1
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Galenkamp NS, Maglia G. Single-Molecule Sampling of Dihydrofolate Reductase Shows Kinetic Pauses and an Endosteric Effect Linked to Catalysis. ACS Catal 2022; 12:1228-1236. [PMID: 35096468 PMCID: PMC8787752 DOI: 10.1021/acscatal.1c04388] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Revised: 12/13/2021] [Indexed: 12/21/2022]
Abstract
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The ability to sample multiple reactions
on the same single enzyme
is important to link rare intermediates with catalysis and to unravel
the role of conformational changes. Despite decades of efforts, however,
the single-molecule characterization of nonfluorogenic enzymes during
multiple catalytic turnovers has been elusive. Here, we show that
nanopore currents allow sampling the dynamic exchange between five
structural intermediates during E. coli dihydrofolate reductase (DHFR) catalysis. We found that an endosteric
effect promotes the binding of the substrate to the enzyme with a
specific hierarchy. The chemical step then switched the enzyme from
the closed to the occluded conformation, which in turn promotes the
release of the reduced cofactor NADP+. Unexpectedly, only
a few reactive complexes lead to catalysis. Furthermore, second-long
catalytic pauses were observed, possibly reflecting an off-path conformation
generated during the reaction. Finally, the free energy from multiple
cofactor binding events were required to release the product and switch
DHFR back to the reactive conformer. This catalytic fueled concerted
mechanism is likely to have evolved to improve the catalytic efficiency
of DHFR under the high concentrations of NADP+ in E. coli and might be a general feature for complex
enzymatic reactions where the binding and release of the products
must be tightly controlled.
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Affiliation(s)
- Nicole Stéphanie Galenkamp
- Groningen Biomolecular Sciences and Biotechnology (GBB) Institute, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
| | - Giovanni Maglia
- Groningen Biomolecular Sciences and Biotechnology (GBB) Institute, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
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2
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Directional conformer exchange in dihydrofolate reductase revealed by single-molecule nanopore recordings. Nat Chem 2020; 12:481-488. [DOI: 10.1038/s41557-020-0437-0] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Accepted: 02/10/2020] [Indexed: 12/18/2022]
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3
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A novel method to determine antibiotic sensitivity in Bdellovibrio bacteriovorus reveals a DHFR-dependent natural trimethoprim resistance. Sci Rep 2020; 10:5315. [PMID: 32210253 PMCID: PMC7093396 DOI: 10.1038/s41598-020-62014-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Accepted: 03/04/2020] [Indexed: 11/13/2022] Open
Abstract
Bdellovibrio bacteriovorus is a small Gram-negative bacterium and an obligate predator of other Gram-negative bacteria. Prey resistance to B. bacteriovorus attack is rare and transient. This consideration together with its safety and low immunogenicity makes B. bacteriovorus a valid alternative to antibiotics, especially in the treatment of multidrug resistant pathogens. In this study we developed a novel technique to estimate B. bacteriovorus sensitivity against antibiotics in order to make feasible the development and testing of co-therapies with antibiotics that would increase its antimicrobial efficacy and at the same time reduce the development of drug resistance. Results from tests performed with this technique show that among all tested antibiotics, trimethoprim has the lowest antimicrobial effect on B. bacteriovorus. Additional experiments revealed that the mechanism of trimethoprim resistance in B. bacteriovorus depends on the low affinity of this compound for the B. bacteriovorus dihydrofolate reductase (Bd DHFR).
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4
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Acosta LC, Perez Goncalves GM, Pielak GJ, Gorensek-Benitez AH. Large cosolutes, small cosolutes, and dihydrofolate reductase activity. Protein Sci 2017; 26:2417-2425. [PMID: 28971539 DOI: 10.1002/pro.3316] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Revised: 09/27/2017] [Accepted: 09/27/2017] [Indexed: 11/06/2022]
Abstract
Protein enzymes are the main catalysts in the crowded and complex cellular interior, but their activity is almost always studied in dilute buffered solutions. Studies that attempt to recreate the cellular interior in vitro often utilize synthetic polymers as crowding agents. Here, we report the effects of the synthetic polymer cosolutes Ficoll, dextran, and polyvinylpyrrolidone, and their respective monomers, sucrose, glucose, and 1-ethyl-2-pyrrolidone, on the activity of the 18-kDa monomeric enzyme, Escherichia coli dihydrofolate reductase. At low concentrations, reductase activity increases relative to buffer and monomers, suggesting a macromolecular effect. However, the effect decreases at higher concentrations, approaching, and, in some cases, falling below buffer values. We also assessed activity in terms of volume occupancy, viscosity, and the overlap concentration (where polymers form an interwoven mesh). The trends vary with polymer family, but changes in activity are within threefold of buffer values. We also compiled and analyzed results from previous studies and conclude that alterations of steady-state enzyme kinetics in solutions crowded with synthetic polymers are idiosyncratic with respect to the crowding agent and enzyme.
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Affiliation(s)
| | | | - Gary J Pielak
- Department of Chemistry.,Department of Biochemistry and Biophysics.,Lineberger Comprehensive Cancer Center.,Integrative Program for Biological and Genome Sciences University of North Carolina, Chapel Hill, NC, 27599, USA
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5
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Kwon YJ, Sohn MJ, Kim HJ, Kim WG. The Lactone Form of Stachybotrydial: A New Inhibitor of Dihydrofolate Reductase from Stachybotrys sp. FN298. Biol Pharm Bull 2014; 37:1406-10. [DOI: 10.1248/bpb.b14-00108] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Yun-Ju Kwon
- Superbacteria Research Center, Korea Research Institute of Bioscience and Biotechnology
| | - Mi-Jin Sohn
- Superbacteria Research Center, Korea Research Institute of Bioscience and Biotechnology
| | - Hyun-Ju Kim
- Superbacteria Research Center, Korea Research Institute of Bioscience and Biotechnology
| | - Won-Gon Kim
- Superbacteria Research Center, Korea Research Institute of Bioscience and Biotechnology
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6
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Carroll MJ, Mauldin RV, Gromova AV, Singleton SF, Collins EJ, Lee AL. Evidence for dynamics in proteins as a mechanism for ligand dissociation. Nat Chem Biol 2012; 8:246-52. [PMID: 22246400 PMCID: PMC3288659 DOI: 10.1038/nchembio.769] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2011] [Accepted: 11/23/2011] [Indexed: 01/16/2023]
Abstract
Signal transduction, regulatory processes, and pharmaceutical responses are highly dependent upon ligand residence times. Gaining insight into how physical factors influence residence times, or koff, should enhance our ability to manipulate biological interactions. We report experiments that yield structural insight into koff for a series of eight 2,4-diaminopyrimidine inhibitors of dihydrofolate reductase that vary by six orders of magnitude in binding affinity. NMR relaxation dispersion experiments revealed a common set of residues near the binding site that undergo a concerted, millisecond-timescale switching event to a previously unidentified conformation. The rate of switching from ground to excited conformations correlates exponentially with Ki and koff, suggesting that protein dynamics serves as a mechanical initiator of ligand dissociation within this series and potentially for other macromolecule-ligand systems. Although kconf,forward is faster than koff, use of the ligand series allowed for connections to be drawn between kinetic events on different timescales.
