Characterization of the recombinant Candida albicans β-1,2 mannosyltransferase that initiates the β-mannosylation of cell-wall phosphopeptidomannan.
Résumé
: Substitution of cell-wall components by β-mannosides confers to the pathogenic yeasts Candida albicans and C. glabrata specific features compared to non pathogenic yeasts. Here, we investigated the enzymatic properties of Bmt1 from C. albicans, a member of the recently identified β-mannosyltransferase family. A recombinant soluble enzyme lacking the N-terminal region was expressed as a secreted protein from the methylotrophic yeast Pichia pastoris. In parallel, functionalized natural oligosaccharides isolated from S. cerevisiae and a C. albicans mutant strain as well as synthetic α-oligomannosides were prepared and used as potential acceptor substrates. Bmt1p preferentially utilizes substrates containing linear chains of α-1,2 linked mannotriose or mannotetraose. The recombinant enzyme consecutively transfers two mannosyl units onto these acceptors, leading to the production of α-mannosidase resistant oligomannosides. NMR experiments further confirmed the presence of terminal β-1,2-linked mannose unit in the first enzyme product. In the future, a better understanding of specific β-1,2 mannosyltransferases molecular requirements would orient the design of new potential antifungal drugs.