Candida albicans β-1,2 mannosyl transferase Bmt3: Preparation and evaluation of a β (1,2), α (1,2)-tetramannosyl fluorescent substrate

We describe for the first time the chemical synthesis of a tetramannoside, containing both α (1→2) and β (1→2) linkages. Dodecylthio (lauryl) glycosides were prepared from odorless dodecyl thiol and used as donors for the glycosylation steps. This tetramannoside, was coupled to a mantyl group, and revealed to be a perfect substrate of β-mannosyltransferase Bmt3, confirming the proposed specificity and allowing the preparation of a pentamannoside sequence (β Man (1,2) β Man (1,2) α Man (1,2) α Man (1,2) α Man) usable as a novel substrate for further elongation studies.

Evaluation of monovalent and multivalent iminosugars to modulate Candida albicans β-1,2-mannosyltransferase activities

β-1,2-Linked oligomannosides substitute the cell wall of numerous yeast species. Several of those including Candida albicans may cause severe infections associated with high rates of morbidity and mortality, especially in immunocompromised patients. β-1,2-Mannosides are known to be involved in the pathogenic process and to elicit an immune response from the host. In C. albicans, the synthesis of β-mannosides is under the control of a family of nine genes coding for putative β-mannosyltransferases. Two of them, CaBmt1 and CaBmt3, have been shown to initiate and prime the elongation of the β-mannosides on the cell-wall mannan core. In the present study, we have assessed the modulating activities of monovalent and multivalent iminosugar analogs on these enzymes in order to control the enzymatic bio-synthesis of β-mannosides. We have identified a monovalent deoxynojirimycin (DNJ) derivative that inhibits the CaBmt1-catalyzed initiating activity, and mono-, tetra- and polyvalent deoxymannojirimycin (DMJ) that modulate the CaBmt1 activity toward the formation of a single major product. Analysis of the aggregating properties of the multivalent iminosugars showed their ability to elicit clusterization of both CaBmt1 and CaBmt3, without affecting their activity. These results suggest promising roles for multivalent iminosugars as controlling agents for the biosynthesis of β-1,2 mannosides and for monovalent DNJ derivative as a first target for the design of future β-mannosyltransferase inhibitors.

Rapid and efficient synthesis of α(1–2)mannobiosides

A very rapid, versatile and high yield synthesis of Manα1,2Man derivatives using a common orthogonal benzoyl/acetyl protection strategy compatible with the presence of azido groups and the use of CuAAC for conjugating the α(1–2)mannobiosides to different scaffolds, reducing the cost and time of the synthesis and improving the overall yield.

Candida albicans β-1,2-mannosyltransferase Bmt3 prompts the elongation of the cell-wall phosphopeptidomannan

β-1,2-Linked mannosides are expressed on numerous cell-wall glycoconjugates of the opportunistic pathogen yeast Candida albicans. Several studies evidenced their implication in the host-pathogen interaction and virulence mechanisms. In the present study, we characterized the in vitro activity of CaBmt3, a β-1,2-mannosyltransferase involved in the elongation of β-1,2-oligomannosides oligomers onto the cell-wall polymannosylated N-glycans. A recombinant soluble enzyme Bmt3p was produced in Pichia pastoris and its enzyme activity was investigated using natural and synthetic oligomannosides as potential acceptor substrates. Bmt3p was shown to exhibit an exquisite enzymatic specificity by adding a single terminal β-mannosyl residue to α-1,2-linked oligomannosides capped by a Manβ1-2Man motif. Furthermore, we demonstrated that the previously identified CaBmt1 and CaBmt3 efficiently act together to generate Manβ1-2Manβ1-2[Manα1-2]n sequence from α-1,2-linked oligomannosides onto exogenous and endogenous substrates.

Characterization of the recombinant Candida albicans β-1,2-mannosyltransferase that initiates the β-mannosylation of cell wall phosphopeptidomannan

The presence of β-mannosides in their cell walls confers specific features on the pathogenic yeasts Candida albicans and Candida glabrata compared with non-pathogenic yeasts. In the present study, we investigated the enzymatic properties of Bmt1 (β-mannosyltransferase 1), a member of the recently identified β-mannosyltransferase family, from C. albicans. 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 Saccharomyces 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 consecuti-vely transfers two mannosyl units on to these acceptors, leading to the production of α-mannosidase-resistant oligomannosides. NMR experiments further confirmed the presence of a terminal βMan (β-1,2-linked mannose) unit in the first enzyme product. In the future, a better understanding of specific β-1,2-mannosyltransferase molecular requirements will help the design of new potential antifungal drugs.