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Affiliation(s)
- Mary J Carroll
- Division of Chemical Biology and Medicinal Chemistry, Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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7
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Torres-Cortés G, Millán V, Ramírez-Saad HC, Nisa-Martínez R, Toro N, Martínez-Abarca F. Characterization of novel antibiotic resistance genes identified by functional metagenomics on soil samples. Environ Microbiol 2011; 13:1101-14. [PMID: 21281423 DOI: 10.1111/j.1462-2920.2010.02422.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The soil microbial community is highly complex and contains a high density of antibiotic-producing bacteria, making it a likely source of diverse antibiotic resistance determinants. We used functional metagenomics to search for antibiotic resistance genes in libraries generated from three different soil samples, containing 3.6 Gb of DNA in total. We identified 11 new antibiotic resistance genes: 3 conferring resistance to ampicillin, 2 to gentamicin, 2 to chloramphenicol and 4 to trimethoprim. One of the clones identified was a new trimethoprim resistance gene encoding a 26.8 kDa protein closely resembling unassigned reductases of the dihydrofolate reductase group. This protein, Tm8-3, conferred trimethoprim resistance in Escherichia coli and Sinorhizobium meliloti (γ- and α-proteobacteria respectively). We demonstrated that this gene encoded an enzyme with dihydrofolate reductase activity, with kinetic constants similar to other type I and II dihydrofolate reductases (K(m) of 8.9 µM for NADPH and 3.7 µM for dihydrofolate and IC(50) of 20 µM for trimethoprim). This is the first description of a new type of reductase conferring resistance to trimethoprim. Our results indicate that soil bacteria display a high level of genetic diversity and are a reservoir of antibiotic resistance genes, supporting the use of this approach for the discovery of novel enzymes with unexpected activities unpredictable from their amino acid sequences.
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Affiliation(s)
- Gloria Torres-Cortés
- Genetic Ecology Group, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Calle Profesor Albareda 1, 18008 Granada, Spain
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8
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Redecke L, Brehm MA, Bredehorst R. Cloning and characterization of dihydrofolate reductase from a facultative alkaliphilic and halotolerant bacillus strain. Extremophiles 2006; 11:75-83. [PMID: 17021659 DOI: 10.1007/s00792-006-0013-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2006] [Accepted: 06/30/2006] [Indexed: 10/24/2022]
Abstract
Elucidation of the molecular basis of the stability of enzymes from extremophilic organisms is of fundamental importance for various industrial applications. Due to the wealth of structural data from various species, dihydrofolate reductase (DHFR, EC 1.5.1.3) provides an excellent model for systematic investigations. In this report, DHFR from alkaliphilic Bacillus halodurans C-125 was cloned and expressed in E. coli. Functional analyses revealed that BhDHFR exhibits the most alkali-stable phenotype of DHFRs characterized so far. Optimal enzyme activity was observed in a slightly basic pH region ranging from 7.25 to 8.75. Alkali-stability is associated with a remarkable resistance to elevated temperatures (half-life of 60 min at 52.5 degrees C) and to high concentrations of urea (up to 3 M). Although the secondary structure shows distinct similarities to those of mesophilic DHFR molecules, BhDHFR exhibits molecular features contributing to its alkaliphilic properties. Interestingly, the unique phenotype is diminished by C-terminal addition of a His-tag sequence. Therefore, His-tag-derivatized BhDHFR offers the opportunity to obtain deeper insights into the specific mechanisms of alkaliphilic adaption by comparison of the three dimensional structure of both BhDHFR molecules.
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Affiliation(s)
- Lars Redecke
- Institute of Biochemistry and Food Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, 20146, Hamburg, Germany.
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9
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Kley N. Chemical dimerizers and three-hybrid systems: scanning the proteome for targets of organic small molecules. ACTA ACUST UNITED AC 2005; 11:599-608. [PMID: 15157871 DOI: 10.1016/j.chembiol.2003.09.017] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The integration of technological advances in areas as diverse as chemical biology, proteomics, genomics, automation, and bioinformatics has led to the emergence of novel screening paradigms for analyzing the molecular basis of drug action. This review summarizes recent advances in three-hybrid technologies and their application to the characterization of small molecule-protein interactions and proteome-wide identification of drug receptors.
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Affiliation(s)
- Nikolai Kley
- GPC Biotech Inc., 610 Lincoln Street, Waltham, MA 02451 USA.
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10
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Maskell JP, Sefton AM, Hall LM. Multiple mutations modulate the function of dihydrofolate reductase in trimethoprim-resistant Streptococcus pneumoniae. Antimicrob Agents Chemother 2001; 45:1104-8. [PMID: 11257022 PMCID: PMC90431 DOI: 10.1128/aac.45.4.1104-1108.2001] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2000] [Accepted: 01/12/2001] [Indexed: 11/20/2022] Open
Abstract
Trimethoprim resistance in Streptococcus pneumoniae can be conferred by a single amino acid substitution (I100-L) in dihydrofolate reductase (DHFR), but resistant clinical isolates usually carry multiple DHFR mutations. DHFR genes from five trimethoprim-resistant isolates from the United Kingdom were compared to susceptible isolates and used to transform a susceptible control strain (CP1015). All trimethoprim-resistant isolates and transformants contained the I100-L mutation. The properties of DHFRs from transformants with different combinations of mutations were compared. In a transformant with only the I100-L mutation (R12/T2) and a D92-A mutation also found in the DHFRs of susceptible isolates, the enzyme was much more resistant to trimethoprim inhibition (50% inhibitory concentration [IC50], 4.2 microM) than was the DHFR from strain CP1015 (IC50, 0.09 microM). However, Km values indicated a lower affinity for the enzyme's natural substrates (Km for dihydrofolate [DHF], 3.1 microM for CP1015 and 27.5 microM for R12/T2) and a twofold decrease in the specificity constant. In transformants with additional mutations in the C-terminal portion of the enzyme, Km values for DHF were reduced (9.2 to 15.2 microM), indicating compensation for the lower affinity generated by I100-L. Additional mutations in the N-terminal portion of the enzyme were associated with up to threefold-increased resistance to trimethoprim (IC50 of up to 13.7 microM). It is postulated that carriage of the mutation M53-I-which, like I100-L, corresponds to a trimethoprim binding site in the Escherichia coli DHFR-is responsible for this increase. This study demonstrates that although the I100-L mutation alone may give rise to trimethoprim resistance, additional mutations serve to enhance resistance and modulate the effects of existing mutations on the affinity of DHFR for its natural substrates.
