Functional Characterization of a Lassa Virus Fusion Inhibitor Adaptive Mutant

Abstract The LASV glycoprotein complex (GPC) contains a retained stable signal peptide (SSP), GP1, and GP2. SSP interacts with GP2 and provides an interface targeted by numerous fusion inhibitors. Serialpassaging of LASV with inhibitors allowed some adaptive mutants to be obtained, most of which had mutations located in the transmembrane (TM) domain of GP2. In the current study, we focused on the F446L mutant, which is reported to confer resistance to ST-series inhibitors. We found that F446L cells conferred cross-resistance to structurally distinct inhibitors. Furthermore, F446L increased the fusion activities of LASV and Mopeia virus GPC, elevating the pH threshold for the fusion of LASV and promoting the fusion of MOPV at neutral pH. F446L had little effect on the growth profile or thermostability of the pseudotype of the virus. By introducing other residues to the conserved F446 locus, it was found that this site was less compatible with a similar tyrosine residue and was intolerant to charged residues. These results help characterize the fusion inhibitor target located in the TM domain of GP2, which should be useful for drug and vaccine design.