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Li Y, Zhang R, Xu Y. Structure-based mechanisms: On the way to apply alcohol dehydrogenases/reductases to organic-aqueous systems. Int J Biol Macromol 2020; 168:412-427. [PMID: 33316337 DOI: 10.1016/j.ijbiomac.2020.12.068] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2020] [Revised: 12/08/2020] [Accepted: 12/08/2020] [Indexed: 12/20/2022]
Abstract
Alcohol dehydrogenases/reductases catalyze enantioselective syntheses of versatile chiral compounds relying on direct hydride transfer from cofactor to substrates, or to an intermediate and then to substrates. Since most of the substrates catalyzed by alcohol dehydrogenases/reductases are insoluble in aqueous solutions, increasing interest has been turning to organic-aqueous systems. However, alcohol dehydrogenases/reductases are normally instable in organic solvents, leading to the unsatisfied enantioselective synthesis efficiency. The behaviors of these enzymes in organic solvents at an atomic level are unclear, thus it is of great importance to understand its structure-based mechanisms in organic-aqueous systems to improve their relative stability. Here, we summarized the accessible structures of alcohol dehydrogenases/reductases in Protein Data Bank crystallized in organic-aqueous systems, and compared the structures of alcohol dehydrogenases/reductases which have different tolerance towards organic solvents. By understanding the catalytic behaviors and mechanisms of these enzymes in organic-aqueous systems, the efficient enantioselective syntheses mediated by alcohol dehydrogenases/reductases and further challenges are also discussed through solvent engineering and enzyme-immobilization in the last decade.
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Affiliation(s)
- Yaohui Li
- Key Laboratory of Industrial Biotechnology of Ministry of Education & School of Biotechnology, Jiangnan University, Wuxi 214122, PR China; Department of Biological Science, Columbia University, New York, NY 10025, United States
| | - Rongzhen Zhang
- Key Laboratory of Industrial Biotechnology of Ministry of Education & School of Biotechnology, Jiangnan University, Wuxi 214122, PR China.
| | - Yan Xu
- Key Laboratory of Industrial Biotechnology of Ministry of Education & School of Biotechnology, Jiangnan University, Wuxi 214122, PR China.
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2
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Wong HE, Pack SP, Kwon I. Positional effects of hydrophobic non-natural amino acid mutagenesis into the surface region of murine dihydrofolate reductase on enzyme properties. Biochem Eng J 2016. [DOI: 10.1016/j.bej.2015.12.014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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3
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Liu CT, Francis K, Layfield JP, Huang X, Hammes-Schiffer S, Kohen A, Benkovic SJ. Escherichia coli dihydrofolate reductase catalyzed proton and hydride transfers: temporal order and the roles of Asp27 and Tyr100. Proc Natl Acad Sci U S A 2014; 111:18231-6. [PMID: 25453098 PMCID: PMC4280594 DOI: 10.1073/pnas.1415940111] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The reaction catalyzed by Escherichia coli dihydrofolate reductase (ecDHFR) has become a model for understanding enzyme catalysis, and yet several details of its mechanism are still unresolved. Specifically, the mechanism of the chemical step, the hydride transfer reaction, is not fully resolved. We found, unexpectedly, the presence of two reactive ternary complexes [enzyme:NADPH:7,8-dihydrofolate (E:NADPH:DHF)] separated by one ionization event. Furthermore, multiple kinetic isotope effect (KIE) studies revealed a stepwise mechanism in which protonation of the DHF precedes the hydride transfer from the nicotinamide cofactor (NADPH) for both reactive ternary complexes of the WT enzyme. This mechanism was supported by the pH- and temperature-independent intrinsic KIEs for the C-H→C hydride transfer between NADPH and the preprotonated DHF. Moreover, we showed that active site residues D27 and Y100 play a synergistic role in facilitating both the proton transfer and subsequent hydride transfer steps. Although D27 appears to have a greater effect on the overall rate of conversion of DHF to tetrahydrofolate, Y100 plays an important electrostatic role in modulating the pKa of the N5 of DHF to enable the preprotonation of DHF by an active site water molecule.