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Affiliation(s)
- J P Maskell
- Department of Medical Microbiology, St. Bartholomew's and the Royal London School of Medicine and Dentistry, London E1 2AD, United Kingdom.
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11
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Ma L, Kovacs JA. Expression and characterization of recombinant human-derived Pneumocystis carinii dihydrofolate reductase. Antimicrob Agents Chemother 2000; 44:3092-6. [PMID: 11036028 PMCID: PMC101608 DOI: 10.1128/aac.44.11.3092-3096.2000] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Dihydrofolate reductase (DHFR) is the target of trimethoprim (TMP), which has been widely used in combination with sulfa drugs for treatment and prophylaxis of Pneumocystis carinii pneumonia. While the rat-derived P. carinii DHFR has been well characterized, kinetic studies of human-derived P. carinii DHFR, which differs from rat-derived P. carinii DHFR by 38% in amino acid sequence, have not been reported to date. Here we report on the expression and kinetic characterization of the recombinant human-derived P. carinii DHFR. The 618-bp coding sequence of the human-derived P. carinii DHFR gene was expressed in Escherichia coli. As determined by sodium dodecyl sulfate-polyacrylamide gel eletrophoresis, the purified enzyme had a molecular mass of 25 kDa, consistent with that predicted from the DNA sequence. Kinetic analysis showed that the K(m) values for dihydrofolate and NADPH were 2.7 +/- 0.3 and 14.0 +/- 4.3 microM, respectively, which are similar to those reported for rat-derived P. carinii DHFR. Inhibition studies revealed that both TMP and pyrimethamine were poor inhibitors of human-derived P. carinii DHFR, with K(i) values of 0.28 +/- 0.08 and 0.065 +/- 0.005 microM, respectively, while trimetrexate and methotrexate were potent inhibitors, with K(i) values of 0.23 +/- 0.03 and 0.016 +/- 0.004 nM, respectively. The availability of purified recombinant enzyme in large quantities should facilitate the identification of antifolate inhibitors with greater potency and higher selectivity for human-derived P. carinii DHFR.
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Affiliation(s)
- L Ma
- Critical Care Medicine Department, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, Maryland, USA
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12
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Walker VK, Tyshenko MG, Kuiper MJ, Dargar RV, Yuhas DA, Cruickshank PA, Chaguturu R. Tobacco budworm dihydrofolate reductase is a promising target for insecticide discovery. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:394-403. [PMID: 10632709 DOI: 10.1046/j.1432-1327.2000.01009.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Structural differences in dihydrofolate reductases from different species have been exploited to develop specific inhibitory molecules, such as chemotherapeutic agents, antibiotics or antihelminthics, that show species specificity or selectivity. As dihydrofolate reductase (DHFR) is a crucial enzyme for the synthesis of purines, pyrimidines and some amino acids, and also because developing insects show a remarkably rapid rate of cell division, DHFR is a potentially promising target for the discovery of novel insecticides. We have thus isolated and characterized the enzyme from a serious agricultural pest, Heliothis (Helicoverpa) virescens, the tobacco budworm. Sequencing tryptic peptides of the 35 000-fold purified DHFR allowed the subsequent isolation of a partial cDNA, with the full Dhfr gene sequence obtained from a genomic library. The H. virescens Dhfr spans 4 kb, with three introns, and encodes 185 amino acids. The enzyme shows an overall similarity of approximately 68% with DHFR from other metazoans, which has facilitated the molecular modeling of the protein. DHFRs from insects appear to have strikingly reduced sensitivity to inhibition by methotrexate, compared with the vertebrate enzymes, and this reduction was also reflected in the total binding energy seen after modeling experiments. Four residues that may be characteristic of insect DHFR, as well as a unique cysteine in the H. virescens DHFR active site, offer insight into the nature of inhibitor selectivity and provide suitable target sites for insecticide discovery.
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Affiliation(s)
- V K Walker
- Department of Biology, Queen's University, Kingston, Ontario, Canada.
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13
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Reynolds MG, Roos DS. A biochemical and genetic model for parasite resistance to antifolates. Toxoplasma gondii provides insights into pyrimethamine and cycloguanil resistance in Plasmodium falciparum. J Biol Chem 1998; 273:3461-9. [PMID: 9452469 DOI: 10.1074/jbc.273.6.3461] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We have exploited the experimental accessibility of the protozoan parasite Toxoplasma gondii and its similarity to Plasmodium falciparum to investigate the influence of specific dihydrofolate reductase polymorphisms known from field isolates of drug-resistant malaria. By engineering appropriate recombinant shuttle vectors, it is feasible to examine mutations by transient or stable transformation of T. gondii parasites, in bacterial and yeast complementation assays, and through biochemical analysis of purified enzyme. A series of mutant alleles that mirror P. falciparum variants reveals that the key mutation Asn-108 (Asn-83 in T. gondii) probably confers resistance to pyrimethamine by affecting critical interactions in the ternary complex. Mutations such as Arg-59 (T. gondii 36) have limited effect in isolation, but in combination with other mutations they enhance the competitive ability of folate by increasing the speed of product turnover. Val-16 (T. gondii 10) confers low level resistance to cycloguanil but hypersensitivity to pyrimethamine. This mutation precludes Asn-108, probably because compression of the folate binding pocket introduced by this combination is incompatible with enzyme function. These studies permit detailed biochemical, kinetic, and structural analysis of drug resistance mutations and reconstruction of the probable phylogeny of antifolate resistance in malaria.
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Affiliation(s)
- M G Reynolds
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6018, USA
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14
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Hsu MC, Ho Y, Huang FY. Dihydrofolate Reductase from E. coliCatalyzes the Oxygen-Dependent Oxidation of NADPH in the Absense of Folates. J CHIN CHEM SOC-TAIP 1998. [DOI: 10.1002/jccs.199800020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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15
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Köhler T, Kok M, Michea-Hamzehpour M, Plesiat P, Gotoh N, Nishino T, Curty LK, Pechere JC. Multidrug efflux in intrinsic resistance to trimethoprim and sulfamethoxazole in Pseudomonas aeruginosa. Antimicrob Agents Chemother 1996; 40:2288-90. [PMID: 9036831 PMCID: PMC163521 DOI: 10.1128/aac.40.10.2288] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Pseudomonas aeruginosa possesses at least two multiple drug efflux systems which are defined by the outer membrane proteins OprM and OprJ. We have found that mutants overexpressing OprM were two- and eightfold more resistant than their wild-type parent to sulfamethoxazole (SMX) and trimethoprim (TMP), respectively. For OprJ-overproducing strains, MICs of TMP increased fourfold but those of SMX were unchanged. Strains overexpressing OprM, but not those overexpressing OprJ, became hypersusceptible to TMP and SMX when oprM was inactivated. The wild-type antibiotic profile could be restored in an oprM mutant by transcomplementation with the cloned oprM gene. These results demonstrate that the mexABoprM multidrug efflux system is mainly responsible for the intrinsic resistance of P. aeruginosa to TMP and SMX.
