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Hua J, Tran T, Chien J, Trimmer EE. Kinetic Characterization of
Escherichia coli
Mutant Methylenetetrahydrofolate Reductase Flavoenzymes Leu277Ala and Leu277Ile. FASEB J 2020. [DOI: 10.1096/fasebj.2020.34.s1.06708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Du S, Tetrick MG, Li R, Chien J, Trimmer EE. Kinetic Characterization of Mutant Methylenetetrahydrofolate Reductase Enzymes His273Ala and His273Gln. FASEB J 2020. [DOI: 10.1096/fasebj.2020.34.s1.03502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Zuo C, Jolly AL, Nikolova AP, Satzer DI, Cao S, Sanchez JS, Ballou DP, Trimmer EE. A role for glutamine 183 in the folate oxidative half-reaction of methylenetetrahydrofolate reductase from Escherichia coli. Arch Biochem Biophys 2018; 642:63-74. [PMID: 29407039 DOI: 10.1016/j.abb.2018.01.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2017] [Revised: 01/01/2018] [Accepted: 01/22/2018] [Indexed: 10/18/2022]
Abstract
The flavoprotein methylenetetrahydrofolate reductase (MTHFR) from Escherichia coli catalyzes a ping-pong reaction with NADH and 5,10-methylenetetrahydrofolate (CH2-H4folate) to produce NAD+ and 5-methyltetrahydrofolate (CH3-H4folate). This work focuses on the function of the invariant, active-site aminoacyl residue Gln183. X-ray structures of the enzyme complexes Ered(wild-type)•NADH and Eox(Glu28Gln)•CH3-H4folate indicate that Gln183 makes key hydrogen-bonding interactions with both NADH and folate in their respective half-reactions, suggesting roles in binding each substrate. We propose that the polarity of Gln183 may also aid in stabilizing the proposed 5-iminium cation intermediate during catalysis in the oxidative half-reaction with folate. We have prepared mutants Gln183Ala and Gln183Glu, which we hypothesize to have altered charge/polarity and hydrogen bonding properties. We have examined the enzymes by steady-state and stopped-flow kinetics and by measurement of the flavin redox potentials. In the reductive half-reaction, NADH binding affinity and the rate of flavin reduction have not been hindered by either mutation. By contrast, our results support a minor role for Gln183 in the oxidative half-reaction. The Gln183Ala variant exhibited a 6-10 fold lower rate of folate reduction and bound CH2-H4folate with 7-fold lower affinity, whereas the Gln183Glu mutant displayed catalytic constants within 3-fold of the wild-type enzyme.
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Affiliation(s)
- Chong Zuo
- Department of Chemistry, Grinnell College, Grinnell, IA 50112, USA
| | - Amber L Jolly
- Department of Chemistry, Grinnell College, Grinnell, IA 50112, USA
| | | | - David I Satzer
- Department of Chemistry, Grinnell College, Grinnell, IA 50112, USA
| | - Sirui Cao
- Department of Chemistry, Grinnell College, Grinnell, IA 50112, USA
| | - Jeremy S Sanchez
- Department of Chemistry, Grinnell College, Grinnell, IA 50112, USA
| | - David P Ballou
- Department of Biological Chemistry, The University of Michigan, Ann Arbor, MI 48109, USA
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Abstract
The flavoprotein d-amino acid oxidase has long served as a paradigm for understanding the mechanism of oxidation of amino acids by flavoproteins. Recently, a mutant d-amino acid oxidase (Y228L/R283G) that catalyzed the oxidation of amines rather than amino acids was described [Yasukawa, K., et al. (2014) Angew. Chem., Int. Ed. 53, 4428-4431]. We describe here the use of pH and kinetic isotope effects with (R)-α-methylbenzylamine as a substrate to determine whether the mutant enzyme utilizes the same catalytic mechanism as the wild-type enzyme. The effects of pH on the steady-state and rapid-reaction kinetics establish that the neutral amine is the substrate, while an active-site residue, likely Tyr224, must be uncharged for productive binding. There is no solvent isotope effect on the kcat/Km value for the amine, consistent with the neutral amine being the substrate. The deuterium isotope effect on the kcat/Km value is pH-independent, with an average value of 5.3, similar to values found with amino acids as substrates for the wild-type enzyme and establishing that there is no commitment to catalysis with this substrate. The kcat/KO2 value is similar to that seen with amino acids as the substrate, consistent with the oxidative half-reaction being unperturbed by the mutation and with flavin oxidation preceding product release. All of the data are consistent with the mutant enzyme utilizing the same mechanism as the wild-type enzyme, transfer of hydride from the neutral amine to the flavin.