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Affiliation(s)
- C Tony Liu
- Department of Chemistry, Pennsylvania State University, University Park, PA 16802
| | - Kevin Francis
- Department of Chemistry, The University of Iowa, Iowa City, IA 52242; and
| | - Joshua P Layfield
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801-3364
| | - Xinyi Huang
- Department of Chemistry, Pennsylvania State University, University Park, PA 16802
| | - Sharon Hammes-Schiffer
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801-3364
| | - Amnon Kohen
- Department of Chemistry, The University of Iowa, Iowa City, IA 52242; and
| | - Stephen J Benkovic
- Department of Chemistry, Pennsylvania State University, University Park, PA 16802;
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4
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Timson MJ, Duff MR, Dickey G, Saxton AM, Reyes-De-Corcuera JI, Howell EE. Further studies on the role of water in R67 dihydrofolate reductase. Biochemistry 2013; 52:2118-27. [PMID: 23458706 DOI: 10.1021/bi301544k] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Previous osmotic pressure studies of two nonhomologous dihydrofolate reductase (DHFR) enzymes found tighter binding of the nicotinamide adenine dinucleotide phosphate cofactor upon addition of neutral osmolytes. This result is consistent with water release accompanying binding. In contrast, osmotic stress studies found weaker binding of the dihydrofolate (DHF) substrate for both type I and type II DHFRs in the presence of osmolytes; this observation can be explained if dihydrofolate interacts with osmolytes and shifts the equilibrium from the enzyme-bound state toward the unbound substrate. Nuclear magnetic resonance experiments support this hypothesis, finding that osmolytes interact with dihydrofolate. To consider binding without added osmolytes, a high-pressure approach was used. In this study, the type II enzyme, R67 DHFR, was subjected to high hydrostatic pressure (HHP). Both enzyme activity and fluorescence measurements find the protein tolerates pressures up to 200 MPa. Binding of the cofactor to R67 DHFR weakens with increasing pressure, and a positive association volume of 11.4 ± 0.5 cm(3)/mol was measured. Additionally, an activation volume of 3.3 ± 0.5 cm(3)/mol describing k(cat)/K(m(DHF)) was determined from progress curve analysis. Results from these HHP experiments suggest water release accompanies binding of both the cofactor and DHF to R67 DHFR. In an additional set of experiments, isothermal titration calorimetry studies in H2O and D2O find that water reorganization dominates the enthalpy associated with binding of DHF to R67 DHFR·NADP(+), while no obvious effects occur for cofactor binding. The combined results indicate that water plays an active role in ligand binding to R67 DHFR.
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Affiliation(s)
- Mary Jane Timson
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee , Knoxville, Tennessee 37996-0840, United States
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5
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Grubbs J, Rahmanian S, DeLuca A, Padmashali C, Jackson M, Duff MR, Howell EE. Thermodynamics and solvent effects on substrate and cofactor binding in Escherichia coli chromosomal dihydrofolate reductase. Biochemistry 2011; 50:3673-85. [PMID: 21462996 DOI: 10.1021/bi2002373] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Chromosomal dihydrofolate reductase from Escherichia coli catalyzes the reduction of dihydrofolate to tetrahydrofolate using NADPH as a cofactor. The thermodynamics of ligand binding were examined using an isothermal titration calorimetry approach. Using buffers with different heats of ionization, zero to a small, fractional proton release was observed for dihydrofolate binding, while a proton was released upon NADP(+) binding. The role of water in binding was additionally monitored using a number of different osmolytes. Binding of NADP(+) is accompanied by the net release of ∼5-24 water molecules, with a dependence on the identity of the osmolyte. In contrast, binding of dihydrofolate is weakened in the presence of osmolytes, consistent with "water uptake". Different effects are observed depending on the identity of the osmolyte. The net uptake of water upon dihydrofolate binding was previously observed in the nonhomologous R67-encoded dihydrofolate reductase (dfrB or type II enzyme) [Chopra, S., et al. (2008) J. Biol. Chem. 283, 4690-4698]. As R67 dihydrofolate reductase possesses a nonhomologous sequence and forms a tetrameric structure with a single active site pore, the observation of weaker DHF binding in the presence of osmolytes in both enzymes implicates cosolvent effects on free dihydrofolate. Consistent with this analysis, stopped flow experiments find betaine mostly affects DHF binding via changes in k(on), while betaine mostly affects NADPH binding via changes in k(off). Finally, nonadditive enthalpy terms when binary and ternary cofactor binding events are compared suggest the presence of long-lived conformational transitions that are not included in a simple thermodynamic cycle.
