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Related Experiment Videos

Purine nucleoside phosphorylase. 1. Structure-function studies

M D Erion1, K Takabayashi, H B Smith

  • 1Central Research Laboratory, Ciba-Geigy Ltd., Basel, Switzerland. mark.erion@gensia.com

Biochemistry
|October 8, 1997
PubMed
Summary
This summary is machine-generated.

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Investigating human purine nucleoside phosphorylase (PNP) with active-site mutants revealed Asn243 is crucial for catalysis. This residue stabilizes the transition state through hydrogen bonding, essential for enzyme activity.

Area of Science:

  • Biochemistry
  • Enzymology
  • Structural Biology

Background:

  • Human purine nucleoside phosphorylase (PNP) is a key enzyme in purine metabolism.
  • Understanding its catalytic mechanism is crucial for therapeutic target identification.
  • Previous structural data suggested potential catalytic roles for active-site residues.

Purpose of the Study:

  • To elucidate the catalytic mechanism of human purine nucleoside phosphorylase (PNP).
  • To identify key active-site residues involved in PNP catalysis through mutagenesis.
  • To characterize the kinetic parameters of PNP active-site mutants.

Main Methods:

  • Construction and characterization of 13 active-site mutants of human PNP.
  • Determination of kinetic parameters using steady-state kinetics and microtiter plate assays.

Related Experiment Videos

  • Analysis of mutant enzyme activity in phosphorolytic and synthetic reactions.

    • Main Results:

    • Mutations in the purine binding site significantly impacted enzymatic activity; Asn243Ala showed a 1000-fold decrease in kcat.
    • Asn243 likely stabilizes the transition state via hydrogen bond donation to the purine base N7, analogous to serine protease oxyanion holes.
    • His86 and Glu89 in the phosphate binding site were also important, with His86Ala and Glu89Ala mutants showing 10-25 fold reductions in activity.

    Conclusions:

    • Asn243 plays a critical role in human PNP catalysis by stabilizing the transition state.
    • His86 and Glu89 are important residues in the phosphate binding site, contributing to catalytic efficiency.
    • These findings provide a foundation for further mechanistic studies and substrate specificity investigations of PNP.