Abstract
Ceramidases catalyze the conversion of ceramide to sphingosine. They are acylaminohydrolases that catalyze the deacylation of the amide-linked saturated fatty acid from ceramide to generate sphingosine. They also catalyze the reverse reaction of ceramide biosynthesis using sphingosine and fatty acid. In mammals, different proteins catalyze these reactions while individually exhibiting optimal activity over a narrow pH range and have been accordingly called acid, neutral, and alkaline ceramidases. Several genes encode for variants of alkaline ceramidase in mammals. Brainwashing (Bwa) is the only putative alkaline ceramidase homologue present in Drosophila. In this study we have demonstrated that BWA does not exhibit ceramidase activity and that bwa null mutants display no loss of ceramidase activity. Instead, the neutral ceramidase gene CDase encodes the protein that is responsible for all measurable ceramidase activity in Drosophila. Our studies show strong genetic interaction of Bwa with CDase and the Drosophila ceramide kinase gene (DCERK). We show that, although BWA is unlikely to be a ceramidase, it is a regulator of sphingolipid flux in Drosophila. Bwa exhibits strong genetic interaction with other genes coding for ceramide-metabolizing enzymes. This interaction might partly explain its original identification as a ceramidase.