Evolution of Metamorphism in Thymidylate Synthases Within the Primate Lineages |
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Authors: | BeiBei?Luo Saphronia?R?Johnson Lukasz?Lebioda Email author" target="_blank">Sondra?H?BergerEmail author |
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Institution: | (1) Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, 700 Sumter Street, Columbia, SC 29208, USA;(2) Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA; |
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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 (k
cat) of mutant enzymes were 45–149% of hTS, with the lysine mutant (R163K) exhibiting the highest k
cat. 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 (K
d) 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. |
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