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Affiliation(s)
- Jordan Grubbs
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996-0840, USA
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6
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Böck RA, Soulages JL, Barrow WW. Substrate and inhibitor specificity of Mycobacterium avium dihydrofolate reductase. FEBS J 2007; 274:3286-98. [PMID: 17542991 DOI: 10.1111/j.1742-4658.2007.05855.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Dihydrofolate reductase (EC 1.5.1.3) is a key enzyme in the folate biosynthetic pathway. Information regarding key residues in the dihydrofolate-binding site of Mycobacterium avium dihydrofolate reductase is lacking. On the basis of previous information, Asp31 and Leu32 were selected as residues that are potentially important in interactions with dihydrofolate and antifolates (e.g. trimethoprim), respectively. Asp31 and Leu32 were modified by site-directed mutagenesis, giving the mutants D31A, D31E, D31Q, D31N and D31L, and L32A, L32F and L32D. Mutated proteins were expressed in Escherichia coli BL21(DE3)pLysS and purified using His-Bind resin; functionality was assessed in comparison with the recombinant wild type by a standard enzyme assay, and growth complementation and kinetic parameters were evaluated. All Asp31 substitutions affected enzyme function; D31E, D31Q and D31N reduced activity by 80-90%, and D31A and D31L by > 90%. All D31 mutants had modified kinetics, ranging from three-fold (D31N) to 283-fold (D31L) increases in K(m) for dihydrofolate, and 12-fold (D31N) to 223 077-fold (D31L) decreases in k(cat)/K(m). Of the Leu32 substitutions, only L32D caused reduced enzyme activity (67%) and kinetic differences from the wild type (seven-fold increase in K(m); 21-fold decrease in k(cat)/K(m)). Only minor variations in the K(m) for NADPH were observed for all substitutions. Whereas the L32F mutant retained similar trimethoprim affinity as the wild type, the L32A mutation resulted in a 12-fold decrease in affinity and the L32D mutation resulted in a seven-fold increase in affinity for trimethoprim. These findings support the hypotheses that Asp31 plays a functional role in binding of the substrate and Leu32 plays a functional role in binding of trimethoprim.
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Affiliation(s)
- Ronnie A Böck
- Department of Veterinary Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK 74078, USA
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7
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Khavrutskii IV, Price DJ, Lee J, Brooks CL. Conformational change of the methionine 20 loop of Escherichia coli dihydrofolate reductase modulates pKa of the bound dihydrofolate. Protein Sci 2007; 16:1087-100. [PMID: 17473015 PMCID: PMC2206655 DOI: 10.1110/ps.062724307] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2006] [Revised: 03/05/2007] [Accepted: 03/06/2007] [Indexed: 10/23/2022]
Abstract
We evaluate the pK(a) of dihydrofolate (H(2)F) at the N(5) position in three ternary complexes with Escherichia coli dihydrofolate reductase (ecDHFR), namely ecDHFR(NADP(+):H(2)F) in the closed form (1), and the Michaelis complexes ecDHFR(NADPH:H(2)F) in the closed (2) and occluded (3) forms, by performing free energy perturbation with molecular dynamics simulations (FEP/MD). Our simulations suggest that in the Michaelis complex the pK(a) is modulated by the Met20 loop fluctuations, providing the largest pK(a) shift in substates with a "tightly closed" loop conformation; in the "partially closed/open" substates, the pK(a) is similar to that in the occluded complex. Conducive to the protonation, tightly closing the Met20 loop enhances the interactions of the cofactor and the substrate with the Met20 side chain and aligns the nicotinamide ring of the cofactor coplanar with the pterin ring of the substrate. Overall, the present study favors the hypothesis that N(5) is protonated directly from solution and provides further insights into the mechanism of the substrate protonation.
