Post Fusion Structure of the Transmembrane Domain of the Ebola Virus Surface Glycoprotein

Abstract

Ebola virus (Ebov) is an enveloped virus causing hemorrhagic fever in humans and non-human primates with extremely high fatality rates. Fusion occurs when the virus reaches the endosomal compartment where the surface glycoprotein (GP) undergoes proteolytic cleavage and rearrangement. In this study we focus on the role of the transmembrane (TM) and membrane proximal (MPER) domains of Ebov GP in the fusion process. NMR spectroscopy was performed on a construct comprising Ebov TM and MPER (residues 632-676) to investigate its structure and role in fusion. Solution NMR studies show that the structure is composed of two helices. A dynamic N-terminal region (residues 632-642) is followed by a short MPER helix residing on the surface of the membrane (residues 643-651), a turn (residues 652-657), and the TM helix (residues 658-676). HSQC spectra of Ebov TM/MPER at pre- and post-fusion pH were similar suggesting a pH-independent role of this domain in fusion. Titration experiments revealed a binding site between the FL and TM domains at pH 5.5. The binding site is rich in aromatic residues on the TM (WTGW) and FL (YWTTQD) side. Liposome fusion assays showed that lipid mixing was enhanced when the liposomes contained Ebov TM/MPER. Taken together, we conclude that the Ebov TM/MPER and FL domains cooperate in fusion, but that only the FL structure [see refs. 1 and 2] responds to pH in this process.1. Gregory et al. PNAS (2011) 108:11211-11216.2. Gregory et al. J. Virol. (2014) 88:6636-6649.