Structure and Catalytic Mechanism of Glucosamine 6-phosphate Deaminase From Escherichia Coli at 2.1 A Resolution

Structure. 1995 Dec 15;3(12):1323-32. doi: 10.1016/s0969-2126(01)00270-2.

Abstract

Background: Glucosamine 6-phosphate deaminase from Escherichia coli is an allosteric hexameric enzyme which catalyzes the reversible conversion of D-glucosamine 6-phosphate into D-fructose 6-phosphate and ammonium ion and is activated by N-acetyl-D-glucosamine 6-phosphate. Mechanistically, it belongs to the group of aldoseketose isomerases, but its reaction also accomplishes a simultaneous amination/deamination. The determination of the structure of this protein provides fundamental knowledge for understanding its mode of action and the nature of allosteric conformational changes that regulate its function.

Results: The crystal structure of glucosamine 6-phosphate deaminase with bound phosphate ions is presented at 2.1 A resolution together with the refined structures of the enzyme in complexes with its allosteric activator and with a competitive inhibitor. The protein fold can be described as a modified NAD-binding domain.

Conclusions: From the similarities between the three presented structures, it is concluded that these represent the enzymatically active R state conformer. A mechanism for the deaminase reaction is proposed. It comprises steps to open the pyranose ring of the substrate and a sequence of general base-catalyzed reactions to bring about isomerization and deamination, with Asp72 playing a key role as a proton exchanger.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aldose-Ketose Isomerases*
  • Allosteric Regulation
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Binding Sites
  • Carbohydrate Epimerases / antagonists & inhibitors
  • Carbohydrate Epimerases / chemistry*
  • Carbohydrate Epimerases / metabolism
  • Catalysis
  • Crystallography, X-Ray
  • Enzyme Inhibitors / pharmacology
  • Escherichia coli / enzymology*
  • Fructosephosphates / biosynthesis
  • Glucosamine / analogs & derivatives
  • Glucosamine / metabolism
  • Glucose-6-Phosphate* / analogs & derivatives*
  • Glucosephosphates / metabolism
  • Macromolecular Substances
  • Models, Molecular*
  • NAD / metabolism
  • Phosphates / metabolism
  • Protein Conformation*
  • Sorbitol / analogs & derivatives
  • Sorbitol / chemistry
  • Sorbitol / pharmacology
  • Sugar Phosphates / chemistry
  • Sugar Phosphates / pharmacology

Substances

  • 2-deoxy-2-aminoglucitol-6-phosphate
  • Bacterial Proteins
  • Enzyme Inhibitors
  • Fructosephosphates
  • Glucosephosphates
  • Macromolecular Substances
  • Phosphates
  • Sugar Phosphates
  • NAD
  • glucosamine 6-phosphate
  • Sorbitol
  • Glucose-6-Phosphate
  • fructose-6-phosphate
  • glucosamine-6-phosphate isomerase
  • Carbohydrate Epimerases
  • Aldose-Ketose Isomerases
  • Glucosamine