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Affiliation(s)
- Ilja V Khavrutskii
- The Scripps Research Institute, Department of Molecular Biology, TPC6, La Jolla, California 92037, USA
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8
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Hicks SN, Smiley RD, Stinnett LG, Minor KH, Howell EE. Role of Lys-32 residues in R67 dihydrofolate reductase probed by asymmetric mutations. J Biol Chem 2004; 279:46995-7002. [PMID: 15333636 DOI: 10.1074/jbc.m404484200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
R67 dihydrofolate reductase (R67 DHFR) is a novel protein encoded by an R-plasmid that confers resistance to the antibiotic, trimethoprim. This homotetrameric enzyme possesses 222 symmetry, which imposes numerous constraints on the single active site pore, including a "one-site-fits-both" strategy for binding its ligands, dihydrofolate (DHF) and NADPH. Previous studies uncovered salt effects on binding and catalysis (Hicks, S. N., Smiley, R. D., Hamilton, J. B., and Howell, E. E. (2003) Biochemistry 42, 10569-10578), however the one or more residues that participate in ionic contacts with the negatively charged tail of DHF as well as the phosphate groups in NADPH were not identified. Several studies predict that Lys-32 residues were involved, however mutations at this residue destabilize the R67 DHFR homotetramer. To study the role of Lys-32 in binding and catalysis, asymmetric K32M mutations have been utilized. To create asymmetry, individual mutations were added to a tandem array of four in-frame gene copies. These studies show one K32M mutation is tolerated quite well, whereas addition of two mutations has variable effects. Two double mutants, K32M:1+2 and K32M: 1+4, which place the mutations on opposite sides of the pore, reduce kcat. However a third double mutant, K32M: 1+3, that places two mutations on the same half pore, enhances kcat 4- to 5-fold compared with the parent enzyme, albeit at the expense of weaker binding of ligands. Because the kcat/Km values for this double mutant series are similar, these mutations appear to have uncovered some degree of non-productive binding. This non-productive binding mode likely arises from formation of an ionic interaction that must be broken to allow access to the transition state. The K32M:1+3 mutant data suggest this interaction is an ionic interaction between Lys-32 and the charged tail of dihydrofolate. This unusual catalytic scenario arises from the 222 symmetry imposed on the single active site pore.
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Affiliation(s)
- Stephanie N Hicks
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996-0840, USA
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9
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Rod TH, Radkiewicz JL, Brooks CL. Correlated motion and the effect of distal mutations in dihydrofolate reductase. Proc Natl Acad Sci U S A 2003; 100:6980-5. [PMID: 12756296 PMCID: PMC165816 DOI: 10.1073/pnas.1230801100] [Citation(s) in RCA: 190] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2003] [Indexed: 11/18/2022] Open
Abstract
Dihydrofolate reductase (DHFR) catalyzes the reduction of dihydrofolate to tetrahydrofolate. The catalytic rate in this system has been found to be significantly affected by mutations far from the site of chemical activity in the enzyme [Rajagopalan, P. T. R, Lutz, S., and Benkovic, S. J. (2002) Biochemistry 41, 12618-12628]. On the basis of extensive computer simulations for wild-type DHFR from Escherichia coli and four mutants (G121S, G121V, M42F, and M42F/G121S), we show that key parameters for catalysis are changed. The parameters we study are relative populations of different conformations sampled and hydrogen bonds. We find that the mutations result in long-range structural perturbations, rationalizing the effects that the mutations have on the kinetics of the enzyme. Such perturbations also provide a rationalization for the reported nonadditivity effect for double mutations. We finally examine the role a structural perturbation will have on the hydride transfer step. On the basis of our new findings, we discuss the role of coupled motions between distant regions in the enzyme, which previously was reported by Radkiewicz and Brooks.
