Baker’s yeast serves as an ideal model to study endomembrane system due to high conservation of its regulation and trafficking between yeast and human. ENV9 is a novel gene involved in vesicular trafficking in Saccharomyces cerevisiae. Previous characterization by our laboratory established that ENV9 deletion leads to lysosomal defects and that Env9 is localized to lipid droplets (LDs). Our bioinformatics studies show that ENV9 is conserved among eukaryotes and is an orthologue of human Retinol Dehydrogenase 12 ( RDH12).

In this study, we show that Env9 is involved in LD biogenesis by positively regulating LD fusion and glycerol-induced LD proliferation. We establish Env9 to be an oxidoreductase in vitro that displays specific oxidoreductase activity towards RDH12 toxic aldehyde substrate. We also show that Env9 oxidoreductase activity requires its conserved functional domains. Furthermore, we show that oxidoreductase activity is essential for the observed cellular function of Env9 and that interactions with ENV10 may be required for ENV9-dependent promotion of LD fusion.