Conformation and Trimer Association of the Transmembrane Domain of the Parainfluenza Virus Fusion Protein in Lipid Bilayers from Solid-State NMR: Insights into the Sequence Determinants of Trimer Structure and Fusion Activity.

ABSTRACT: Enveloped viruses enter cells by using their fusion proteins to merge the virus lipid envelope and the cell membrane. While crystal structures of the water-soluble ectodomains of many viral fusion proteins have been determined, the structure and assembly of the C-terminal transmembrane domain (TMD) remains poorly understood. Here we use solid-state NMR to determine the backbone conformation and oligomeric structure of the TMD of the parainfluenza virus 5 fusion protein. 13C chemical shifts indicate that the central leucine-rich segment of the TMD is ?-helical in POPC/cholesterol membranes and POPE membranes, while the Ile- and Val-rich termini shift to the ?-strand conformation in the POPE membrane. Importantly, lipid mixing assays indicate that the TMD is more fusogenic in the POPE membrane than in the POPC/cholesterol membrane, indicating that the ?-strand conformation is important for fusion by inducing membrane curvature. Incorporation of para-fluorinated Phe at three positions of the ?-helical core allowed us to measure interhelical distances using 19F spin diffusion NMR. The data indicate that, at peptide:lipid molar ratios of ~1:15, the TMD forms a trimeric helical bundle with inter-helical distances of 8.2-8.4Å for L493F and L504F and 10.5Å for L500F. These data provide high-resolution evidence of trimer formation of a viral fusion protein TMD in phospholipid bilayers, and indicate that the parainfluenza virus 5 fusion protein TMD harbors two functions: the central ?-helical core is the trimerization unit of the protein, while the two termini are responsible for inducing membrane curvature by transitioning to a ?-sheet conformation.

SUBMITTER: Lee M 

PROVIDER: S-EPMC5831503 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature