Structural insights into VLDLR recognition by western equine encephalitis virus.

Western equine encephalitis virus (WEEV), a group of encephalitic alphaviruses that cause severe diseases in humans and equids, historically used the very-low-density lipoprotein receptor (VLDLR) as a receptor during infection. However, current epidemic strains no longer use VLDLR as a receptor. In this study, we identify that LA1, LA2, LA3, and LA5 of VLDLR can directly interact with WEEV. Using cryo-electron microscopy, we investigate the structures of complexes formed between WEEV and VLDLR-LBD or other VLDLR fragments. Our findings show that LA1 and LA2 insert into a cleft formed by two adjacent E2-E1 heterodimers within a single trimeric spike, while LA3 and LA5 interact with the DIII region of WEEV E1. Among VLDLR concatemers, the LA1-5 exhibits the strongest binding affinity for WEEV. Additionally, we find that a single polymorphism in the E2 glycoprotein determines WEEV's receptor tropism. Mutations E2E181K or E2E81K in the nonpathogenic strain Imperial-181 enhanced its ability to enter via VLDLR. These results enhance our understanding of alphavirus receptor recognition and receptor usage shifts, providing insights for the development of antiviral therapies.