Evidence for a boat conformation at the transition state of GH76 α-1,6-mannanases--key enzymes in bacterial and fungal mannoprotein metabolism

Angew Chem Int Ed Engl. 2015 Apr 27;54(18):5378-82. doi: 10.1002/anie.201410502. Epub 2015 Mar 13.


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) S2 conformation, coupled with distortion of an azasugar in an inhibitor complex to a high energy B2,5 conformation are rationalized through ab initio QM/MM metadynamics that show how the enzyme surface restricts the conformational landscape of the substrate, rendering the B2,5 conformation the most energetically stable on-enzyme. We conclude that GH76 enzymes perform catalysis using an itinerary that passes through (O) S2 and B2,5 (≠) conformations, information that should inspire the development of new antifungal agents.

Keywords: carbohydrates; computational chemistry; conformational analysis; enzymatic mechanisms; glycosidase inhibitors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aza Compounds / chemical synthesis
  • Aza Compounds / chemistry
  • Aza Compounds / pharmacology
  • Bacillus / enzymology*
  • Bacterial Proteins / metabolism*
  • Candida albicans / enzymology*
  • Enzyme Inhibitors / chemical synthesis*
  • Enzyme Inhibitors / chemistry
  • Enzyme Inhibitors / pharmacology
  • Fungal Proteins / metabolism*
  • Imino Sugars / chemical synthesis
  • Imino Sugars / chemistry
  • Imino Sugars / pharmacology
  • Mannosidases / antagonists & inhibitors*
  • Mannosidases / chemistry
  • Models, Molecular
  • Protein Conformation


  • Aza Compounds
  • Bacterial Proteins
  • Enzyme Inhibitors
  • Fungal Proteins
  • Imino Sugars
  • Mannosidases