Studies using double mutants of the conformational transitions in influenza hemagglutinin required for its membrane fusion activity.
Amino acid substitutions widely distributed throughout the influenza hemagglutinin (HA) influence the pH of its membrane fusion activity. We have combined a number of these substitutions in double mutants and determined the effects on the pH of fusion and on the pH at which the refolding of HA required for fusion occurs. By analyzing combinations of mutations in three regions of the metastable neutral-pH HA that are rearranged at fusion pH we obtain evidence for both additive and nonadditive effects and for an apparent order of dominance in the effects of amino acid substitutions in particular regions on the pH of fusion. We conclude that there are at least three components in the structural transition required for membrane fusion activity and consider possible pathways for the transition in relation to the known differences between neutral and fusion pH HA structures.
National Institute for Medical Research, Mill Hill, London, United Kingdom.
D A
DA
Steinhauer
J
J
Martín
Y P
YP
Lin
S A
SA
Wharton
M B
MB
Oldstone
J J
JJ
Skehel
D C
DC
Wiley
D001224:Aspartic Acid; D005998:Glycine; D006367:HeLa Cells; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000096:biosynthesis / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D008081:Liposomes; D046911:Macromolecular Substances; D008561:Membrane Fusion; D008961:Models, Structural; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D014357:Trypsin
D019267:Hemagglutinin Glycoproteins, Influenza Virus; D008081:Liposomes; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D001224:Aspartic Acid; D014357:Trypsin; D005998:Glycine