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Affiliation(s)
- Elizabeth E Trimmer
- Department of Chemistry, Grinnell College , Grinnell, Iowa 50112, United States
| | - Udayanga S Wanninayake
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center , San Antonio, Texas 78229, United States
| | - Paul F Fitzpatrick
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center , San Antonio, Texas 78229, United States
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E. Trimmer E. Methylenetetrahydrofolate Reductase: Biochemical Characterization and Medical Significance. Curr Pharm Des 2013; 19:2574-93. [DOI: 10.2174/1381612811319140008] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Accepted: 10/30/2012] [Indexed: 11/22/2022]
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6
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Wang J, Trimmer EE. pH‐dependent Studies of
E. coli
Methylenetetrahydrofolate Reductase. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.756.13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Lee MN, Takawira D, Nikolova AP, Ballou DP, Furtado VC, Phung NL, Still BR, Thorstad MK, Tanner JJ, Trimmer EE. Functional role for the conformationally mobile phenylalanine 223 in the reaction of methylenetetrahydrofolate reductase from Escherichia coli. Biochemistry 2009; 48:7673-85. [PMID: 19610625 DOI: 10.1021/bi9007325] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The flavoprotein methylenetetrahydrofolate reductase from Escherichia coli catalyzes the reduction of 5,10-methylenetetrahydrofolate (CH(2)-H(4)folate) by NADH via a ping-pong reaction mechanism. Structures of the reduced enzyme in complex with NADH and of the oxidized Glu28Gln enzyme in complex with CH(3)-H(4)folate [Pejchal, R., Sargeant, R., and Ludwig, M. L. (2005) Biochemistry 44, 11447-11457] have revealed Phe223 as a conformationally mobile active site residue. In the NADH complex, the NADH adopts an unusual hairpin conformation and is wedged between the isoalloxazine ring of the FAD and the side chain of Phe223. In the folate complex, Phe223 swings out from its position in the NADH complex to stack against the p-aminobenzoate ring of the folate. Although Phe223 contacts each substrate in E. coli MTHFR, this residue is not invariant; for example, a leucine occurs at this site in the human enzyme. To examine the role of Phe223 in substrate binding and catalysis, we have constructed mutants Phe223Ala and Phe223Leu. As predicted, our results indicate that Phe223 participates in the binding of both substrates. The Phe223Ala mutation impairs NADH and CH(2)-H(4)folate binding each 40-fold yet slows catalysis of both half-reactions less than 2-fold. Affinity for CH(2)-H(4)folate is unaffected by the Phe223Leu mutation, and the variant catalyzes the oxidative half-reaction 3-fold faster than the wild-type enzyme. Structures of ligand-free Phe223Leu and Phe223Leu/Glu28Gln MTHFR in complex with CH(3)-H(4)folate have been determined at 1.65 and 1.70 A resolution, respectively. The structures show that the folate is bound in a catalytically competent conformation, and Leu223 undergoes a conformational change similar to that observed for Phe223 in the Glu28Gln-CH(3)-H(4)folate structure. Taken together, our results suggest that Leu may be a suitable replacement for Phe223 in the oxidative half-reaction of E. coli MTHFR.
