Open AccessReplacement set mutagenesis of the four phosphate-binding arginine residues of thymidylate synthase
Author(s) -
Shido Kawase,
SungWoo Cho,
James A Rozelle,
Rhonda M. Stroud,
J. Finer-Moore,
Daniel V. Santi
Publication year - 2000
Publication title -
protein engineering, design and selection
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.627
H-Index - 109
eISSN - 1741-0134
pISSN - 1741-0126
DOI - 10.1093/protein/13.8.557
Subject(s) - thymidylate synthase , arginine , phosphate , mutagenesis , chemistry , biochemistry , site directed mutagenesis , biology , genetics , mutation , amino acid , mutant , gene , fluorouracil , chemotherapy
Arginines R23, R178, R179 and R218 in thymidylate synthase (TS, EC 2. 1.1.45) are hydrogen bond donors to the phosphate moiety of the substrate, dUMP. In order to investigate how these arginines contribute to enzyme function, we prepared complete replacement sets of mutants at each of the four sites in Lactobacillus casei TS. Mutations of R23 increase K:(m) for dUMP 2-20-fold, increase K:(m) for cofactor 8-40-fold and decrease k(cat) 9-20-fold, reflecting the direct role of the R23 side chain in binding and orienting the cofactor in ternary complexes of the enzyme. Mutations of R178 increase K:(m) for dUMP 40-2000-fold, increase K:(m) for cofactor 3-20-fold and do not significantly affect k(cat). These results are consistent with the fact that this residue is an integral part of the dUMP-binding wall and contributes to the orientation and ordering of several other dUMP binding residues. Kinetic parameters for all R179 mutations except R179P were not significantly different from wild-type values, reflecting the fact that this external arginine does not directly contact the cofactor or other ligand-binding residues. R218 is essential for the structure of the catalytic site and all mutations of this arginine except R218K were inactive.