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Bonin JP, Sapienza PJ, Lee AL. Dynamic allostery in substrate binding by human thymidylate synthase. eLife 2022; 11:79915. [PMID: 36200982 PMCID: PMC9536839 DOI: 10.7554/elife.79915] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2022] [Accepted: 08/31/2022] [Indexed: 11/25/2022] Open
Abstract
Human thymidylate synthase (hTS) is essential for DNA replication and therefore a therapeutic target for cancer. Effective targeting requires knowledge of the mechanism(s) of regulation of this 72 kDa homodimeric enzyme. Here, we investigate the mechanism of binding cooperativity of the nucleotide substrate. We have employed exquisitely sensitive methyl-based CPMG and CEST NMR experiments enabling us to identify residues undergoing bifurcated linear 3-state exchange, including concerted switching between active and inactive conformations in the apo enzyme. The inactive state is populated to only ~1.3%, indicating that conformational selection contributes negligibly to the cooperativity. Instead, methyl rotation axis order parameters, determined by 2H transverse relaxation rates, suggest that rigidification of the enzyme upon substrate binding is responsible for the entropically-driven cooperativity. Lack of the rigidification in product binding and substrate binding to an N-terminally truncated enzyme, both non-cooperative, support this idea. In addition, the lack of this rigidification in the N-terminal truncation indicates that interactions between the flexible N-terminus and the rest of the protein, which are perturbed by substrate binding, play a significant role in the cooperativity—a novel mechanism of dynamic allostery. Together, these findings yield a rare depth of insight into the substrate binding cooperativity of an essential enzyme.
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Affiliation(s)
- Jeffrey P Bonin
- Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina
| | - Paul J Sapienza
- Division of Chemical Biology and Medicinal Chemistry, Eshelman School of Pharmacy, University of North Carolina
| | - Andrew L Lee
- Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina
- Division of Chemical Biology and Medicinal Chemistry, Eshelman School of Pharmacy, University of North Carolina
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Abstract
PULCON (Pulse Length Based Concentration Determination) is a powerful, versatile, non-invasive, and accurate technique for measuring solution concentrations during routine NMR spectroscopy. As solutes are quantified directly by their unique resonances, this technique avoids weight-based errors caused by contaminants (e.g. moisture), allows NMR samples to be directly employed in biological assays, and is particularly useful for quantifying small molecules, peptides, unstable molecules, and other materials that are difficult to weigh or handle. This article provides an introductory guide for biological and medicinal chemists, and highlights the diversity of applications.
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Affiliation(s)
- Jeffrey Y W Mak
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, 4072, Australia
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Sapienza PJ, Popov KI, Mowrey DD, Falk BT, Dokholyan NV, Lee AL. Inter-Active Site Communication Mediated by the Dimer Interface β-Sheet in the Half-the-Sites Enzyme, Thymidylate Synthase. Biochemistry 2019; 58:3302-3313. [PMID: 31283187 DOI: 10.1021/acs.biochem.9b00486] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Thymidylate synthase (TS) is a dimeric enzyme conserved in all life forms that exhibits the allosteric feature of half-the-sites activity. Neither the reason for nor the mechanism of this phenomenon is understood. We used a combined nuclear magnetic resonance (NMR) and molecular dynamics approach to study a stable intermediate preceding hydride transfer, which is the rate-limiting and half-the-sites step. In NMR titrations with ligands leading to this intermediate, we measured chemical shifts of the apoenzyme (lig0), the saturated holoenzyme (lig2), and the typically elusive singly bound (lig1) states. Approximately 40 amides showed quartet patterns providing direct NMR evidence of coupling between the active site and probes >30 Å away in the distal subunit. Quartet peak patterns have symmetrical character, indicating reciprocity in communicating the first and second binding events to the distal protomer. Quartets include key catalytic residues and map to the dimer interface β-sheet, which also represents the shortest path between the two active sites. Simulations corroborate the coupling observed in solution in that there is excellent overlap between quartet residues and main-chain atoms having intersubunit cross-correlated motions. Simulations identify five hot spot residues, three of which lie at the kink in the unique β-bulge abutting the active sites on either end of the sheet. Interstrand cross-correlated motions become more organized and pronounced as the enzyme progresses from lig0 to lig1 and ultimately lig2. Coupling in the apparently symmetrical complex has implications for half-the-sites reactivity and potentially resolves the paradox of inequivalent TS active sites despite the vast majority of X-ray structures appearing to be symmetrical.
