Role of LAMP1 Binding and pH Sensing by the Spike Complex of Lassa Virus

Abstract

To effectively infect cells, Lassa virus needs to switch in an endosomal compartment from its primary receptor, ␣-dystroglycan, to a protein termed LAMP1. A unique histidine triad on the surface of the receptor-binding domain from the glycoprotein spike complex of Lassa virus is important for LAMP1 binding. Here we investigate mutated spikes that have an impaired ability to interact with LAMP1 and show that although LAMP1 is important for efficient infectivity, it is not required for spike-mediated membrane fusion per se. Our studies reveal important regulatory roles for histidines from the triad in sensing acidic pH and preventing premature spike triggering. We further show that LAMP1 requires a positively charged His230 residue to engage with the spike complex and that LAMP1 binding promotes membrane fusion. These results elucidate the molecular role of LAMP1 binding during Lassa virus cell entry and provide new insights into how pH is sensed by the spike. IMPORTANCELassa virus is a devastating disease-causing agent in West Africa, with a significant yearly death toll and severe long-term complications associated with its infection in survivors. In recent years, we learned that Lassa virus needs to switch receptors in a pHdependent manner to efficiently infect cells, but neither the molecular mechanisms that allow switching nor the actual effects of switching were known. Here we investigate the activity of the viral spike complex after abrogation of its ability to switch receptors. These studies inform us about the role of switching receptors and provide new insights into how the spike senses acidic pH.

Lassa Virus Cell Entry Reveals New Aspects of Virus-Host Cell Interaction

“…Recent electron cryotomography studies on authentic LASV particles revealed conformational changes in GP1 to occur under pH 5, in line with the X-ray data (66). Although LAMP1 is crucial for productive LASV entry (64), LAMP1 binding is not strictly required for fusion per se, evidenced by mutations within the histidine triad that were still able to undergo fusion, albeit at lower pH (67). Elegant functional studies demonstrated that residue H230 within the histidine triad on LASV GP1 undergoes protonation around pH 5.5, when GP1 starts dissociating from DG (Fig.…”

Mutational Analysis of Lassa Virus Glycoprotein Highlights Regions Required for Alpha-Dystroglycan Utilization

“…7A). Previous work by Cohen-Dvashi et al tested Fusion activity individual mutations H92Y, H93Y, and H230Y for processing, surface expression, and fusion activity (30). When they individually changed each histidine to tyrosine, they found a reduction in the level of cleaved, surface-expressed GP but no significant changes in cell-cell fusion.…”

“…The transduction defect in HAP1 cells with no defect in HAP1 ΔDAG1 cells suggests that F147 is important for efficient ␣DG utilization. Fourteen conserved charged residues were mutated to alanine, including a described histidine triad (H92, H93, and H230), which has been implicated in LAMP1 interaction (30,33). All mutated GPs were cleaved and transported to the cell membrane at levels greater than 60% of parental GP (Fig.…”

“…To determine if combining some of the individual mutations that modestly decreased HAP1 entry would synergistically eliminate ␣DG binding, two double mutants that incorporated mutations at GP residues 141 and 147 were made. Constructs with H92Y-H93Y and H230Y mutations were also made to compare the effects of alanine versus tyrosine substitutions and to reproduce similar constructs tested in the study by Cohen-Dvashi et al (30,33). Overall, surface expression and processing of the additional targeted mutants were near wild-type LASV GP levels with the exception of H92Y-H93Y and H141N-F147A mutants.…”

The involvement of epithelial cells in arenavirus-induced pathogenesis.

“…Binding of LAMP1 is driven by a triad of histidines on the GP1 and that binding of LAMP1 triggers the LASV spike to catalyze membrane fusion by potentiating its response to pH [29,48]. While this histidine triad is conserved among other OW arenaviruses, LAMP-1 utilization has been shown to be specific for LASV, and LAMP1 is not utilized by LCMV or other OW arenaviruses, regardless of α-DG affinity [27,49].…”