fusion potential of influenza haemagglutinin (HA) at endosomal pH requires changes in its structure. X-ray analysis of TBHA2, a proteolytic fragment of HA in the fusion pH conformation, indicates that at the pH of fusion the 'fusion peptide' is displaced by > 10 nm from its location in the native structure to the tip of an 11 nm triple-stranded coiled coil, and that the formation of this structure involves extensive re-folding or reorganization of HA. Here we examine the structure of TBHA2 with the electron microscope and compare it with the fusion pH structure of HA2 in virosomes, HA2 in aggregates formed at fusion pH by the soluble, bromelain-released ectodomain BHA and HA2 in liposomes with which BHA associates at fusion pH. We have oriented each HA2 preparation for comparison, using site-specific monoclonal antibodies. We conclude that the structural changes in membrane-anchored and soluble HA preparations at the pH of fusion appear to be the same; that in the absence of a target membrane, the 'fusion peptide' of HA in virosomes associates with the virosome membrane so that HA2 is membrane bound at both N- and C-termini, which implies that inversion of the re-folded HA can occur; and that the structural changes observed by X-ray analysis do not result from the proteolytic digestions used in the preparation of TBHA2.

Documentos Relacionados

• Changes in the conformation of influenza virus hemagglutinin at the pH optimum of virus-mediated membrane fusion.
• Fusion of influenza virus membranes with liposomes at pH 7.5.
• Biological function of the low-pH, fusion-inactive conformation of rabies virus glycoprotein (G): G is transported in a fusion-inactive state-like conformation.
• Variant influenza virus hemagglutinin that induces fusion at elevated pH.
• The structure of a membrane fusion mutant of the influenza virus haemagglutinin.