Allosteric kinetics of the isoform 1 of human glucosamine-6-phosphate deaminase

Biochim Biophys Acta. 2011 Dec;1814(12):1846-53. doi: 10.1016/j.bbapap.2011.07.010. Epub 2011 Jul 21.

Abstract

The human genome contains two genes encoding for two isoforms of the enzyme glucosamine-6-phosphate deaminase (GNPDA, EC 3.5.99.6). Isoform 1 has been purified from several animal sources and the crystallographic structure of the human recombinant enzyme was solved at 1.75Å resolution (PDB ID: 1NE7). In spite of their great structural similarity, human and Escherichia coli GNPDAs show marked differences in their allosteric kinetics. The allosteric site ligand, N-acetylglucosamine 6-phosphate (GlcNAc6P), which is an activator of the K-type of E. coli GNPDA has an unusual mixed allosteric effect on hGNPDA1, behaving as a V activator and a K inhibitor (antiergistic or crossed mixed K(-)V(+) effect). In the absence of GlcNAc6P, the apparent k(cat) of the enzyme is so low, that GlcNAc6P behaves as an essential activator. Additionally, substrate inhibition, dependent on GlcNAc6P concentration, is observed. All these kinetic properties can be well described within the framework of the Monod allosteric model with some additional postulates. These unusual kinetic properties suggest that hGNPDA1 could be important for the maintenance of an adequate level of the pool of the UDP-GlcNAc6P, the N-acetylglucosylaminyl donor for many reactions in the cell. In this research we have also explored the possible functional significance of the C-terminal extension of hGNPDA1 enzyme, which is not present in isoform 2, by constructing and studying two mutants truncated at positions 268 and 275.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylglucosamine / analogs & derivatives
  • Acetylglucosamine / metabolism
  • Aldose-Ketose Isomerases / chemistry*
  • Aldose-Ketose Isomerases / genetics
  • Aldose-Ketose Isomerases / isolation & purification
  • Aldose-Ketose Isomerases / metabolism*
  • Allosteric Regulation / physiology*
  • Allosteric Site
  • Amino Acid Sequence
  • Binding Sites
  • Catalysis
  • Humans
  • Isoenzymes / genetics
  • Isoenzymes / metabolism
  • Kinetics
  • Models, Molecular
  • Molecular Sequence Data
  • Mutant Proteins / chemistry
  • Mutant Proteins / genetics
  • Mutant Proteins / isolation & purification
  • Mutant Proteins / metabolism
  • Protein Conformation
  • Sequence Homology, Amino Acid
  • Substrate Specificity

Substances

  • Isoenzymes
  • Mutant Proteins
  • N-acetylglucosamine 6-phosphate
  • glucosamine-6-phosphate isomerase
  • Aldose-Ketose Isomerases
  • Acetylglucosamine