Journal of Molecular Evolution

, Volume 72, Issue 3, pp 306–314

Evolution of Metamorphism in Thymidylate Synthases Within the Primate Lineages

  • BeiBei Luo
  • Saphronia R. Johnson
  • Lukasz Lebioda
  • Sondra H. Berger
Article

DOI: 10.1007/s00239-011-9433-8

Cite this article as:
Luo, B., Johnson, S.R., Lebioda, L. et al. J Mol Evol (2011) 72: 306. doi:10.1007/s00239-011-9433-8

Abstract

Crystal structures of human thymidylate synthase (hTS) revealed that the protein exists in active and inactive conformations, defined by the position of a loop containing the active site nucleophile. TS is highly homologous among diverse species; however, the residue at position 163 (hTS) differs among species. Arginine at this position is predicted by structural modeling to enable conformational switching. Arginine or lysine is reported at this position in all mammals in the GenBank and Ensembl databases, with arginine reported in only primates. Sequence analysis of the TS gene of representative primates revealed that arginine occurs at this relative position in all primates except a representative of prosimians. Mutant human proteins were created with residues at position 163 that occur in TSs from prokaryotes and eukaryotes. Catalytic constants (kcat) of mutant enzymes were 45–149% of hTS, with the lysine mutant (R163K) exhibiting the highest kcat. The effect of lysine substitution on solution structure and on ligand binding was investigated. R163K exhibited higher intrinsic fluorescence, a more negative molar ellipticity, and higher dissociation constants (Kd) for ligands that modulate protein conformation than hTS. Temperature effects on intrinsic fluorescence and catalytic activity of hTS and R163K are consistent with proteins populating different conformational states. The data indicate that the enzyme with arginine at the position corresponding to 163 (hTS) evolved after the divergence of prosimians and simians and that substitution of lysine by arginine confers unique structural and functional properties to the enzyme expressed in simian primates.

Keywords

Protein metamorphismEnzyme catalysisPrimate evolutionIntrinsic fluorescenceConformational switchingProtein structureEnergy of activation

Abbreviations

TS

Thymidylate synthase (h, human; ec, Escherichia coli)

mTHF

5,10-Methylenetetrahydrofolate

DHF

Dihydrofolate

ZD1694

N-(5-[N-(3,4-Dihydro-2-methyl-4-oxyquinazolin-6-ylmethyl)-N-methyl-amino]-2-thenoyl)-l-glutamic acid (raltitrexed, Tomudex)

CD

Circular dichroism

Supplementary material

239_2011_9433_MOESM1_ESM.pdf (212 kb)
Supplementary material 1 (PDF 211 kb)

Copyright information

© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  • BeiBei Luo
    • 1
  • Saphronia R. Johnson
    • 1
  • Lukasz Lebioda
    • 2
  • Sondra H. Berger
    • 1
  1. 1.Department of Pharmaceutical and Biomedical Sciences, South Carolina College of PharmacyUniversity of South CarolinaColumbiaUSA
  2. 2.Department of Chemistry and BiochemistryUniversity of South CarolinaColumbiaUSA