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Crystal structure of Saccharomyces cerevisiae Mnn9 in complex with GDP and Mn.
Structural highlights
FunctionMNN9_YEAST The M-Pol I and M-Pol II complexes possess alpha-1,6-mannosyltransferase activity and are probably involved in the elongation of the mannan backbone of N-linked glycans on cell wall and periplasmic proteins. May also provide alpha-1,2-mannosyltransferase activity to the M-Pol I complex.[1] Publication Abstract from PubMedThe 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' alpha-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 alpha-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. Yeast Mnn9 is both a priming glycosyltransferase and an allosteric activator of mannan biosynthesis.,Striebeck A, Robinson DA, Schuttelkopf AW, van Aalten DM Open Biol. 2013 Sep 11;3(9):130022. doi: 10.1098/rsob.130022. PMID:24026536[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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