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Human thymidylate synthase is in the closed conformation when complexed with dUMP and raltitrexed, an antifolate drug

J Phan1, S Koli, W Minor

  • 1Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 92908, USA.

Biochemistry
|May 1, 2001
PubMed

Insights

Structural analysis reveals how the antifolate drug raltitrexed inhibits thymidylate synthase (TS) in colorectal cancer. The enzyme adopts a closed conformation, forming a covalent bond with the drug for effective cancer chemotherapy.

Area of Science:

  • Biochemistry
  • Structural Biology
  • Cancer Research

Background:

  • Thymidylate synthase (TS) is a critical target in chemotherapy for colorectal cancer and other neoplasms.
  • Raltitrexed (Tomudex) is an antifolate inhibitor of TS used clinically in Europe.

Purpose of the Study:

  • To determine the crystal structure of the complex formed between recombinant human TS, dUMP, and raltitrexed.
  • To elucidate the molecular interactions and binding mode of raltitrexed to human TS.

Main Methods:

  • X-ray crystallography was employed to determine the structure at 1.9 Å resolution.
  • Analysis of the enzyme-inhibitor complex structure.

Main Results:

  • The human TS enzyme adopts a closed conformation upon binding dUMP and raltitrexed.
  • A covalent bond is formed between the catalytic Cys 195 and dUMP in both enzyme subunits.
  • Key differences from rat TS include a direct hydrogen bond between His 196 and dUMP's O4 atom and repositioning of Tyr 94.
  • The drug's thiophene ring exhibits disorder, occupying two parallel positions.

Conclusions:

  • The determined structure provides detailed insights into the mechanism of raltitrexed inhibition of human TS.
  • This understanding can inform the development of novel TS inhibitors for cancer therapy.

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