The filovirus surface glycoprotein (GP) mediates viral entry into host cells. Following viral internalization into endosomes, GP is cleaved by host cysteine proteases to expose a receptor binding site (RBS) otherwise hidden from immune surveillance. Here we present the crystal structure of proteolytically cleaved Ebola virus GP to a resolution of 3.3 Å. We use this structure in conjunction with functional analysis of a large panel of pseudotyped viruses bearing mutant GP proteins to map the Ebola virus GP endosomal RBS at molecular resolution. Our studies indicate that binding of GP to its endosomal receptor Niemann-Pick C1 occurs in two distinct stages: initial electrostatic interactions, followed by specific interactions with a hydrophobic trough exposed on the endosomally cleaved GP1 subunit. Finally, we demonstrate that monoclonal antibodies targeting the filovirus RBS neutralize all known filovirus GPs, making this conserved pocket a promising target for the development of pan-filovirus therapeutics.
IMPORTANCE
Ebola virus uses its glycoprotein GP to enter new host cells. During entry, GP must be cleaved by human enzymes in order for receptor binding to occur. Here we provide the crystal structure of the cleaved form of Ebola virus GP We demonstrate that cleavage exposes a site at the top of GP and demonstrate that this site binds the critical domain C of the receptor, termed Niemann Pick C1, NPC1. We perform mutagenesis to find parts of the site essential for binding NPC1 and map distinct roles for an upper, charged crest and lower, hydrophobic rough in cleaved GP. We find that this three-dimensional site is conserved across the filovirus family and that antibody directed against this site is able to bind cleaved GP form every filovirus tested and neutralize viruses bearing those GPs.