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Affiliation(s)
- Moon N Lee
- Department of Chemistry, Grinnell College, Grinnell, Iowa 50112, USA
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Mohrig JR, Carlson HK, Coughlin JM, Hofmeister GE, McMartin LA, Rowley EG, Trimmer EE, Wild AJ, Schultz SC. Novel Syn Intramolecular Pathway in Base-Catalyzed 1,2-Elimination Reactions of β-Acetoxy Esters. J Org Chem 2007; 72:793-8. [PMID: 17253797 DOI: 10.1021/jo0619027] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
As part of a comprehensive investigation of electronic effects on the stereochemistry of base-catalyzed 1,2-elimination reactions, we observed a new syn intramolecular pathway in the elimination of acetic acid from beta-acetoxy esters and thioesters. 1H and 2H NMR investigation of reactions using stereospecifically labeled tert-butyl (2R*,3R*)-3-acetoxy-2,3-2H2-butanoate (1) and its (2R*,3S*) diastereomer (2) shows that 23 +/- 2% syn elimination occurs. The elimination reactions were catalyzed with KOH or (CH3)4NOH in ethanol/water under rigorously non-ion-pairing conditions. By contrast, the more sterically hindered beta-trimethylacetoxy ester produces only 6 +/- 1% syn elimination. These data strongly support an intramolecular (Ei) syn path for elimination of acetic acid, most likely through the oxyanion produced by nucleophilic attack at the carbonyl carbon of the beta-acetoxy group. The analogous thioesters, S-tert-butyl (2R*,3R*)-3-acetoxy-2,3-2H2-butanethioate (3) and its (2R*,3S*) diastereomer (4), showed 18 +/- 2% syn elimination, whereas the beta-trimethylacetoxy substrate gave 5 +/- 1% syn elimination. The more acidic thioester substrates do not produce an increased amount of syn stereoselectivity even though their elimination reactions are at the E1cb interface.
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Affiliation(s)
- Jerry R Mohrig
- Department of Chemistry, Carleton College, Northfield, Minnesota 55057, USA.
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Trimmer EE, Ballou DP, Galloway LJ, Scannell SA, Brinker DR, Casas KR. Aspartate 120 of Escherichia coli methylenetetrahydrofolate reductase: evidence for major roles in folate binding and catalysis and a minor role in flavin reactivity. Biochemistry 2005; 44:6809-22. [PMID: 15865426 DOI: 10.1021/bi0477236] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Escherichia coli methylenetetrahydrofolate reductase (MTHFR) catalyzes the NADH-linked reduction of 5,10-methylenetetrahydrofolate (CH(2)-H(4)folate) to 5-methyltetrahydrofolate (CH(3)-H(4)folate) using flavin adenine dinucleotide (FAD) as cofactor. MTHFR is unusual among flavin oxidoreductases because it contains a conserved, negatively rather than positively charged amino acid (aspartate 120) near the N1-C2=O position of the flavin. At this location, Asp 120 is expected to influence the redox properties of the enzyme-bound FAD. Modeling of the CH(3)-H(4)folate product into the enzyme active site suggests that Asp 120 may also play crucial roles in folate binding and catalysis. We have replaced Asp 120 with Asn, Ser, Ala, Val, and Lys and have characterized the mutant enzymes. Consistent with a loss of negative charge near the flavin, the midpoint potentials of the mutants increased from 17 to 30 mV. A small kinetic effect on the NADH reductive half-reaction was also observed as the mutants exhibited a 1.2-1.5-fold faster reduction rate than the wild-type enzyme. Catalytic efficiency (k(cat)/K(m)) in the CH(2)-H(4)folate oxidative half-reaction was decreased significantly (up to 70000-fold) and in a manner generally consistent with the negative charge density of position 120, supporting a major role for Asp 120 in electrostatic stabilization of the putative 5-iminium cation intermediate during catalysis. Asp 120 is also intimately involved in folate binding as increases in the apparent K(d) of up to 15-fold were obtained for the mutants. Examining the E(red) + CH(2)-H(4)folate reaction at 4 degrees C, we obtained, for the first time, evidence for the rapid formation of a reduced enzyme-folate complex with wild-type MTHFR. The more active Asp120Ala mutant, but not the severely impaired Asp120Lys mutant, demonstrated the species, suggesting a connection between the extent of complex formation and catalytic efficiency.
