Thymidine kinase 1 regulatory fine‐tuning through tetramer formation

Abstract

Thymidine kinase 1 (TK1) provides a crucial precursor, deoxythymidine monophosphate, for nucleic acid synthesis, and the activity of TK1 increases by up to 200-fold during the S-phase of cell division in humans. An important part of the regulatory checkpoints is the ATP and enzyme concentration-dependent transition of TK1 from a dimer with low catalytic efficiency to a tetramer with high catalytic efficiency. This regulatory finetuning serves as an additional control to provide a balanced pool of nucleic acid precursors in the cell. We subcloned and over-expressed 10 different TK1s, originating from widely different organisms, and characterized their kinetic and oligomerization properties. Whilst bacteria, plants and Dictyostelium only exhibited dimeric TK1, we found that all animals had a tetrameric TK1. However, a clear ATP-dependent switch between dimer and tetramer was found only in higher vertebrates and was especially pronounced in mammalian and bird TK1s. We suggest that the dimer form is the original form and that the tetramer originated in the animal lineage after the split of Dictyostelium and the lineages leading to invertebrates and vertebrates. The efficient switching mechanism was probably first established in warm-blooded animals when they separated from the rest of the vertebrates. Structured digital abstract

Role of pyrimidine salvage pathway in the maintenance of organellar and nuclear genome integrity

“…Although, many roles are conserved between plants and other eukaryotes, the regulation of plant TK1 might differ from what has been described in mammals. Indeed, the posttranslational regulation of plant TK1 has been demonstrated to be different from that of other eukaryotes (Mutahir et al, 2013).…”

Lipophilic prodrugs of nucleoside triphosphates as biochemical probes and potential antivirals

“…In the case of d4T 1 , the first phosphorylation step to yield its monophosphate form 2 catalysed by the host cell enzyme thymidine kinase (TK) is metabolism-limiting because of the rather modest affinity of d4T 1 to TK as an alternative substrate and because TK activity is S-phase-dependent 11 16 17 . However, to avoid this limitation, it is not possible to apply the charged monophosphorylated metabolite because of the high polarity and thereby extremely poor, if any, membrane permeability.…”

Cell cycle regulation and novel structural features of thymidine kinase, an essential enzyme in Trypanosoma brucei

“…All these structures have the enzyme packed as a tetramer in the crystal with similar quaternary interactions: most forming a 'closed' tetramer with no ligand in the phosphate donor site, and a smaller number with an 'open' tetramer with the site occupied by a nucleobase. The majority of TKIIs are reported to be either dimers or tetramers in solution, or an equilibrium between both (Eriksson et al, 2002;Mutahir et al, 2013). Most are highly specific, phosphorylating only dThd and deoxyuridine (dUrd), and tolerate only minor changes in the 5-position of the pyrimidine base and/or in the 3 0 -position of the 2 0 -deoxyribose sugar (Johansson and Eriksson, 1996).…”