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Affiliation(s)
- T Köhler
- Department of Genetics and Microbiology, Centre Médical Universitaire, Geneva, Switzerland.
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16
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Marszal E, Scouten WH. Dihydrofolate reductase synthesis in the presence of immobilized methotrexate. An approach to a continuous cell-free protein synthesis system. J Mol Recognit 1996; 9:543-8. [PMID: 9174938 DOI: 10.1002/(sici)1099-1352(199634/12)9:5/6<543::aid-jmr298>3.0.co;2-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Dihydrofolate reductase was synthesized in a batch system in the presence of the affinity ligand methotrexate, bound to various matrices. Two types of gel were used: commercial methotrexate-agarose with pores inaccessible for translation machinery and methotrexate-POROS with pores easily accessible for translation reaction mixture components. The transcription/translation reaction was not inhibited by either the immobilized methotrexate or the matrix. The enzyme was synthesized with a high yield and could simultaneously be removed from the reaction mixture by the affinity matrix during the synthesis. With methotrexate-POROS present the reaction probably proceeded mainly in the pores of the gel. Kinetic limitations to the reaction in the presence of the gel were not observed. Active dihydrofolate reductase was eluted from methotrexate-POROS. The activity recovered was higher than dihydrofolate reductase activity synthesized in free solution system. The influence of the presence of immobilized methotrexate on dihydrofolate reductase synthesis will be further studied in a novel type of a continuous protein synthesis system.
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Affiliation(s)
- E Marszal
- Biotechnology Center, Utah State University, Logan 84322-4700, USA
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17
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Kuyper LF, Baccanari DP, Jones ML, Hunter RN, Tansik RL, Joyner SS, Boytos CM, Rudolph SK, Knick V, Wilson HR, Caddell JM, Friedman HS, Comley JC, Stables JN. High-affinity inhibitors of dihydrofolate reductase: antimicrobial and anticancer activities of 7,8-dialkyl-1,3-diaminopyrrolo[3,2-f]quinazolines with small molecular size. J Med Chem 1996; 39:892-903. [PMID: 8632413 DOI: 10.1021/jm9505122] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
A series of 7,8-dialkylpyrrolo[3,2-f]quinazolines were prepared as inhibitors of dihydrofolate reductase (DHFR). On the basis of an apparent inverse relationship between compound size and antifungal activity, the compounds were designed to be relatively small and compact. Inhibitor design was aided by GRID analysis of the three-dimensional structure of Candida albicans DHFR, which suggested that relatively small, branched alkyl groups at the 7- and 8-positions of the pyrroloquinazoline ring system would provide optimal interactions with a hydrophobic region of the protein. The compounds were potent inhibitors of fungal and human DHFR, with K(i) values as low as 7.1 and 0.1 pM, respectively, and were highly active against C. albicans and an array of tumor cell lines. In contrast to known lipophilic inhibitors of DHFR such as trimetrexate and piritrexim, members of this series of pyrroloquinazolines were not susceptible to P-glycoprotein-mediated multidrug resistance and also showed significant distribution into lung and brain tissue. The compounds were active in lung and brain tumor models and displayed in vivo activity against Pneumocystis carinii and C. albicans.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily B, Member 1/drug effects
- Animals
- Anti-Infective Agents/chemical synthesis
- Anti-Infective Agents/pharmacology
- Anti-Infective Agents/toxicity
- Antineoplastic Agents/chemical synthesis
- Antineoplastic Agents/pharmacology
- Antineoplastic Agents/toxicity
- Brain Neoplasms/drug therapy
- Candidiasis/drug therapy
- Cell Division/drug effects
- Cell Line
- Crystallography, X-Ray
- Drug Design
- Drug Resistance, Multiple
- Enzyme Inhibitors/chemical synthesis
- Enzyme Inhibitors/pharmacology
- Folic Acid Antagonists/chemistry
- Humans
- Lung Neoplasms/drug therapy
- Magnetic Resonance Spectroscopy
- Mass Spectrometry
- Mice
- Mice, Nude
- Mice, SCID
- Models, Molecular
- Molecular Conformation
- Molecular Structure
- Molecular Weight
- Pneumonia, Pneumocystis/drug therapy
- Protein Structure, Secondary
- Quinazolines/chemical synthesis
- Quinazolines/pharmacology
- Quinazolines/toxicity
- Structure-Activity Relationship
- Toxoplasma/drug effects
- Tumor Cells, Cultured
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Affiliation(s)
- L F Kuyper
- Wellcome Research Laboratories, Research Triangle Park, North Carolina 27709, USA
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18
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Dale GE, Langen H, Page MG, Then RL, Stüber D. Cloning and characterization of a novel, plasmid-encoded trimethoprim-resistant dihydrofolate reductase from Staphylococcus haemolyticus MUR313. Antimicrob Agents Chemother 1995; 39:1920-4. [PMID: 8540692 PMCID: PMC162857 DOI: 10.1128/aac.39.9.1920] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
In recent years resistance to the antibacterial agent trimethoprim (Tmp) has become more widespread, and several trimethoprim-resistant (Tmpr) dihydrofolate reductases (DHFRs) have been described from gram-negative bacteria. In staphylococci, only one Tmpr DHFR has been described, the type S1 DHFR, which is encoded by the dfrA gene found on transposon Tn4003. In order to investigate the coincidence of high-level Tmp resistance and the presence of dfrA, we analyzed the DNAs from various Tmpr staphylococci for the presence of dfrA sequences by PCR with primers specific for the thyE-dfrA genes from Tn4003. We found that 30 or 33 isolates highly resistant to Tmp (MICs, > or = 512 micrograms/ml) contained dfrA sequences, whereas among the Tmpr (MICs, < or = 256 micrograms/ml) and Tmps isolates only the Staphylococcus epidermidis isolates (both Tmpr and Tmps) seemed to contain the dfrA gene. Furthermore, we have cloned and characterized a novel, plasmid-encoded Tmpr DHFR from Staphylococcus haemolyticus MUR313. The dfrD gene of plasmid pABU17 is preceded by two putative Shine-Dalgarno sequences potentially allowing for the start of translation at two triplets separated by nine nucleotides. The predicted protein of 166 amino acids, designated S2DHFR, encoded by the longer open reading frame was overproduced in Escherichia coli, purified, and characterized. The molecular size of the recombinant S2DHFR was determined by ion spray mass spectrometry to be 19,821.2 +/- 2 Da, which is in agreement with the theoretical value of 19,822 Da. In addition, the recombinant S2DHFR was shown to exhibit DHFR activity and to be highly resistant to Tmp.