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Affiliation(s)
- Thomas H Rod
- Department of Molecular Biology, The Scripps Research Institute, TPC6, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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10
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Sirawaraporn W, Sirawaraporn R, Yongkiettrakul S, Anuwatwora A, Rastelli G, Kamchonwongpaisan S, Yuthavong Y. Mutational analysis of Plasmodium falciparum dihydrofolate reductase: the role of aspartate 54 and phenylalanine 223 on catalytic activity and antifolate binding. Mol Biochem Parasitol 2002; 121:185-93. [PMID: 12034452 DOI: 10.1016/s0166-6851(02)00035-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The catalytic activity and ability to confer resistance to antifolates of Plasmodium falciparum dihydrofolate reductase (pfDHFR) through single and double mutations at Asp-54 and Phe-223 were investigated. A single Asp54Glu (D54E) mutation in the pfDHFR domain greatly decreased the catalytic activity of the enzyme and affected both the K(m) values for the substrate dihydrofolate and the K(i) values for pyrimethamine, cycloguanil and WR99210. The Phe223Ser (F223S) single mutant had unperturbed kinetics but had very poor affinity with the first two antifolates. The ability to confer high resistance to the antifolates of F223S enzyme was, however, abolished in the D54E+F223S double mutant enzyme. When D54E mutation was present together with the A16V+S108T double mutation, the effects on the K(m) values for the substrate dihydrofolate and the binding affinity of antifolates were much more pronounced. The severely impaired kinetics and poor activity observed in A16V+S108T+D54E enzyme could, however, be restored when F223S was introduced, while the binding affinities to the antifolates remained poor. The experimental findings can be explained with a model for substrate and inhibitor binding. Our data not only indicate the importance of Asp-54 of pfDHFR in catalysis and inhibitor binding, but also provide evidence that infer the potentially crucial function of the C-terminal portion of pfDHFR domain.
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Affiliation(s)
- Worachart Sirawaraporn
- Department of Biochemistry, Faculty of Science, Mahidol University, Rama 6 Rd., 10400, Bangkok 10400, Thailand.
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11
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Karginov VA, Mamaev SV, An H, Van Cleve MD, Hecht SM, Komatsoulis GA, Abelson JN. Probing the Role of an Active Site Aspartic Acid in Dihydrofolate Reductase. J Am Chem Soc 1997. [DOI: 10.1021/ja971099l] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Vladimir A. Karginov
- Contribution from the Departments of Chemistry and Biology, University of Virginia, Charlottesville, Virginia, 22901, and Division of Biology, California Institute of Technology, Pasadena, California, 91125
| | - Sergey V. Mamaev
- Contribution from the Departments of Chemistry and Biology, University of Virginia, Charlottesville, Virginia, 22901, and Division of Biology, California Institute of Technology, Pasadena, California, 91125
| | - Haoyun An
- Contribution from the Departments of Chemistry and Biology, University of Virginia, Charlottesville, Virginia, 22901, and Division of Biology, California Institute of Technology, Pasadena, California, 91125
| | - Mark D. Van Cleve
- Contribution from the Departments of Chemistry and Biology, University of Virginia, Charlottesville, Virginia, 22901, and Division of Biology, California Institute of Technology, Pasadena, California, 91125
| | - Sidney M. Hecht
- Contribution from the Departments of Chemistry and Biology, University of Virginia, Charlottesville, Virginia, 22901, and Division of Biology, California Institute of Technology, Pasadena, California, 91125
| | - George A. Komatsoulis
- Contribution from the Departments of Chemistry and Biology, University of Virginia, Charlottesville, Virginia, 22901, and Division of Biology, California Institute of Technology, Pasadena, California, 91125
| | - John N. Abelson
- Contribution from the Departments of Chemistry and Biology, University of Virginia, Charlottesville, Virginia, 22901, and Division of Biology, California Institute of Technology, Pasadena, California, 91125
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12
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Cannon WR, Garrison BJ, Benkovic SJ. Consideration of the pH-dependent inhibition of dihydrofolate reductase by methotrexate. J Mol Biol 1997; 271:656-68. [PMID: 9281432 DOI: 10.1006/jmbi.1997.1173] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Poisson-Boltzmann calculations were used to determine the pKa of protein functional groups in the unliganded dihydrofolate reductase enzyme, and the pKa of protein and ligand groups in methotrexate-enzyme complexes. The results reported here are in conflict with two fundamental tenets of dihydrofolate reductase inhibition by methotrexate: (1) Asp27 is not expected to be protonated near pH 6.5 in the apoenzyme as previously proposed based on fitting of empirical equations to binding data, and (2) the calculated pKa for the pteridine N1 of the inhibitor while bound to the protein is significantly lower than that estimated for this group from interpretation of NMR data (>10). In fact, the electrostatic calculations and complementary quantum chemical calculations indicate that Asp27 is likely protonated when methotrexate is bound, resulting in a neutral dipole-dipole interaction rather than a salt-bridge between the enzyme and the inhibitor. Reasons for this discrepancy with the experimental data are discussed. Furthermore, His45 and Glu17 in the Escherichia coli enzyme are proposed to be in part responsible for the pH dependence of the conformational degeneracy in the inhibitor-enzyme complex.
