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A Novel Saturation Mutagenesis Approach: Single Step Characterization of Regulatory Protein Binding Sites in RNA Using Phosphorothioates
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A Novel Saturation Mutagenesis Approach: Single Step Characterization of Regulatory Protein Binding Sites in RNA Using Phosphorothioates

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Design and characterization of a mutation outside the active site of human thymidylate synthase that affects ligand

D Cardinale1, O M H Salo-Ahen, G Guaitoli

  • 1Dipartimento di Scienze Farmaceutiche, Università degli Studi di Modena e Reggio Emilia, Via Campi 183, 41100Modena, Italy.

Protein Engineering, Design & Selection : PEDS
|December 4, 2009
PubMed

Insights

A mutation in human thymidylate synthase (hTS) created a resistant enzyme. This finding reveals how A-helix changes can impact drug resistance in cancer therapy.

Area of Science:

  • Biochemistry and Molecular Biology
  • Enzymology
  • Cancer Therapeutics

Background:

  • Human thymidylate synthase (hTS) is a key enzyme in DNA synthesis and a target for cancer drugs like fluoropyrimidines.
  • Drug resistance and toxicity limit the clinical efficacy of hTS inhibitors.

Purpose of the Study:

  • To investigate the structural role of the A-helix in fluoropyrimidine resistance.
  • To understand the mechanism of drug resistance through enzyme mutation.

Main Methods:

  • Created a single point mutation (Glu30Trp) in hTS to generate a resistant mutant.
  • Assessed enzyme activity and inhibition constants (FdUMP).
  • Utilized circular dichroism for structural analysis and molecular modeling/simulation for mechanistic insights.

Main Results:

  • The Glu30Trp mutant exhibited 100-fold lower specific activity than wild-type hTS.
  • The mutant displayed a 6-fold higher inhibition constant for FdUMP, indicating resistance.
  • Circular dichroism confirmed the mutant enzyme remains folded.
  • Molecular modeling suggested altered hydrogen bonding between residue 30 and the active site causes resistance.

Conclusions:

  • The A-helix plays a significant role in modulating fluoropyrimidine resistance in hTS.
  • The Glu30Trp mutation confers resistance by disrupting the enzyme's active site through long-range effects.
  • This study provides structural insights into hTS inhibitor resistance, potentially guiding future drug development.

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