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Trimmer EE, Ballou DP, Ludwig ML, Matthews RG. Folate activation and catalysis in methylenetetrahydrofolate reductase from Escherichia coli: roles for aspartate 120 and glutamate 28. Biochemistry 2001; 40:6216-26. [PMID: 11371182 DOI: 10.1021/bi002790v] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The flavoprotein Escherichia coli methylenetetrahydrofolate reductase (MTHFR) catalyzes the reduction of 5,10-methylenetetrahydrofolate (CH(2)-H(4)folate) to 5-methyltetrahydrofolate (CH(3)-H(4)folate). The X-ray crystal structure of the enzyme has revealed the amino acids at the flavin active site that are likely to be relevant to catalysis. Here, we have focused on two conserved residues, Asp 120 and Glu 28. The presence of an acidic residue (Asp 120) near the N1-C2=O position of the flavin distinguishes MTHFR from all other known flavin oxidoreductases and suggests an important function for this residue in modulating the flavin reactivity. Modeling of the CH(3)-H(4)folate product into the enzyme active site also suggests roles for Asp 120 in binding of folate and in electrostatic stabilization of the putative 5-iminium cation intermediate during catalysis. In the NADH-menadione oxidoreductase assay and in the isolated reductive half-reaction, the Asp120Asn mutant enzyme is reduced by NADH 30% more rapidly than the wild-type enzyme, which is consistent with a measured increase in the flavin midpoint potential. Compared to the wild-type enzyme, the mutant showed 150-fold decreased activity in the physiological NADH-CH(2)-H(4)folate oxidoreductase reaction and in the oxidative half-reaction involving CH(2)-H(4)folate, but the apparent K(d) for CH(2)-H(4)folate was relatively unchanged. Our results support a role for Asp 120 in catalysis of folate reduction and perhaps in stabilization of the 5-iminium cation. By analogy to thymidylate synthase, which also uses CH(2)-H(4)folate as a substrate, Glu 28 may serve directly or via water as a general acid catalyst to aid in 5-iminium cation formation. Consistent with this role, the Glu28Gln mutant was unable to catalyze the reduction of CH(2)-H(4)folate and was inactive in the physiological oxidoreductase reaction. The mutant enzyme was able to bind CH(3)-H(4)folate, but reduction of the FAD cofactor was not observed. In the NADH-menadione oxidoreductase assay, the mutant demonstrated a 240-fold decrease in activity.
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Affiliation(s)
- E E Trimmer
- Department of Biological Chemistry and Biophysics Research Division, The University of Michigan, Ann Arbor, Michigan 48109-1055, USA
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Trimmer EE, Ballou DP, Matthews RG. Methylenetetrahydrofolate reductase from Escherichia coli: elucidation of the kinetic mechanism by steady-state and rapid-reaction studies. Biochemistry 2001; 40:6205-15. [PMID: 11371181 DOI: 10.1021/bi002789w] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The flavoprotein methylenetetrahydrofolate reductase (MTHFR) from Escherichia coli catalyzes the reduction of 5,10-methylenetetrahydrofolate (CH(2)-H(4)folate) to 5-methyltetrahydrofolate (CH(3)-H(4)folate) using NADH as the source of reducing equivalents. The enzyme also catalyzes the transfer of reducing equivalents from NADH or CH(3)-H(4)folate to menadione, an artificial electron acceptor. Here, we have determined the midpoint potential of the enzyme-bound flavin to be -237 mV. We have examined the individual reductive and oxidative half-reactions constituting the enzyme's activities. In an anaerobic stopped-flow spectrophotometer, we have measured the rate constants of flavin reduction and oxidation occurring in each half-reaction and have compared these with the observed catalytic turnover numbers measured under steady-state conditions. We have shown that, in all cases, the half-reactions proceed at rates sufficiently fast to account for overall turnover, establishing that the enzyme is kinetically competent to catalyze these oxidoreductions by a ping-pong Bi-Bi mechanism. Reoxidation of the reduced flavin by CH(2)-H(4)folate is substantially rate limiting in the physiological NADH-CH(2)-H(4)folate oxidoreductase reaction. In the NADH-menadione oxidoreductase reaction, the reduction of the flavin by NADH is rate limiting as is the reduction of flavin by CH(3)-H(4)folate in the CH(3)-H(4)folate-menadione oxidoreductase reaction. We conclude that studies of individual half-reactions catalyzed by E. coli MTHFR may be used to probe mechanistic questions relevant to the overall oxidoreductase reactions.