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Affiliation(s)
- G E Dale
- Department of Gene Technologies, F. Hoffmann-La Roche Ltd., Basel, Switzerland
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19
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Dale GE, Broger C, Hartman PG, Langen H, Page MG, Then RL, Stüber D. Characterization of the gene for the chromosomal dihydrofolate reductase (DHFR) of Staphylococcus epidermidis ATCC 14990: the origin of the trimethoprim-resistant S1 DHFR from Staphylococcus aureus? J Bacteriol 1995; 177:2965-70. [PMID: 7768789 PMCID: PMC176980 DOI: 10.1128/jb.177.11.2965-2970.1995] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The gene for the chromosomally encoded dihydrofolate reductase (DHFR) of Staphylococcus epidermidis ATCC 14990 has been cloned and characterized. The structural gene encodes a polypeptide of 161 amino acid residues with a calculated molecular weight of 18,417. This trimethoprim-sensitive (Tmps) DHFR, SeDHFR, differs in only three amino acids (Val-31-->Ile, Gly-43-->Ala, and Phe-98-->Tyr) from the trimethoprim-resistant (Tmpr) S1 DHFR encoded by transposon Tn4003. Since in addition the S. epidermidis gene also forms part of an operon with thyE and open reading frame 140 as in Tn4003, the chromosomally located gene encoding the Tmps SeDHFR is likely to be the molecular origin of the plasmid-located gene encoding the Tmpr S1 DHFR. Site-directed mutagenesis and kinetic analysis of the purified enzymes suggest that a single Phe-->Tyr change at position 98 is the major determinant of trimethoprim resistance.
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Affiliation(s)
- G E Dale
- Department of Gene Technologies, F. Hoffmann-La Roche Ltd., Basel, Switzerland
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20
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Sasso SP, Gilli RM, Sari JC, Rimet OS, Briand CM. Thermodynamic study of dihydrofolate reductase inhibitor selectivity. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1207:74-9. [PMID: 8043612 DOI: 10.1016/0167-4838(94)90053-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The thermodynamic parameters of the binding of some folate analogues (methotrexate, trimetrexate and trimethoprim) to dihydrofolate reductases from different species have been measured with a flow microcalorimetric method at 37 degrees C. In the absence of NADPH, the three inhibitors exhibited a higher affinity for E. coli DHFR than for vertebrate DHFRs. This selectivity in favor of bacterial DHFR is entropy driven and is correlated with a weaker conformational change for bacterial DHFR than for vertebrate DHFRs, and with additional hydrophobic contacts, provided by this enzyme to the ligands. In presence of NADPH, as reported in the literature, trimetoprim shows a high selectivity in favor of bacterial DHFR, contrarily to methotrexate and trimetrexate, whose affinities are elevated and highly similar for mammalian and bacterial enzymes. The positive cooperative effect of NADPH, which has an enthalpic origin, fluctuates widely with inhibitor structure and with enzyme species. For trimethoprim, the cooperative effect is much more pronounced for bacterial DHFR than for vertebrate DHFRs. But the role of NADPH is not to induce a selectivity: it only increases the selectivity that trimethoprim already presented in absence of NADPH. Inversely, for methotrexate and trimetrexate, the cooperative effect is stronger for vertebrate enzymes than for the bacterial enzyme, and thus, NADPH cancels the selectivity the two antifolic compounds had, in the absence of NADPH, for the bacterial enzyme.
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Affiliation(s)
- S P Sasso
- Groupe de Recherche sur les Interactions des Protéines en Pharmacologie (G.R.I.P.P.), Laboratoire de Physique Pharmaceutique, Faculté de Pharmacie, Marseille, France
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21
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Dale GE, Then RL, Stüber D. Characterization of the gene for chromosomal trimethoprim-sensitive dihydrofolate reductase of Staphylococcus aureus ATCC 25923. Antimicrob Agents Chemother 1993; 37:1400-5. [PMID: 8363365 PMCID: PMC187982 DOI: 10.1128/aac.37.7.1400] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The gene for the trimethoprim-sensitive (Tmps) chromosomal dihydrofolate reductase (DHFR) of Staphylococcus aureus ATCC 25923 was cloned and characterized. The structural gene encodes a polypeptide of 159 amino acid residues and has a calculated molecular weight of 18,251. The amino acid sequences of this Tmps DHFR and those of the trimethoprim-resistant type S1 DHFR encoded by transposon Tn4003 are 80% identical. In contrast to the trimethoprim-resistant enzyme, the Tmps DHFR can be highly overexpressed in Escherichia coli, with most of the recombinant protein occurring in a soluble and an active form.
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Affiliation(s)
- G E Dale
- Department of New Technologies, F. Hoffmann-La Roche Ltd., Basel, Switzerland
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22
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23
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Then RL, Hartman PG, Kompis I, Santi D. Selective inhibition of dihydrofolate reductase from problem human pathogens. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1993; 338:533-6. [PMID: 8304174 DOI: 10.1007/978-1-4615-2960-6_108] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- R L Then
- F. Hoffmann-La Roche Ltd, Basel/Switzerland
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24
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Dale GE, Stüber D, Broger C, Langen H. Expression of the trimethoprim resistant dihydrofolate reductase encoded by transposon TN4003 in a soluble form and its subsequent purification to homogeneity. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1993; 338:541-4. [PMID: 8304176 DOI: 10.1007/978-1-4615-2960-6_110] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
A high level expression in E. coli of the Tmpr type S1 DHFR was achieved by: (1) elimination of an internal start of translation within the RNA, and (2) optimization of gene expression by replacing nucleotides at the 5' end of the gene by nucleotides present in the highly expressible gene for SaDHFR. In addition, by replacing amino acids supposed to be on the surface of the protein, the mutein S1 DHFR[N48E,N130D] was constructed, which can be expressed in E. coli to high levels in a soluble and active form. The mutein S1 DHFR[N48E,N130D] was purified nearly to homogeneity. The enzyme is highly active and remains soluble even at a protein concentration of 10 mg/ml.
