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Journal of Virology, June 1999, p. 4567-4574, Vol. 73, No. 6
Laboratory of Experimental and Computational
Biology, National Cancer Institute
Received 6 January 1999/Accepted 24 February 1999
Three strains of influenza virus (H1, H2, and H3) exhibited similar
characteristics in the ability of their hemagglutinin (HA) to induce
membrane fusion, but the HAs differed in their susceptibility to
inactivation. The extent of inactivation depended on the pH of
preincubation and was lowest for A/Japan (H2 subtype), in agreement
with previous studies (A. Puri, F. Booy, R. W. Doms, J. M. White, and R. Blumenthal, J. Virol. 64:3824-3832, 1990). While
significant inactivation of X31 (H3 subtype) was observed at 37°C at
pH values corresponding to the maximum of fusion (about pH 5.0), no
inactivation was seen at preincubation pH values 0.2 to 0.4 pH units
higher. Surprisingly, low-pH preincubation under those conditions
enhanced the fusion rates and extents of A/Japan as well as those of
X31. For A/PR 8/34 (H1 subtype), neither a shift of the pH (to >5.0)
nor a decrease of the temperature to 20°C was sufficient to prevent
inactivation. We provide evidence that the activated HA is a
conformational intermediate distinct from the native structure and from
the final structure associated with the conformational change of HA,
which is implicated by the high-resolution structure of the soluble
trimeric fragment TBHA2 (P. A. Bullough, F. M. Hughson,
J. J. Skehel, and D. C. Wiley, Nature 371:37-43, 1994).
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Conformational Intermediates and Fusion Activity of
Influenza Virus Hemagglutinin
Frederick Cancer Research & Development Center, National Institutes of Health, Frederick, Maryland
217021;
Mathematisch-Naturwissenschaftliche Fakultät I, Institut
für Biologie/Biophysik, Humboldt-Universität zu Berlin,
D-10115 Berlin, Germany2; and
National Institute of Arthritis and Musculoskeletal and Skin
Disease, National Institutes of Health, Bethesda, Maryland
208923
*
Corresponding author. Mailing address for A. Herrmann:
Mathematisch-Naturwissenschaftliche Fakultät I, Institut
für Biologie/Biophysik, Humboldt-Universität zu Berlin,
Invalidenstr. 43, D-10115 Berlin, Germany. Phone: 49-30-20938860. Fax:
49-30-20938585. E-mail: Andreas=Herrmann{at}rz.hu-berlin.de. Mailing address for R. Blumenthal: Laboratory of Experimental and
Computational Biology, National Cancer Institute-FCRDC, National Institutes of Health, Bldg. 469, Rm. 211, Frederick, MD 21702. Phone:
(301) 846-5068. Fax: (301) 846-6192. E-mail:
blumen{at}helix.nih.gov.
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