Affinage · Plasmodium

TMK

PF3D7_1251300 · thymidylate kinase

Annotated
2026-09-08
15 papers in source corpus 8 papers cited in narrative 8 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PF3D7_1251300 (TMK) is the Plasmodium falciparum thymidylate kinase, a homodimeric enzyme that phosphorylates dTMP to the diphosphate and, uniquely among thymidylate kinases, also accepts the bulkier purine substrates dGMP, GMP, and dIMP with affinity comparable to that for TMP (PMID:18477629). Crystallographic and thermodynamic analyses show a broader active-site architecture than the human enzyme: enthalpic forces govern binding of both TMP and dGMP, TMP forms additional interactions that dGMP lacks, and the active-site residues Y107 and A111 are critical for catalysis and substrate discrimination, with Y107F disproportionately impairing dGMP over TMP turnover (PMID:19126267, PMID:20353400). TMP and dGMP occupy overlapping but distinct sites in which TMP binds more tightly and cannot be displaced by dGMP, and dGMP binding to the homodimer proceeds by a half-site negative-cooperativity mechanism with heightened dimer-interface dynamics (PMID:21212540, PMID:31934749). Because the parasite lacks a pyrimidine nucleoside kinase, TMK is the entry point for activating nucleoside-analogue prodrugs, and a P-loop/lid geometry that avoids steric conflict with the azide group allows it to efficiently phosphorylate AZT-MP, positioning it as an antimalarial drug target (PMID:20353400, PMID:20833052). Structural and mutagenesis work on thymidine-urea inhibitors established that their antiparasitic activity arises predominantly from an off-target effect rather than direct TMK inhibition (PMID:23240776, PMID:29684273).

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 2008 Medium

    Establishing that the recombinant parasite enzyme is a homodimeric thymidylate kinase with an unusually broad substrate range answered whether P. falciparum TMK differs functionally from canonical thymidylate kinases.

    Evidence Heterologous expression in E. coli with steady-state kinetics on TMP, dUMP, dGMP, GMP, and dIMP

    PMID:18477629

    Open questions at the time
    • Physiological relevance of purine-monophosphate phosphorylation in the parasite not established
    • No structural basis for broad specificity at this stage
  2. 2009 Medium

    Mutagenesis and calorimetry defined which active-site residues drive catalysis and how the enzyme energetically accommodates two chemically distinct substrates.

    Evidence Site-directed mutagenesis (Y107F, A111K) plus ITC and kinetic assays on TMP and dGMP

    PMID:19126267

    Open questions at the time
    • Full residue map of the dGMP-specificity determinants not resolved
    • Kinetic mechanism of catalysis not defined
  3. 2010 High

    Crystal structures explained the structural basis for both broad substrate acceptance and efficient AZT-MP phosphorylation, framing the enzyme as a rationally targetable drug-activation node.

    Evidence X-ray structures of ternary (dTMP-ADP, AZT-MP-ADP) and binary AP5dT complexes with kinetic interpretation

    PMID:20353400 PMID:20833052

    Open questions at the time
    • In vivo essentiality of TMK not tested genetically
    • Prodrug activation shown biochemically and in cell assays but not validated in animal infection
  4. 2011 Medium

    Competition binding resolved how TMP and dGMP share the active site, showing TMP is the preferred, more tightly bound ligand.

    Evidence ITC competition binding experiments with TMP and dGMP

    PMID:21212540

    Open questions at the time
    • Consequence of substrate competition for nucleotide-pool homeostasis in the parasite unknown
  5. 2018 Medium

    Combined structural, mutagenesis, and affinity work with thymidine-urea inhibitors clarified that their antiparasitic activity is largely off-target, an important caution for TMK-directed drug discovery.

    Evidence Enzyme-inhibitor crystal structures, mutagenesis, Ki/KD determination, docking, and parasite growth assays

    PMID:23240776 PMID:29684273

    Open questions at the time
    • The actual off-target(s) responsible for growth inhibition not identified
    • No validated on-target TMK inhibitor established
  6. 2020 High

    Dynamic and thermodynamic profiling revealed a half-site negative-cooperativity mechanism for dGMP binding, explaining how the homodimer manages purine substrate handling.

    Evidence ITC, tryptophan fluorescence, NMR relaxation dispersion, molecular mechanics, and mutagenesis on the PfTMK dimer

    PMID:31934749

    Open questions at the time
    • Functional/biological significance of half-site behavior in the parasite unknown
    • Whether negative cooperativity also governs the physiological TMP reaction not resolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • Whether TMK is genetically essential in P. falciparum and can be selectively targeted in vivo remains unresolved.
  • No genetic knockout/knockdown data in the corpus
  • No validated on-target inhibitor with in vivo efficacy
  • In vivo prodrug-activation role not confirmed

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Complex memberships
Homodimer

