Yeast Mnn9 is both a priming glycosyltransferase and an allosteric activator of mannan biosynthesis

Alexander Striebeck, David A. Robinson, Alexander W. Schüttelkopf, Daan M. F. van Aalten

    Research output: Contribution to journalArticlepeer-review

    23 Citations (Scopus)


    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' a-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 a-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.
    Original languageEnglish
    Article number130022
    JournalOpen Biology
    Issue number9
    Publication statusPublished - Sept 2013


    • Allosteric Regulation
    • Amino Acid Sequence
    • Candida albicans
    • Crystallography, X-Ray
    • Guanosine Diphosphate
    • Mannans
    • Mannosyltransferases
    • Membrane Glycoproteins
    • Membrane Proteins
    • Models, Molecular
    • Molecular Sequence Data
    • Protein Conformation
    • Saccharomyces cerevisiae
    • Saccharomyces cerevisiae Proteins


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