Remodelled cholesteryl ester enriched lipid droplets fuel flavivirus morphogenesis.

Flaviviruses such as dengue and Zika viruses extensively remodel host cell membranes to create specialised replication organelles, but the role of lipid metabolism to generate them remain poorly understood. Through systematic screens of fatty acyl transferase enzymes (MBOAT and zDHHC families) and complementary approaches including CRISPR/Cas9 gene deletions, pharmacological inhibition, proteomics, and photo-crosslinkable cholesterol analogues, we identified cholesteryl ester-enriched lipid droplets (CE-LDs) as critical host components required for flavivirus infection. CE-LD formation is mediated by Sterol O-acyltransferases 1 and 2 (SOAT1/SOAT2), whose activities were upregulated early during infection, coinciding with increased CE-LD formation and transition to liquid crystalline phases. Genetic deletion or pharmacological inhibition of either enzyme resulted in a dramatic ~100-fold reduction in viral production. Mechanistically, CE-LDs display distinct proteomic signatures, enriched in fatty acid remodelling enzymes, GTPases, and lipid transport proteins. Photo-crosslinking experiments demonstrated direct interactions between LD-derived cholesterol and viral prM, capsid and NS1. Disrupting CE-LD formation via SOAT1/2-deficiency resulted in defective, viral RNA-free replication organelles and complete absence of immature virions. Supporting the physiological and clinical relevance of viral LD exploitation, analysis in iPSC-derived macrophages mirrored findings in Huh7 cells, and dengue patients from a Sri Lankan cohort revealed that central obesity significantly increased the risk of severe dengue haemorrhagic fever. This study establishes CE-LDs as essential host metabolic hubs that enable flavivirus morphogenesis and identifies host LD metabolism as a promising therapeutic target for combating flavivirus infections.