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2008 Recombinant P. falciparum TMK (PfTMK) expressed in E. coli is a homodimer that phosphorylates dTMP and dUMP and, uniquely among thymidylate kinases, also accepts bulkier purine substrates dGMP, GMP, and dIMP. Km values for TMP and dGMP are 22 and 30 µM respectively; kcat for TMP is 3.4 s⁻¹. The enzyme shows maximal activity over pH 7–9 and marked thermostability. Heterologous expression in E. coli, steady-state kinetic analysis, initial velocity studies Journal of biochemistry Medium 18477629
2009 Active-site mutagenesis of P. falciparum TMK showed that the A111K substitution markedly reduced kinase activity, and the Y107F mutation abolished the hydroxyl group contact required for catalysis, with a more severe impact on dGMP kinase activity than on TMP kinase activity. Thermodynamic (ITC) analysis revealed that enthalpic forces govern binding of both TMP and dGMP, with comparable overall binding affinities but lower heat produced for dGMP, indicating additional interactions occur with TMP that are lost with the larger purine substrate. Site-directed mutagenesis, isothermal titration calorimetry (ITC), kinetic assays Parasitology Medium 19126267
2010 Crystal structures of P. falciparum TMK in ternary complexes (dTMP-ADP and AZT-MP-ADP) and a binary complex with transition-state analogue AP5dT revealed the structural basis for efficient phosphorylation of AZT-MP: the P-loop and lid region adopt a conformation in which the azide of AZT-MP faces no steric conflicts, requiring no further P-loop movement to reach the transition state, in contrast to the human enzyme. These structures also explain the unique ability to accept dGMP as a substrate through a broader active-site architecture compared with human TMPK. X-ray crystallography (ternary and binary complexes), kinetic analysis The Biochemical journal High 20353400
2010 P. falciparum TMK efficiently phosphorylates AZT-MP (kinetics comparable to the E. coli type II enzyme) and can activate prodrug analogues of AZT at the monophosphate level. The parasite lacks a pyrimidine nucleoside kinase, so TMK serves as the entry point for nucleoside analogue activation to the monophosphate in the de novo pyrimidine pathway. Enzyme kinetics with recombinant PfTMK, prodrug cell-based antiparasitic assays Bioorganic & medicinal chemistry Medium 20833052
2011 ITC competition binding experiments showed that dGMP cannot displace TMP from the PfTMK active site, whereas TMP can partially displace dGMP with reduced affinity, indicating that TMP and dGMP share overlapping but distinct binding sites with TMP binding more tightly and exhibiting higher enthalpic interactions. Isothermal titration calorimetry (ITC) competition binding Biological & pharmaceutical bulletin Medium 21212540
2012 Crystal structures of PfTMK in complex with α- and β-thymidine urea-derivative inhibitors were solved, revealing the structural basis for inhibitor binding and demonstrating that certain 5'-urea-α-thymidine analogues inhibit parasite growth primarily through an off-target mechanism rather than PfTMK inhibition. X-ray crystallography of enzyme-inhibitor complexes, enzymatic inhibition assays, parasite growth assays Journal of medicinal chemistry Medium 23240776
2018 Mutagenesis combined with docking simulations mapped the binding site of α-thymidine urea-derivative inhibitors on PfTMK. Measured Ki and KD values for these compounds were significantly weaker than their reported EC50 for parasite growth inhibition, indicating that parasite growth inhibition by these compounds is predominantly due to an off-target effect rather than PfTMK inhibition. Site-directed mutagenesis, enzyme inhibition assays (Ki determination), binding affinity measurement (KD), molecular docking Biochemistry Medium 29684273
2020 NMR relaxation dispersion and ITC studies showed that dGMP binding to the PfTMK homodimer exhibits a unique half-site binding mechanism (negative cooperativity), with the second protomer's active site occluded after initial dGMP binding. The dGMP-enzyme complex is more conformationally dynamic at the dimer interface than the TMP-enzyme complex on the µs–ms timescale. Mutational studies identified residues contributing to the unique capacity to utilize dGMP as a substrate. Isothermal titration calorimetry, tryptophan fluorescence titration, NMR relaxation dispersion, molecular mechanics calculations, site-directed mutagenesis Biochemistry High 31934749

Source papers

Stage 0 corpus · 15 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2010 Structural basis for the efficient phosphorylation of AZT-MP (3'-azido-3'-deoxythymidine monophosphate) and dGMP by Plasmodium falciparum type I thymidylate kinase. The Biochemical journal 34 20353400
2012 Synthesis and evaluation of α-thymidine analogues as novel antimalarials. Journal of medicinal chemistry 30 23240776
2009 Mutational, inhibitory and microcalorimetric analyses of Plasmodium falciparum TMP kinase. Implications for drug discovery. Parasitology 29 19126267
2008 Molecular characterization, heterologous expression and kinetic analysis of recombinant Plasmodium falciparum thymidylate kinase. Journal of biochemistry 23 18477629
2010 Potential application of thymidylate kinase in nucleoside analogue activation in Plasmodium falciparum. Bioorganic & medicinal chemistry 14 20833052
2023 Structure-based virtual screening against multiple Plasmodium falciparum kinases reveals antimalarial compounds. Molecular diversity 11 38127294
2013 First report on exploring structural requirements of α and β thymidine analogs for PfTMPK inhibitory activity using in silico studies. Bio Systems 11 23850534
2009 The exceptional properties of Plasmodium deoxyguanylate pathways as a potential area for metabolic and drug discovery studies. Nucleic acids symposium series (2004) 11 19749249
2012 Carbocyclic thymidine derivatives efficiently inhibit Plasmodium falciparum thymidylate kinase (PfTMK). Parasitology international 9 22425904
2011 The substrate binding preferences of Plasmodium thymidylate kinase. Biological & pharmaceutical bulletin 9 21212540
2009 Thymidylate kinase: the lost chemotherapeutic target. Nucleic acids symposium series (2004) 9 19749371
2013 Synthesis of carbocyclic pyrimidine nucleosides and their inhibitory activities against Plasmodium falciparum thymidylate kinase. Parasitology international 8 23583697
2018 Interaction of α-Thymidine Inhibitors with Thymidylate Kinase from Plasmodium falciparum. Biochemistry 6 29684273
2019 The structural basis of unique substrate recognition by Plasmodium thymidylate kinase: Molecular dynamics simulation and inhibitory studies. PloS one 5 30730992
2020 dGMP Binding to Thymidylate Kinase from Plasmodium falciparum Shows Half-Site Binding and Induces Protein Dynamics at the Dimer Interface. Biochemistry 3 31934749