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Affiliation(s)
- Paul J Sapienza
- Division of Chemical Biology and Medicinal Chemistry, Eshelman School of Pharmacy , The University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-7355 , United States
| | - Konstantin I Popov
- Department of Biochemistry and Biophysics, School of Medicine , The University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599 , United States
| | - David D Mowrey
- Department of Biochemistry and Biophysics, School of Medicine , The University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599 , United States
| | - Bradley T Falk
- Department of Biochemistry and Biophysics, School of Medicine , The University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599 , United States
| | - Nikolay V Dokholyan
- Department of Pharmacology and Department of Biochemistry and Molecular Biology , Penn State College of Medicine , Hershey , Pennsylvania 17033 , United States.,Department of Chemistry and Department of Biomedical Engineering , The Pennsylvania State University , University Park , Pennsylvania 16801 , United States
| | - Andrew L Lee
- Division of Chemical Biology and Medicinal Chemistry, Eshelman School of Pharmacy , The University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-7355 , United States.,Department of Biochemistry and Biophysics, School of Medicine , The University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599 , United States
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Pozzi C, Lopresti L, Tassone G, Mangani S. Targeting Methyltransferases in Human Pathogenic Bacteria: Insights into Thymidylate Synthase (TS) and Flavin-Dependent TS (FDTS). Molecules 2019; 24:molecules24081638. [PMID: 31027295 PMCID: PMC6514825 DOI: 10.3390/molecules24081638] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2019] [Revised: 04/18/2019] [Accepted: 04/25/2019] [Indexed: 01/10/2023] Open
Abstract
In cells, thymidylate synthases provide the only de novo source of 2′-deoxythymidine-5′-monophosphate (dTMP), required for DNA synthesis. The activity of these enzymes is pivotal for cell survival and proliferation. Two main families of thymidylate synthases have been identified in bacteria, folate-dependent thymidylate synthase (TS) and flavin-dependent TS (FDTS). TS and FDTS are highly divergent enzymes, characterized by exclusive catalytic mechanisms, involving different sets of cofactors. TS and FDTS mechanisms of action have been recently revised, providing new perspectives for the development of antibacterial drugs targeting these enzymes. Nonetheless, some catalytic details still remain elusive. For bacterial TSs, half-site reactivity is still an open debate and the recent evidences are somehow controversial. Furthermore, different behaviors have been identified among bacterial TSs, compromising the definition of common mechanisms. Moreover, the redox reaction responsible for the regeneration of reduced flavin in FDTSs is not completely clarified. This review describes the recent advances in the structural and functional characterization of bacterial TSs and FDTSs and the current understanding of their mechanisms of action. Furthermore, the recent progresses in the development of inhibitors targeting TS and FDTS in human pathogenic bacteria are summarized.
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Affiliation(s)
- Cecilia Pozzi
- Department of Biotechnology, Chemistry and Pharmacy⁻Department of Excellence 2018-2020, University of Siena, via Aldo Moro 2, 53100 Siena, Italy.
| | - Ludovica Lopresti
- Department of Biotechnology, Chemistry and Pharmacy⁻Department of Excellence 2018-2020, University of Siena, via Aldo Moro 2, 53100 Siena, Italy.
| | - Giusy Tassone
- Department of Biotechnology, Chemistry and Pharmacy⁻Department of Excellence 2018-2020, University of Siena, via Aldo Moro 2, 53100 Siena, Italy.
| | - Stefano Mangani
- Department of Biotechnology, Chemistry and Pharmacy⁻Department of Excellence 2018-2020, University of Siena, via Aldo Moro 2, 53100 Siena, Italy.
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Lee AL, Sapienza PJ. Thermodynamic and NMR Assessment of Ligand Cooperativity and Intersubunit Communication in Symmetric Dimers: Application to Thymidylate Synthase. Front Mol Biosci 2018; 5:47. [PMID: 29888227 PMCID: PMC5981203 DOI: 10.3389/fmolb.2018.00047] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Accepted: 04/23/2018] [Indexed: 01/17/2023] Open
Abstract
Thymidylate synthase (TS) is a homodimeric enzyme with evidence for negative regulation of one protomer while the other protomer acts on substrate, so called half-the-sites reactivity. The mechanisms by which multisubunit allosteric proteins communicate between protomers is not well understood, and the simplicity of dimeric systems has advantages for observing conformational and dynamic processes that functionally connect distance-separated active sites. This review considers progress in overcoming the inherent challenges of accurate thermodynamic and atomic-resolution characterization of interprotomer communication mechanisms in symmetric protein dimers, with TS used as an example. Isothermal titration calorimetry (ITC) is used to measure ligand binding cooperativity, even in cases where the two binding enthalpies are similar, and NMR spectroscopy is used to detect site-specific changes occurring in the two protomers. The NMR approach makes use of mixed-labeled dimers, enabling protomer-specific detection of signals in the singly ligated state. The rich informational content of the NMR signals from the singly ligated state, relative to the apo and saturated states, requires new considerations that do not arise in simple cases of 1:1 protein-ligand interactions.