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Affiliation(s)
- G E Dale
- F. Hoffmann-La Roche Ltd., Pharmaceutical Research-New Technologies, Basel, Switzerland
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25
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Resto E, Iida A, Van Cleve MD, Hecht SM. Amplification of protein expression in a cell free system. Nucleic Acids Res 1992; 20:5979-83. [PMID: 1281316 PMCID: PMC334463 DOI: 10.1093/nar/20.22.5979] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Large quantities of a catalytically active protein have been produced in a cell free system. More than 10(9) copies of protein were produced from each DNA plasmid containing DNAfol, the bacterial gene encoding dihydrofolate reductase (DHFR). The strategy employed, denoted gene amplification with transcription/translation (GATT), involves sequential coupling of (i) DNA amplification by the polymerase chain reaction (PCR) and (ii) in vitro RNA transcription by T7 RNA polymerase, followed by (iii) translation of the run-off transcripts in a rabbit reticulocyte system. The protein product had the expected size (18 kDa) and catalyzed the NADPH-dependent reduction of 7,8-dihydrofolic acid to 5,6,7,8-tetrahydrofolic acid as efficiently as authentic DHFR. Potential applications of the strategy include large scale production of enzymes containing synthetic amino acids and facilitation of the characterization of the function of genes encountered in genomic mapping studies.
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Affiliation(s)
- E Resto
- Department of Chemistry, University of Virginia, Charlottesville 22901
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26
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Kudlicki W, Kramer G, Hardesty B. High efficiency cell-free synthesis of proteins: refinement of the coupled transcription/translation system. Anal Biochem 1992; 206:389-93. [PMID: 1332549 DOI: 10.1016/0003-2697(92)90383-i] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Two modifications are introduced to convert the Escherichia coli cell-free extract ("S30") into a high efficiency system for coupled transcription/translation of exogenously added genes. (a) The ribosome fraction collected from the S30 by ultracentrifugation is used. It contains all the proteins necessary for gene expression but has lost the vast majority of soluble proteins that might interfere with purification and enzymatic activity of product formed. (b) Plasmids containing coding sequences to be expressed are not linearized thus enhancing their stability by avoiding their degradation. These two modifications not only improve protein synthesis in a static system but allow gene expression over 20-40 h in the continuous-flow cell-free system. Both prokaryotic and eukaryotic proteins have been synthesized in this system.
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Affiliation(s)
- W Kudlicki
- Department of Chemistry and Biochemistry, University of Texas, Austin 78712
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27
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Bystroff C, Kraut J. Crystal structure of unliganded Escherichia coli dihydrofolate reductase. Ligand-induced conformational changes and cooperativity in binding. Biochemistry 1991; 30:2227-39. [PMID: 1998681 DOI: 10.1021/bi00222a028] [Citation(s) in RCA: 153] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The crystal structure of unliganded dihydrofolate reductase (DHFR) from Escherichia coli has been solved and refined to an R factor of 19% at 2.3-A resolution in a crystal form that is nonisomorphous with each of the previously reported E. coli DHFR crystal structures [Bolin, J. T., Filman, D. J., Matthews, D. A., Hamlin, B. C., & Kraut, J. (1982) J. Biol. Chem. 257, 13650-13662; Bystroff, C., Oatley, S. J., & Kraut, J. (1990) Biochemistry 29, 3263-3277]. Significant conformational changes occur between the apoenzyme and each of the complexes: the NADP+ holoenzyme, the folate-NADP+ ternary complex, and the methotrexate (MTX) binary complex. The changes are small, with the largest about 3 A and most of them less than 1 A. For simplicity a two-domain description is adopted in which one domain contains the NADP+ 2'-phosphate binding site and the binding sites for the rest of the coenzyme and for the substrate lie between the two domains. Binding of either NADP+ or MTX induces a closing of the PABG-binding cleft and realignment of alpha-helices C and F which bind the pyrophosphate of the coenzyme. Formation of the ternary complex from the holoenzyme does not involve further relative domain shifts but does involve a shift of alpha-helix B and a floppy loop (the Met-20 loop) that precedes alpha B. These observations suggest a mechanism for cooperativity in binding between substrate and coenzyme wherein the greatest degree of cooperativity is expressed in the transition-state complex. We explore the idea that the MTX binary complex in some ways resembles the transition-state complex.
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Affiliation(s)
- C Bystroff
- Department of Chemistry, University of California, San Diego, La Jolla 92093
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28
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Rimet O, Chauvet M, Sarrazin M, Bourdeaux M. Conformational change induced by coenzyme binding to bovine liver dihydrofolate reductase: a spectrofluorimetric study. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1076:435-8. [PMID: 2001392 DOI: 10.1016/0167-4838(91)90488-l] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
When NADPH was added in excess to a bovine liver DHFR solution, a fluorescence peak due to an energy transfer mechanism was apparent at 450 nm. It did not vary over time. The intrinsic fluorescence peak of DHFR at 320 nm was quenched and this phenomenon increased over the time-course after NADPH addition. This result was ascribed to a slow DHFR conformational change induced by NADPH binding, which has never been previously described in such a long time scale (more than 30 min). A kinetic scheme accounting for this mechanism has been proposed. Furthermore, this interconversion between two protein conformers led to an increase in the initial apparent rate of the enzymatic reaction catalyzed by DHFR.
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Affiliation(s)
- O Rimet
- Département de Physique, UFR de Pharmacie, Marseille, France
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29
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Baccanari DP, Tansik RL, Joyner SS, Fling ME, Smith PL, Freisheim JH. Characterization of Candida albicans Dihydrofolate Reductase. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)85059-7] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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30
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Hartman PG, Stähli M, Kocher HP, Then RL. N-terminal amino acid sequence of the chromosomal dihydrofolate reductase purified from trimethoprim-resistant Staphylococcus aureus. FEBS Lett 1988; 242:157-60. [PMID: 3060373 DOI: 10.1016/0014-5793(88)81006-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The existence of two distinct dihydrofolate reductases (DHFR) in highly trimethoprim-resistant clinical isolates has been unequivocally demonstrated. The enzymes have been characterized with regard to the affinity for substrates and sensitivity to inhibitors. The chromosomal, trimethoprim-sensitive DHFR was purified to homogeneity by a new simple two-step procedure. Its N-terminal amino acid sequence, determined up to the first 35 amino acids, showed 69% homology with the Escherichia coli DHFR.
