Download MendeleyYeast Mnn9 is Both a Priming Glycosyltransferase and an Allosteric Activator of Mannan Biosynthesis.
Striebeck, A., Robinson, D.A., Schuettelkopf, A.W., Van Aalten, D.M.F.(2013) Open Biol 3: 30022
- PubMed: 24026536
- DOI: https://doi.org/10.1098/rsob.130022
- Primary Citation of Related Structures:
3ZF8 - PubMed Abstract:
The fungal cell possesses an essential carbohydrate cell wall. The outer layer, mannan, is formed by mannoproteins carrying highly mannosylated O- and N-linked glycans. Yeast mannan biosynthesis is initiated by a Golgi-located complex (M-Pol I) of two GT-62 mannosyltransferases, Mnn9p and Van1p, that are conserved in fungal pathogens. Saccharomyces cerevisiae and Candida albicans mnn9 knockouts show an aberrant cell wall and increased antibiotic sensitivity, suggesting the enzyme is a potential drug target. Here, we present the structure of ScMnn9 in complex with GDP and Mn(2+), defining the fold and catalytic machinery of the GT-62 family. Compared with distantly related GT-78/GT-15 enzymes, ScMnn9 carries an unusual extension. Using a novel enzyme assay and site-directed mutagenesis, we identify conserved amino acids essential for ScMnn9 'priming' α-1,6-mannosyltransferase activity. Strikingly, both the presence of the ScMnn9 protein and its product, but not ScMnn9 catalytic activity, are required to activate subsequent ScVan1 processive α-1,6-mannosyltransferase activity in the M-Pol I complex. These results reveal the molecular basis of mannan synthesis and will aid development of inhibitors targeting this process.
Organizational Affiliation:
Division of Molecular Microbiology, University of Dundee, Dundee DD1 5EH, UK.
