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Evidence for a Boat Conformation at the Transition State of GH76 α‐1,6‐Mannanases—Key Enzymes in Bacterial and Fungal Mannoprotein Metabolism
Author(s) -
Thompson Andrew J.,
Speciale Gaetano,
IglesiasFernández Javier,
Hakki Zalihe,
Belz Tyson,
Cartmell Alan,
Spears Richard J.,
Chandler Emily,
Temple Max J.,
Stepper Judith,
Gilbert Harry J.,
Rovira Carme,
Williams Spencer J.,
Davies Gideon J.
Publication year - 2015
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201410502
Subject(s) - chemistry , enzyme , stereochemistry , biocatalysis , catalysis , biochemistry , reaction mechanism
α‐Mannosidases and α‐mannanases have attracted attention for the insight they provide into nucleophilic substitution at the hindered anomeric center of α‐mannosides, and the potential of mannosidase inhibitors as cellular probes and therapeutic agents. We report the conformational itinerary of the family GH76 α‐mannanases studied through structural analysis of the Michaelis complex and synthesis and evaluation of novel aza/imino sugar inhibitors. A Michaelis complex in an O S 2 conformation, coupled with distortion of an azasugar in an inhibitor complex to a high energy B 2,5 conformation are rationalized through ab initio QM/MM metadynamics that show how the enzyme surface restricts the conformational landscape of the substrate, rendering the B 2,5 conformation the most energetically stable on‐enzyme. We conclude that GH76 enzymes perform catalysis using an itinerary that passes through O S 2 and B 2,5 ≠ conformations, information that should inspire the development of new antifungal agents.