Viral fusion protein transmembrane domain adopts β-strand structure to facilitate membrane topological changes for virus-cell fusion.
The C-terminal transmembrane domain (TMD) of viral fusion proteins such as HIV gp41 and influenza hemagglutinin (HA) is traditionally viewed as a passive α-helical anchor of the protein to the virus envelope during its merger with the cell membrane. The conformation, dynamics, and lipid interaction of these fusion protein TMDs have so far eluded high-resolution structure characterization because of their highly hydrophobic nature. Using magic-angle-spinning solid-state NMR spectroscopy, we show that the TMD of the parainfluenza virus 5 (PIV5) fusion protein adopts lipid-dependent conformations and interactions with the membrane and water. In phosphatidylcholine (PC) and phosphatidylglycerol (PG) membranes, the TMD is predominantly α-helical, but in phosphatidylethanolamine (PE) membranes, the TMD changes significantly to the β-strand conformation. Measured order parameters indicate that the strand segments are immobilized and thus oligomerized. (31)P NMR spectra and small-angle X-ray scattering (SAXS) data show that this β-strand-rich conformation converts the PE membrane to a bicontinuous cubic phase, which is rich in negative Gaussian curvature that is characteristic of hemifusion intermediates and fusion pores. (1)H-(31)P 2D correlation spectra and (2)H spectra show that the PE membrane with or without the TMD is much less hydrated than PC and PG membranes, suggesting that the TMD works with the natural dehydration tendency of PE to facilitate membrane merger. These results suggest a new viral-fusion model in which the TMD actively promotes membrane topological changes during fusion using the β-strand as the fusogenic conformation.
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139;
Hongwei
H
Yao
Department of Bioengineering, California NanoScience Institute, University of California, Los Angeles, CA 90095;
Michelle W
http://orcid.org/0000-0003-1613-9501
MW
Lee
Department of Physiology and Biophysics, University of California, Irvine, CA 92697; Department of Medicine, Harbor University of California Los Angeles Medical Center, LA BioMed, Torrance, CA 90502.
Alan J
AJ
Waring
Department of Bioengineering, California NanoScience Institute, University of California, Los Angeles, CA 90095;
Gerard C L
GC
Wong
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139; meihong@mit.edu.
Mei
M
Hong
D002459:Cell Fusion; D015700:HIV Envelope Protein gp41 / Q000737:chemistry*; D006389:Hemagglutinins, Viral / Q000737:chemistry*; D008563:Membrane Lipids / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D053838:Scattering, Small Angle; D014760:Viral Fusion Proteins / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
D015700:HIV Envelope Protein gp41; D006389:Hemagglutinins, Viral; D008563:Membrane Lipids; D014760:Viral Fusion Proteins; C514787:gp41 protein, Human immunodeficiency virus 1; D014867:Water
conformational polymorphism; membrane curvature; peptide–membrane interactions; small-angle X-ray scattering; solid-state NMR spectroscopy