Intermediates in influenza virus PR/8 haemagglutinin-induced membrane fusion.
The fusion kinetics with erythrocyte ghosts of two influenza A virus strains, A/Aichi/2/68 (X:31) and A/PR/8/34 (PR/8), were compared and correlated with the kinetics of haemagglutinin (HA) conformational change. Previously it had been shown that X:31 fuses with liposomes or erythrocytes at 4 degrees C, pH 5 after a lag time of 5 to 10 min whereas PR/8 displayed no fusion with liposomes at that temperature. We have confirmed the absence of cold fusion by PR/8 with erythrocyte ghosts. In contrast to X:31, PR/8 could not be committed to fuse at neutral pH and 37 degrees C by a preincubation at low pH and 4 degrees C. To examine whether the lack of commitment and cold fusion were due to a failure of PR/8 HA to undergo conformational changes at low temperature and pH, we analysed susceptibility of HA to proteinase K digestion, liposome binding to the virus, and immunoprecipitations of HA with conformation-specific antibodies. Although there was little binding of PR/8 to liposomes at 4 degrees C and pH 5, we did observe exposure of the fusion peptide. This study reveals a low temperature intermediate in membrane fusion exhibited by the HA of influenza virus strain PR/8, which involves low pH-induced conformational changes including exposure of the fusion peptide with little interaction of HA with the target membrane.
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Section of Membrane Structure and Function, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
Krumbiegel
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Blumenthal
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R
D000595:Amino Acid Sequence; D004910:Erythrocyte Membrane / Q000378:metabolism; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D006389:Hemagglutinins, Viral / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009980:Influenza A virus / Q000502:physiology*; D008561:Membrane Fusion; D008969:Molecular Sequence Data; D011487:Protein Conformation; D013696:Temperature
D019267:Hemagglutinin Glycoproteins, Influenza Virus; D006389:Hemagglutinins, Viral