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Affiliation(s)
- Andrew L Lee
- Division of Chemical Biology and Medicinal Chemistry, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
| | - Paul J Sapienza
- Division of Chemical Biology and Medicinal Chemistry, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
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Finer-Moore JS, Lee TT, Stroud RM. A Single Mutation Traps a Half-Sites Reactive Enzyme in Midstream, Explaining Asymmetry in Hydride Transfer. Biochemistry 2018; 57:2786-2795. [PMID: 29717875 DOI: 10.1021/acs.biochem.8b00176] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In Escherichia coli thymidylate synthase (EcTS), rate-determining hydride transfer from the cofactor 5,10-methylene-5,6,7,8-tetrahydrofolate to the intermediate 5-methylene-2'-deoxyuridine 5'-monophosphate occurs by hydrogen tunneling, requiring precise alignment of reactants and a closed binding cavity, sealed by the C-terminal carboxyl group. Mutations that destabilize the closed conformation of the binding cavity allow small molecules such as β-mercaptoethanol (β-ME) to enter the active site and compete with hydride for addition to the 5-methylene group of the intermediate. The C-terminal deletion mutant of EcTS produced the β-ME adduct in proportions that varied dramatically with cofactor concentration, from 50% at low cofactor concentrations to 0% at saturating cofactor conditions, suggesting communication between active sites. We report the 2.4 Å X-ray structure of the C-terminal deletion mutant of E. coli TS in complex with a substrate and a cofactor analogue, CB3717. The structure is asymmetric, with reactants aligned in a manner consistent with hydride transfer in only one active site. In the second site, CB3717 has shifted to a site where the normal cofactor would be unlikely to form 5-methylene-2'-deoxyuridine 5'-monophosphate, consistent with no formation of the β-ME adduct. The structure shows how the binding of the cofactor at one site triggers hydride transfer and borrows needed stabilization from substrate binding at the second site. It indicates pathways through the dimer interface that contribute to allostery relevant to half-sites reactivity.
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Affiliation(s)
- Janet S Finer-Moore
- Department of Biochemistry and Biophysics , University of California , San Francisco , California 94143-2240 , United States
| | - Tom T Lee
- Department of Biochemistry and Biophysics , University of California , San Francisco , California 94143-2240 , United States
| | - Robert M Stroud
- Department of Biochemistry and Biophysics , University of California , San Francisco , California 94143-2240 , United States
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Lisi GP, Loria JP. Allostery in enzyme catalysis. Curr Opin Struct Biol 2017; 47:123-130. [DOI: 10.1016/j.sbi.2017.08.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Revised: 06/27/2017] [Accepted: 08/08/2017] [Indexed: 01/29/2023]
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Altering the allosteric pathway in IGPS suppresses millisecond motions and catalytic activity. Proc Natl Acad Sci U S A 2017; 114:E3414-E3423. [PMID: 28396388 DOI: 10.1073/pnas.1700448114] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Imidazole glycerol phosphate synthase (IGPS) is a V-type allosteric enzyme, meaning that its catalytic rate is critically dependent on activation by its allosteric ligand, N'-[(5'-phosphoribulosyl)formimino]-5-aminoimidazole-4-carboxamide ribonucleotide (PRFAR). The allosteric mechanism of IGPS is reliant on millisecond conformational motions for efficient catalysis. We engineered four mutants of IGPS designed to disrupt millisecond motions and allosteric coupling to identify regions that are critical to IGPS function. Multiple-quantum Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion experiments and NMR chemical shift titrations reveal diminished enzyme flexibility and a reshaping of the allosteric connectivity in each mutant construct, respectively. The functional relevance of the observed motional quenching is confirmed by significant reductions in glutaminase kinetic activity and allosteric ligand binding affinity. This work presents relevant conclusions toward the control of protein allostery and design of unique allosteric sites for potential enzyme inhibitors with regulatory or therapeutic benefit.
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