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Affiliation(s)
- W R Cannon
- Department of Chemistry 152 Davey Laboratory, Pennsylvania State University, University Park, PA 16802, USA
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13
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Zhuang P, Yin M, Holland J, Peterson C, Howell E. Artificial duplication of the R67 dihydrofolate reductase gene to create protein asymmetry. Effects on protein activity and folding. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)41580-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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14
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Dion A, Linn CE, Bradrick TD, Georghiou S, Howell EE. How do mutations at phenylalanine-153 and isoleucine-155 partially suppress the effects of the aspartate-27-->serine mutation in Escherichia coli dihydrofolate reductase? Biochemistry 1993; 32:3479-87. [PMID: 8461309 DOI: 10.1021/bi00064a036] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Several second-site suppressors of the D27S lesion in Escherichia coli dihydrofolate reductase (DHFR) have been identified. The activity of the primary mutant, D27S DHRF, was found to be greatly decreased at pH 7.0, consistent with aspartic acid-27 being critically involved in proton donation during catalysis. Partial suppressors of the D27S mutation have been selected by their ability to confer an increased resistance to trimethoprim upon host E. coli; the suppressors have been identified as F153S or I155N substitutions. D27S+F153S and D27S+I155N DHFRs display 2-3-fold increases in kcat over D27S DHFR values, but only the F153S mutation decreases the Km for dihydrofolate by a factor of 2. Neither double mutant approaches wild-type DHFR activity. Unexpectedly, Phe153 and Ile155 occur on the surface of the protein and are approximately 8 and 14 A distant from the active site. Ile155 is a member of a beta-bulge. A previously identified suppressing mutation, F137S, occurs nearby and is also a member of the same beta-bulge [Howell et al. (1990) Biochemistry 29, 8561-8569]. Clustering of these three second-site mutations indicates this area of the structure may be important in protein function. Conformational changes due to the presence of these suppressing mutations are likely as the F153S and I155N mutations do not affect hydride-transfer rates upon introduction in wild-type DHFR and alterations in circular dichroism spectra are associated with the double-mutant DHFRs.
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Affiliation(s)
- A Dion
- Department of Biochemistry, University of Tennessee, Knoxville 37996-0840
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15
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Ahrweiler PM, Frieden C. Effects of point mutations in a hinge region on the stability, folding, and enzymatic activity of Escherichia coli dihydrofolate reductase. Biochemistry 1991; 30:7801-9. [PMID: 1868058 DOI: 10.1021/bi00245a020] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The role of a hinge region in the folding, stability, and activity of Escherichia coli dihydrofolate reductase was investigated with three site-directed mutants at valine-88, the central residue of the hinge. The three mutants, V88A and V88I and a valine-88 deletion, were created to perturb the packing of hydrophobic residues in the interior of a loose turn formed by residues 85-91. Deleting the valine-88 residue destabilized the protein by 2.93 +/- 0.6 kcal/mol as determined by equilibrium unfolding transitions in urea monitored by circular dichroism at 20 degrees C. Substitution of alanine for valine-88 stabilized the protein by -0.20 +/- 0.02 kcal/mol, and the isoleucine substitution was mildly destabilizing by 1.73 +/- 0.2 kcal/mol. Although there was no clear correlation between side-chain volume and stability, these results suggest that side-chain interactions in the interior of the turn influence the folding and stability of dihydrofolate reductase. The specific activity of the valine deletion mutant was approximately twice that of the wild-type protein while the specific activities of the V88A and V88I proteins were only slightly greater than the wild type. The full time courses of the reactions catalyzed by the mutants were almost identical with that for the wild type, indicating no major changes in the kinetic mechanism. Additionally, the rate constants associated with interconversion between various forms of the apoenzyme were identical for the mutant and wild-type enzymes. The rate constants for refolding transitions were examined by dilution of urea-inactivated protein.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- P M Ahrweiler
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110
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