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Affiliation(s)
- P G Hartman
- Pharmaceutical Research Department, F. Hoffmann-La Roche & Co. Ltd, Basel, Switzerland
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31
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Thillet J, Absil J, Stone SR, Pictet R. Site-directed mutagenesis of mouse dihydrofolate reductase. Mutants with increased resistance to methotrexate and trimethoprim. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)37783-4] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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32
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Penner MH, Frieden C. Kinetic analysis of the mechanism of Escherichia coli dihydrofolate reductase. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(18)47675-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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33
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Czaplinsky KH, Kansy M, Seydel JK, Haller R. Design of a New Substituted 2,4-Diamino-5-benzylpyrimidine as Inhibitor of Bacterial Dihydrofolate Reductase Assisted by Molecular Graphics. ACTA ACUST UNITED AC 1987. [DOI: 10.1002/qsar.19870060206] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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34
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Sirawaraporn W, Yuthavong Y. Potentiating effect of pyrimethamine and sulfadoxine against dihydrofolate reductase from pyrimethamine-sensitive and pyrimethamine-resistant Plasmodium chabaudi. Antimicrob Agents Chemother 1986; 29:899-905. [PMID: 3729346 PMCID: PMC284175 DOI: 10.1128/aac.29.5.899] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Dihydrofolate reductase was partially purified from a pyrimethamine-sensitive Plasmodium chabaudi clone and a pyrimethamine-resistant clone derived from it and used in a study of the inhibitory effect of pyrimethamine and sulfadoxine, both alone and in combination. Kinetic analysis of the inhibitory effect of sulfadoxine against the enzyme from pyrimethamine-sensitive and -resistant parasites revealed that the drug inhibited the former enzyme competitively, with an inhibition constant (Kis) of 0.7 +/- 0.4 mM, but inhibited the latter enzyme noncompetitively, with Kis and Kii of 8.9 +/- 1.2 and 4.1 +/- 1.2 mM, respectively. Previous studies also showed competitive inhibition by pyrimethamine on the former enzyme and noncompetitive inhibition on the latter enzyme, with some 200-fold-lower affinity. Sulfadoxine and pyrimethamine exhibited a mutually potentiating effect on the enzyme activity, as revealed by the concave isoboles and the fractional inhibitions of less than unity. A potentiating effect was observed for the enzymes from both sources and was not dependent on the degree of the purification of the enzyme. Our results can be explained by assuming simultaneous binding of two inhibitors on the enzyme.
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35
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Al-Rubeai M, Dale JW. Purification and characterization of dihydrofolate reductase from Mycobacterium phlei. Biochem J 1986; 235:301-3. [PMID: 3741386 PMCID: PMC1146682 DOI: 10.1042/bj2350301] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The dihydrofolate reductase from Mycobacterium phlei was purified and characterized; it has an Mr of 15 000 and a pI of 4.8. It is competitively inhibited by both methotrexate and trimethoprim, although the affinity is less than for other bacterial dihydrofolate reductases.
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36
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Stone SR, Morrison JF. Mechanism of inhibition of dihydrofolate reductases from bacterial and vertebrate sources by various classes of folate analogues. BIOCHIMICA ET BIOPHYSICA ACTA 1986; 869:275-85. [PMID: 3511964 DOI: 10.1016/0167-4838(86)90067-1] [Citation(s) in RCA: 67] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Different classes of folate analogues have been examined with respect to the mechanism of their inhibition of dihydrofolate reductases from Escherichia coli and chicken liver. In addition, the degree of synergism between the binding of these compounds and NADPH has been investigated. Methotrexate acts as a slow, tight-binding inhibitor of both enzymes whereas trimethoprim is a slow, tight-binding inhibitor of the enzyme from E. coli and a classical inhibitor of the chicken-liver enzyme. Pyrimethamine, 2,4-diamino-6,7-dimethylpteridine, a phenyltriazine, folate and folinate exhibit classical inhibition. The degree of synergism between the binding of NADPH and the inhibitor varied from low for pyrimethamine and folate to very large for the phenyltriazine which binds to the chicken-liver enzyme almost 50 000-times more tightly in the presence of NADPH. The degree of synergism is reflected in the type of inhibition that the folate analogues yield with respect to NADPH. Compounds which exhibit slight synergism give noncompetitive inhibition whereas those with a high degree of synergism yield uncompetitive inhibition. With the exception of folinate, all compounds that act as classical inhibitors give rise to competitive inhibition with respect to dihydrofolate. Folinate exhibits competitive inhibition against NADPH and noncompetitive inhibition against dihydrofolate. These results are consistent with the formation of an enzyme-dihydrofolate-folinate complex. The (6S, alphaS)-diastereoisomer of folinate was bound at least 1000-times more tightly than the (6R, alphaS)-diastereoisomer. Consideration has been given to the possible interactions that occur between residues on the enzyme and groups on the inhibitor that give rise to slow-binding inhibition.
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37
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Burman LG. The antimicrobial activities of trimethoprim and sulfonamides. SCANDINAVIAN JOURNAL OF INFECTIOUS DISEASES 1986; 18:3-13. [PMID: 3515508 DOI: 10.3109/00365548609032299] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The folate inhibitor trimethoprim (TMP) is active against and potentially cidal to a few higher microorganisms and a wide spectrum of pathogenic bacteria except for Bacteroides, Branhamella, Brucella, Chlamydia, Clostridium, Mycobacterium, Mycoplasma, Nocardia, Neisseria, Pseudomonas and Treponema. These organisms tend to be more sensitive to sulfonamides (SUL) than to TMP, whereas TMP is 10- to 100-fold more active than SUL against most other bacteria. Synergy between TMP and SUL occurs at drug concentrations equal to or less than their respective MICs and is often seen in vitro with isolates that are sensitive or moderately resistant to one or both of the components. Synergy occurs over a wide range of ratios between TMP and SUL, the optimal being that between their respective MICs when acting singly. In vitro synergy is more impaired by bacterial resistance than by suboptimal TMP:SUL ratios. The vast majority of clinical isolates of Haemophilus, staphylococci, streptococci and enteric bacteria are inhibited in vitro by the minimum concentrations of drug attained in plasma during therapy. Exceptions are found among Enterobacter, Citrobacter, Serratia, Proteus and in particular Klebsiella where SUL resistance is common and isolates with TMP MICs of 5 mg/l or more may occur and lead to failure of TMP-SUL therapy in systemic infections. In the urinary tract drug concentrations that are synergistic and therefore inhibitory in vitro against isolates moderately resistant to SUL (MIC less than or equal to 1 g/l) and/or TMP (MIC less than or equal to 0.1 g/l) are present during TMP-SUL therapy. However, whether the synergy and the bactericidal effect of TMP-SUL observed in vitro play a role in vivo is controversial.
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38
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Penner MH, Frieden C. Substrate-induced hysteresis in the activity of Escherichia coli dihydrofolate reductase. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)89030-5] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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39
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Abstract
Antimicrobial combinations are used most frequently to provide broad-spectrum coverage; however, they are also frequently employed to enhance antimicrobial activity (synergism). Although there is extensive in vitro documentation of synergism for many antibiotic combinations, a clear advantage for these combinations has been difficult to demonstrate in clinical studies. Several types of combinations have been useful in clinical medicine and frequently result in synergism. These include combinations of a cell wall-active agent with an aminoglycosidic aminocyclitol, combinations of a beta-lactamase inhibitor with a beta-lactam, and combinations of agents that inhibit sequential steps in a metabolic pathway. Given its spectrum of activity, aztreonam will often be used with clindamycin or a beta-lactam antibiotic. Combinations of beta-lactams may be synergistic via several mechanisms. However, these combinations also exhibit significant potential for antagonism when used against gram-negative bacilli and, therefore, require careful evaluation prior to clinical use.
