The La Crosse virus class II fusion glycoprotein loop contributes to infectivity and replication and .

Arthropod-borne viruses (arboviruses) are an emerging and evolving global public health threat, with limited antiviral treatments or vaccines available. La Crosse virus (LACV) from the order is responsible for pediatric encephalitis cases in the United States, yet little is known about the infectivity of LACV. Given the structural similarities between class II fusion glycoproteins of LACV and chikungunya virus (CHIKV), an alphavirus from the family, we hypothesized that LACV would share similar entry mechanisms with CHIKV. To test this hypothesis, we performed cholesterol-depletion and repletion assays and used cholesterol-modulating compounds to study LACV entry and replication. We found that LACV entry was cholesterol dependent, while replication was less affected by cholesterol manipulation. In addition, we generated single-point mutants in the LACV Gc loop that corresponded to known CHIKV residues important for virus entry. We found that a conserved histidine and alanine residue in the Gc loop impaired virus infectivity and attenuated LACV replication and . Finally, we took an evolution-based approach to explore how the LACV glycoprotein evolves in mosquitoes and mice. We found multiple variants that cluster in the Gc glycoprotein head domain, providing evidence for the Gc glycoprotein as a contributor to LACV adaptation. Together, these results begin to characterize the mechanisms of LACV infectivity and how the LACV glycoprotein contributes to replication and pathogenesis. IMPORTANCE Vector-borne viruses are significant health threats that lead to devastating disease worldwide. The emergence of arboviruses, in addition to the lack of effective antivirals or vaccines, highlights the need to study how arboviruses replicate at the molecular level. One potential antiviral target is the class II fusion glycoprotein. Alphaviruses, flaviviruses, and bunyaviruses encode a class II fusion glycoprotein that contains strong structural similarities at the tip of domain II. Here, we show that the bunyavirus La Crosse virus uses a cholesterol-dependent entry pathway similar to the alphavirus chikungunya virus, and residues in the loop are important for virus infectivity and replication in mice. These studies show that genetically diverse viruses may use similar pathways through conserved structure domains, suggesting that these viruses may be targets for broad-spectrum antivirals in multiple arboviral families.