WSSV355 enhances IDH1 enzymatic activity and promotes efficient WSSV replication.

White spot syndrome virus (WSSV) drives extensive metabolic reprogramming to support viral replication, including activation of reductive carboxylation, a pathway in which host isocitrate dehydrogenase 1 (IDH1) has a central role. However, the mechanisms by which viral factors regulate IDH1 and associated metabolic networks remain unclear. Here, we identified WSSV355 as a key viral regulator that contributed to IDH1 binding and activation during infection. Using yeast two-hybrid screening, WSSV355 was identified as an LvIDH1-interacting protein and further validated by co-immunoprecipitation and co-localization analyses. Functional assays demonstrated that WSSV355 enhanced IDH1 enzymatic activity, whereas truncation mapping revealed that distinct regions of WSSV355 contributed to IDH1 binding and activation. In vivo silencing of WSSV355 suppressed viral gene expression, and decreased viral genome copy number, establishing its role in promoting efficient WSSV replication. Affinity purification-mass spectrometry (AP-MS) further revealed that WSSV355 identified a set/network of WSSV355-associated proteins enriched in cytoskeletal, RNA-processing, and metabolic pathways. Integration with infection-responsive proteomic datasets identified candidate modules linking the WSSV355-associated protein network to host infection responses, suggesting broader potential involvement of WSSV355 in host cellular processes during infection. Collectively, these findings identify WSSV355 as an LvIDH1-interacting viral protein that enhances IDH1 enzymatic activity and is required for efficient WSSV replication. To our knowledge, WSSV355 is the first reported virus-encoded protein shown to enhance IDH1 enzymatic activity, providing new insights into how aquatic viruses exploit host metabolic machinery to promote infection.