Glucosylceramide synthases, a gene family responsible for the biosynthesisof glucosphingolipids in animals, plants, and fungi

Glucosylceramides are membrane lipids in most eukaryotic organisms and in a few bacteria. The physiological functions of these glycolipids have only b een documented in mammalian cells, whereas very little information is avail able of their roles in plants, fungi, and bacteria. In an attempt to establ ish appropriate experimental systems to study glucosylceramide functions in these organisms, we performed a systematic functional analysis of a glycos yltransferase gene family with members of animal, plant, fungal, and bacter ial origin. Deletion of such putative glycosyltransferase genes in Candida albicans and Pichia pastoris resulted in the complete loss of glucosylceram ides. When the corresponding knock-out strains were used as host cells for homologous or heterologous expression of candidate glycosyltransferase gene s, five novel glucosylceramide synthase (UDP-glucose:ceramide glucosyltrans ferase) genes were identified from the plant Gossypium arboreum (cotton), t he nematode Caenorhabditis elegans, and the fungi Magnaporthe grisea, Candi da albicans, and P. pastoris. The glycosyltransferase gene expressions led to the biosynthesis of different molecular species of glucosylceramides tha t contained either C18 or very long chain fatty acids. The latter are usual ly channeled exclusively into inositol-containing sphingolipids known from Saccharomyces cerevisiae and other yeasts. Implications for the biosynthesi s, transport, and function of sphingolipids will be discussed.