Functional characterization of fatty acid synthase in Hermetia illucens

Fatty acid synthase (FAS) is a key role in de novo lipogenesis (DNL) in most lives. In insects, type I FAS functions in homodimer, activated by a phosphopantetheine transferase (PPT), to de novo produce essential saturated fatty acid for cellular processes. In a nova insect species Hermetia illucens (Diptera: Stratiomyidae), different from most animals and insects, lauric acid (LA) accumulates to a noticeable level, near content of that in coconut oil or palm kernel oil. However, the origin of LA, from de novo biosynthesis or as degraded products from long chain fatty acid, was still ambiguous. Here, in this study, we mined a FAS genes (HiOGS16234) from H. illucens genome and initially characterized its abilities of LA production in a free-fatty-acid producible yeast. After clear the yeast metabolites background of fatty acid by deletion of ScFAS1 and ScELO1 sequentially, which responsible for fatty acid genesis and elongation respectively, functions of HiOGS16234 from H. illucens was in vitro elucidated by analyzing its product portfolio. Through protein domain swap in HiOGS16234, we found the ketoacyl synthase domain and thioesterases domain were responsible for the different product portfolio of HiOGS16234, compared with DmFASN1. Through in vitro assay in yeast, the origin of LA in BSF was firstly elucidated at molecular level, which support DNL origin hypothesis in BSF.