title: Perturbation of ATP-induced tetramerization of human cytosolic thymidine kinase by substitution of serine-13 with aspartic acid at the mitotic phosphorylation site.
abstract: Human cytosolic thymidine kinase (TK1) is tightly regulated in the cell cycle by multiple mechanisms. Our laboratory has previously shown that in mitotic-arrested cells human TK1 is phosphorylated at serine-13, accompanied by a decrease in catalytic efficiency. In this study we investigated whether serine-13 phosphorylation regulated TK1 activity and found that substitution of serine-13 with aspartic acid (S13D), which mimics phosphorylation, not only diminished the ATP-activating effect on the enzyme, but also decreased its thymidine substrate affinity. Our experimental results further showed that the S13D mutation perturbed ATP-induced tetramerization of TK1. Given that the dimeric form of TK1 is less active than the tetrameric, we propose that mitotic phosphorylation of serine-13 is of physiological importance, in that it may counteract ATP-dependent activation of TK1 by affecting its quaternary structure, thus attenuating its enzymatic function at the G2/M phase.
authors.affiliation: Institute of Biochemistry and Molecular Biology, College of Medicine, National Taiwan University, No 1 Jen Ai Road First Section, Taipei, Taiwan ROC.
authors.forename: Chia-Lung
authors.initials: CL
authors.lastname: Li
authors.forename: Ching-Yi
authors.initials: CY
authors.lastname: Lu
authors.forename: Po-Yuan
authors.initials: PY
authors.lastname: Ke
authors.forename: Zee-Fen
authors.initials: ZF
authors.lastname: Chang
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry* / Q000494:pharmacology; D001224:Aspartic Acid / Q000737:chemistry; D002384:Catalysis; D002453:Cell Cycle; D002460:Cell Line; D002845:Chromatography; D002850:Chromatography, Gel; D003600:Cytosol / Q000201:enzymology*; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D016195:G2 Phase; D006801:Humans; D007700:Kinetics; D008938:Mitosis; D008954:Models, Biological; D009154:Mutation; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D020836:Protein Structure, Quaternary; D012694:Serine / Q000737:chemistry*; D013936:Thymidine / Q000494:pharmacology; D013937:Thymidine Kinase / Q000737:chemistry*
chemical_list: D001224:Aspartic Acid; D012694:Serine; D000255:Adenosine Triphosphate; D013937:Thymidine Kinase; C092717:thymidine kinase 1; D013936:Thymidine