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Cell. 2018 Aug 9;174(4):926-937.e12. doi: 10.1016/j.cell.2018.05.050. Epub 2018 Jun 28.

Direct Visualization of the Conformational Dynamics of Single Influenza Hemagglutinin Trimers.

Author information

1
Department of Molecular Biology and Microbiology, Tufts University School of Medicine and Sackler School of Graduate Biomedical Sciences, Boston, MA 02111, USA. Electronic address: dibyendu_kumar.das@tufts.edu.
2
Department of Molecular Biology and Microbiology, Tufts University School of Medicine and Sackler School of Graduate Biomedical Sciences, Boston, MA 02111, USA.
3
Werner Reichardt Centre for Integrative Neuroscience, University of Tuebingen, 72076 Tuebingen, Germany.
4
Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.
5
Departments of Biology and Chemistry, Pharmacy, and Geosciences, Johannes Gutenberg-University Mainz, Johannes-von-Mullerweg 6, 55128 Mainz, Germany; Institute of Molecular Biology (IMB), Ackermannweg 4, 55128 Mainz, Germany; Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany.
6
Department of Molecular Biology and Microbiology, Tufts University School of Medicine and Sackler School of Graduate Biomedical Sciences, Boston, MA 02111, USA. Electronic address: james.munro@tufts.edu.

Abstract

Influenza hemagglutinin (HA) is the canonical type I viral envelope glycoprotein and provides a template for the membrane-fusion mechanisms of numerous viruses. The current model of HA-mediated membrane fusion describes a static "spring-loaded" fusion domain (HA2) at neutral pH. Acidic pH triggers a singular irreversible conformational rearrangement in HA2 that fuses viral and cellular membranes. Here, using single-molecule Förster resonance energy transfer (smFRET)-imaging, we directly visualized pH-triggered conformational changes of HA trimers on the viral surface. Our analyses reveal reversible exchange between the pre-fusion and two intermediate conformations of HA2. Acidification of pH and receptor binding shifts the dynamic equilibrium of HA2 in favor of forward progression along the membrane-fusion reaction coordinate. Interaction with the target membrane promotes irreversible transition of HA2 to the post-fusion state. The reversibility of HA2 conformation may protect against transition to the post-fusion state prior to arrival at the target membrane.

KEYWORDS:

membrane fusion; protein dynamics; single-molecule fluorescence; smFRET; virus entry

PMID:
29961575
PMCID:
PMC6086748
[Available on 2019-08-09]
DOI:
10.1016/j.cell.2018.05.050

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