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Exploration of strategies for mechanism-based inhibitor design for family GH99 endo-α-1,2-mannanases

DOI: 10.1002/chem.201800435 DOI Help

Authors: Pearl Z. Fernandes (University of Melbourne) , Marija Petricevic (University of Melbourne) , Lukasz Sobala (University of Melbourne) , Gideon J. Davies (University of York) , Spencer John Williams (University of Melbourne)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry - A European Journal

State: Published (Approved)
Published: March 2018
Diamond Proposal Number(s): 13587

Abstract: Endo‐α‐1,2‐mannosidases and ‐mannanases, members of glycoside hydrolase family 99 (GH99), cleave α‐Glc/Man‐1,3‐α‐Man‐OR structures within mammalian N‐linked glycans and fungal α‐mannan, respectively. They are proposed to act through a two‐step mechanism involving a 1,2‐anhydrosugar 'epoxide' intermediate, involving two conserved catalytic residues. In the first step Glu333 acts as general base to deprotonate the 2‐hydroxyl group adjacent to the fissile glycosidic bond, while Glu336 provides general acid assistance to departure of the aglycon. We report the synthesis of two inhibitors designed to interact with either the general base (α‐mannosyl‐1,3‐(2‐aminodeoxymannojirimycin); Man2NH2DMJ) or the general acid (α‐mannosyl‐1,3‐mannoimidazole; ManManIm). Modest affinities were observed for an endo‐α‐1,2‐mannanase from Bacteroides thetaiotaomicron. Structural studies reveal that Man2NH2DMJ binds like other iminosugar inhibitors, suggesting that the poor inhibition by this compound is not a result of a failure to achieve the expected interaction with the general base, but rather the reduction in basicity of the endocyclic nitrogen caused by introduction of a vicinal, protonated amine at C2. ManManIm binds with the imidazole headgroup distorted downwards, a result of an unfavourable interaction with a conserved active site tyrosine. This study identifies important limitations associated with mechanism‐inspired inhibitor design for GH99 enzymes.

Journal Keywords: glycosidase; X-ray crystallography; enzymes; inhibitors

Subject Areas: Biology and Bio-materials, Chemistry

Instruments: I04-Macromolecular Crystallography

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