Divergence of catalytic mechanism within a glycosidase family provides insight into evolution of carbohydrate metabolism by human gut flora

Chem Biol. 2008 Oct 20;15(10):1058-67. doi: 10.1016/j.chembiol.2008.09.005. Epub 2008 Oct 9.


Enzymatic cleavage of the glycosidic bond yields products in which the anomeric configuration is either retained or inverted. Each mechanism reflects the dispositions of the enzyme functional groups; a facet of which is essentially conserved in 113 glycoside hydrolase (GH) families. We show that family GH97 has diverged significantly, as it contains both inverting and retaining alpha-glycosidases. This reflects evolution of the active center; a glutamate acts as a general base in inverting members, exemplified by Bacteroides thetaiotaomicron alpha-glucosidase BtGH97a, whereas an aspartate likely acts as a nucleophile in retaining members. The structure of BtGH97a and its complexes with inhibitors, coupled to kinetic analysis of active-site variants, reveals an unusual calcium ion dependence. 1H NMR analysis shows an inversion mechanism for BtGH97a, whereas another GH97 enzyme from B. thetaiotaomicron, BtGH97b, functions as a retaining alpha-galactosidase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacteroides / enzymology
  • Bacteroides / genetics
  • Biocatalysis
  • Carbohydrate Metabolism
  • Catalytic Domain
  • Enzyme Inhibitors / pharmacology
  • Evolution, Molecular*
  • Glycoside Hydrolases / antagonists & inhibitors
  • Glycoside Hydrolases / chemistry
  • Glycoside Hydrolases / metabolism*
  • Humans
  • Intestinal Mucosa / metabolism*
  • Intestines / microbiology*
  • Kinetics
  • Magnetic Resonance Spectroscopy
  • Models, Molecular
  • Protein Structure, Tertiary
  • Sequence Analysis
  • Stereoisomerism


  • Enzyme Inhibitors
  • Glycoside Hydrolases

Associated data

  • PDB/2JKA
  • PDB/2JKE
  • PDB/2JKP