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40
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Baccanari DP, Tansik RL. Kinetics of methotrexate binding to dihydrofolate reductase from Neisseria gonorrhoeae. Biochem Pharmacol 1984; 33:2101-7. [PMID: 6430300 DOI: 10.1016/0006-2952(84)90579-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The kinetics of methotrexate inhibition of dihydrofolate reductase from Neisseria gonorrhoeae have been investigated. Methotrexate was shown to be a tight-binding inhibitor (Kt = 13 pM) competitive with dihydrofolate. However, "stoichiometric" or "pseudoirreversible" inhibition could not be demonstrated. Progress curves of inhibited assays quickly attained steady state regardless of the order of substrate addition, indicating that methotrexate association and dissociation processes were rapid. Kinetic techniques were used to measure the rate of methotrexate dissociation from the enzyme-NADPH-methotrexate ternary complex. At 30 degrees, the first-order off-rate constant (koff) was calculated to be 0.56 min-1. This value is approximately 40-fold greater than the dissociation rate constant of methotrexate for Escherichia coli dihydrofolate reductase. At lower temperatures, progress curves of methotrexate-inhibited gonococcal enzyme assays displayed marked increases in both curvature and the time to reach steady state. At 9 degrees, the methotrexate dissociation rate was slow enough (koff = 0.04 min-1) so that initial velocities of the reaction could be measured, and under these conditions methotrexate inhibition was shown to be "stoichiometric".
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41
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Joyner SS, Fling ME, Stone D, Baccanari DP. Characterization of an R-plasmid dihydrofolate reductase with a monomeric structure. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(18)91094-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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42
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Villafranca JE, Howell EE, Voet DH, Strobel MS, Ogden RC, Abelson JN, Kraut J. Directed mutagenesis of dihydrofolate reductase. Science 1983; 222:782-8. [PMID: 6356360 DOI: 10.1126/science.6356360] [Citation(s) in RCA: 165] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Three mutations of the enzyme dihydrofolate reductase were constructed by oligonucleotide-directed mutagenesis of the cloned Escherichia coli gene. The mutations--at residue 27, aspartic acid replaced with asparagine; at residue 39, proline replaced with cysteine; and at residue 95, glycine replaced with alanine--were designed to answer questions about the relations between molecular structure and function that were raised by the x-ray crystal structures. Properties of the mutant proteins show that Asp-27 is important for catalysis and that perturbation of the local structure at a conserved cis peptide bond following Gly-95 abolishes activity. Substitution of cysteine for proline at residue 39 results in the appearance of new forms of the enzyme that correspond to various oxidation states of the cysteine. One of these forms probably represents a species cross-linked by an intrachain disulfide bridge between the cysteine at position 85 and the new cysteine at position 39.
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Novak P, Stone D, Burchall JJ. R plasmid dihydrofolate reductase with a dimeric subunit structure. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(17)44369-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Smith SL, Burchall JJ. Alpha-pyridine nucleotides as substrates for a plasmid-specified dihydrofolate reductase. Proc Natl Acad Sci U S A 1983; 80:4619-23. [PMID: 6410395 PMCID: PMC384095 DOI: 10.1073/pnas.80.15.4619] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The alpha epimers of pyridine nucleotides are almost totally inactive as reductants in dehydrogenase reactions. In contrast, the R plasmid R67-specified dihydrofolate reductase (5,6,7,8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) isolated from trimethoprim-resistant Escherichia coli utilized alpha-NADPH and alpha-NADH in addition to the "normal" beta-epimers. The enzymes from bacterial and mammalian sources used only beta-NADPH and beta-NADH. THe Km value for alpha-NADPH (16 microM) was 4-fold greater than that for beta-NADPH (4 microM), while the maximal velocity of the alpha-NADPH-catalyzed reaction was 70% of that seen with the beta-NADPH. beta-NADP+ and alpha-NADP+ were competitive inhibitors of the R67 enzyme. Pyridine nucleotide analogues such as deamino- and acetyl-NADPH were used readily by bacterial, plasmid, and mammalian enzymes, whereas thio-NADPH was used only by the plasmid enzyme. These data suggest that the enzyme from R plasmid R67 possesses a pyridine nucleotide binding site different from that of other dihydrofolate reductases and dehydrogenases.
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Fling ME, Walton L, Elwell LP. Monitoring of plasmid-encoded, trimethoprim-resistant dihydrofolate reductase genes: detection of a new resistant enzyme. Antimicrob Agents Chemother 1982; 22:882-8. [PMID: 7181492 PMCID: PMC185675 DOI: 10.1128/aac.22.5.882] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Using-gene-specific radiolabeled probe DNAs, we analyzed 42 clinical bacterial isolates with high-level trimethoprim (Tp) resistance for the presence of a type I or a type II plasmid-specified dihydrofolate reductase (DHFR) gene. Plasmid DNA from 17 strains harbored a type I DHFR, whereas 11 isolates contained plasmids that harbored a type II DHFR structural gene. The plasmid DNAs from five strains appeared to hybridize with both type I and type II DHFR probe DNAs. In addition, eight isolates had type I resistance determinants integrated into the chromosomes, presumably on transposon 7 (Tn7). Among the strains analyzed in this survey, none of the chromosomally located, Tp-insensitive reductases were of the type II class. Both the plasmid and chromosomal DNAs of one isolate showed no homology with either the type I or type II DHFR probe DNA. The plasmid harbored by this strain encoded a "new" Tp-resistant enzyme that differed significantly, both in molecular weight and with respect to trimethoprim and methotrexate inhibition kinetics, from the previously characterized plasmid-associated dihydrofolate reductases.
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Baccanari DP, Daluge S, King RW. Inhibition of dihydrofolate reductase: effect of reduced nicotinamide adenine dinucleotide phosphate on the selectivity and affinity of diaminobenzylpyrimidines. Biochemistry 1982; 21:5068-75. [PMID: 6814484 DOI: 10.1021/bi00263a034] [Citation(s) in RCA: 76] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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Holmes PF, Liehr JG, Henkin J. Synthesis and characterization of 2′-azidoaminopterin as a potential photoaffinity label for folate-utilizing enzymes. Bioorg Chem 1982. [DOI: 10.1016/0045-2068(82)90004-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Roth B, Cheng CC. Recent progress in the medicinal chemistry of 2,4-diaminopyrimidines. PROGRESS IN MEDICINAL CHEMISTRY 1982; 19:269-331. [PMID: 6129679 DOI: 10.1016/s0079-6468(08)70332-1] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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