Structural and Functional Analysis of a Glycosphingolipid from the Opportunistic Yeast Candida albicans.
Chantal Fradin, Courjol Flavie, Devillers Audrey and Thierry Jouault
Inserm Unit 995 team 2, University of Lille2
Lille, France

	Recent studies have highlighted the role of glycolipids, including sphingolipids, in the development of fungi and fungal-induced pathogenesis. In the yeast Candida albicans, a prominent opportunistic fungal pathogen in developed countries, we have characterized a glycosphingolipid (GSL) from the mannosyl-inositol phosphorylceramide (MIPC) family named phopholipomannan (PLM). This GSL is present at the cell wall and is shed in contact with host cells. The glycan moiety of PLM is composed of β-1,2 mannosides whose degrees of polymerization vary according to the strains serotype: up to 19 and 9 for C. albicans serotypes A and B, respectively. Biosynthesis of β- mannosides involves two β-1,2 mannosyltrasferases (Bmts) that initiate (Bmt5) and elongate (Bmt6) the glycan chains. Using different bmts∆ mutants, we first analyzed PLM β- mannosylation and its location inside C. albicans cell wall. β- mannosides addition to PLM may favor its transfer from the plasma membrane to the lower layer of the cell wall. Bmt2 which is involved in the initiation of β- mannosylation of phosphomannan, can overtake Bmt5 activity and thus initiates β- mannosylation of PLM from bmt5∆ mutant. In contrast, Bmt6 activity is not compensated in bmt6∆ mutant, which expresses a PLM with short truncated oligomannosidic chain. We then compared the immuno-regulatory activities of PLMs purified from C. albicans serotype A (PLM-A), C. albicans serotype B (PLM-B) and from bmt6∆ mutant. PLMs activate caspase-1 in murine macrophage cell line J774 whatever the glycan chain length although IL-1β secretion is more intense with long glycan chain. PLMs do not stimulate ROS production, indicating that caspase-1 activation may occur through a ROS-independent pathway. In contrast, PLM presenting oligomannosides with long-chain (PLM-A) but not PLM-B nor PLM from bmt6∆, is able to induce TNF-α production in macrophages which is potentiated by Galectin-3, a lectin specific for β-Mannosides.