A glycoprotein mutation that emerged during the 2013-2016 Ebola virus epidemic alters proteolysis and accelerates membrane fusion

Abstract

Genomic surveillance of viral isolates during the 2013-2016 Ebola virus epidemic in Western Africa—the largest and most devastating filovirus outbreak on record—revealed several novel mutations. The responsible strain, named Makona, carries an A to V substitution at position 82 in the glycoprotein (GP), which is associated with enhanced infectivity in vitro. Here, we investigated the mechanistic basis for this enhancement, as well as the interplay between A82V and a T to I substitution at residue 544 of GP, which also modulates infectivity in cell culture. We found that both 82V and 544I destabilize GP with the residue at 544 impacting overall stability, while 82V specifically destabilizes proteolytically cleaved GP. Both residues also promote faster kinetics of lipid mixing of the viral and host membranes in live cells, individually and in tandem, which correlates with faster times to fusion following co-localization with the viral receptor Niemann-Pick C1 (NPC1). Further, GPs bearing 82V are more sensitive to proteolysis by cathepsin L (CatL), a key host factor for viral entry. Intriguingly, CatL processed 82V variant GPs to a novel product of ~12K size, which we hypothesize corresponds to a form of GP more fully primed for fusion than previously detected. We thus propose a model in which 82V promotes more efficient GP processing by CatL, leading to faster viral fusion kinetics and higher infectivity.

Pathogenicity and Virulence of Ebolaviruses with Species- and Variant-specificity

“…This was due to the emergence of the A82V mutation at the branch point that distinguishes two lineages and was fixed in the population afterward [182][183][184][185][186], and residue 82 on GP is located at the receptor-binding interface [187]. Several in vitro studies using EBOV GP-pseudotyped virus vectors or EBOV VLP systems have demonstrated that GP-A82V promotes viral entry into human cells [182,183,188], by which the mechanisms were further identified as cathepsin B and Niemann-Pick C1 dependent [189,190]. Interestingly, the enhancement of viral entry mediated by GP-A82V was only observed in primate cells, but not in rodent, carnivore [182], or batorigin cells [183,191], suggesting that the A82V mutation might have contributed to elevated EBOV-Makona fitness in human population.…”