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Affiliation(s)
- E E Trimmer
- Department of Biological Chemistry and Biophysics Research Division, The University of Michigan, Ann Arbor, Michigan 48109-1055, USA
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Abstract
Cisplatin is a widely used anti-cancer drug that is exceptionally effective against testicular cancer. trans-DDP, the geometric isomer of cisplatin, is ineffective as a chemotherapeutic agent. The anti-tumour activity of cisplatin is generally attributed to its formation of DNA adducts, both intrastrand and interstrand crosslinks, which induce structural distortions in DNA. The DNA adducts of cisplatin are thought to mediate its cytotoxic effects by inhibiting DNA replication and transcription and, ultimately, by inducing programmed cell death, or apoptosis. The adducts of both cis- and trans-DDP are removed from DNA by the nucleotide-excision-repair pathway. Cellular proteins possessing certain DNA-binding motifs, including the HMG domain, bind selectively to DNA modified by cisplatin, but not to DNA adducts of trans-DDP; evidence suggests a possible role for these proteins in modulating cisplatin cytotoxicity. Both intrinsic and drug-induced resistance often limit the success of cisplatin; several specific mechanisms of cisplatin resistance have been identified.
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Affiliation(s)
- E E Trimmer
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge 02139, USA
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Sheppard CA, Trimmer EE, Matthews RG. Purification and properties of NADH-dependent 5, 10-methylenetetrahydrofolate reductase (MetF) from Escherichia coli. J Bacteriol 1999; 181:718-25. [PMID: 9922232 PMCID: PMC93435 DOI: 10.1128/jb.181.3.718-725.1999] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/1998] [Accepted: 11/09/1998] [Indexed: 11/20/2022] Open
Abstract
A K-12 strain of Escherichia coli that overproduces methylenetetrahydrofolate reductase (MetF) has been constructed, and the enzyme has been purified to apparent homogeneity. A plasmid specifying MetF with six histidine residues added to the C terminus has been used to purify histidine-tagged MetF to homogeneity in a single step by affinity chromatography on nickel-agarose, yielding a preparation with specific activity comparable to that of the unmodified enzyme. The native protein comprises four identical 33-kDa subunits, each of which contains a molecule of noncovalently bound flavin adenine dinucleotide (FAD). No additional cofactors or metals have been detected. The purified enzyme catalyzes the reduction of methylenetetrahydrofolate to methyltetrahydrofolate, using NADH as the reductant. Kinetic parameters have been determined at 15 degreesC and pH 7.2 in a stopped-flow spectrophotometer; the Km for NADH is 13 microM, the Km for CH2-H4folate is 0.8 microM, and the turnover number under Vmax conditions estimated for the reaction is 1,800 mol of NADH oxidized min-1 (mol of enzyme-bound FAD)-1. NADPH also serves as a reductant, but exhibits a much higher Km. MetF also catalyzes the oxidation of methyltetrahydrofolate to methylenetetrahydrofolate in the presence of menadione, which serves as an electron acceptor. The properties of MetF from E. coli differ from those of the ferredoxin-dependent methylenetetrahydrofolate reductase isolated from the homoacetogen Clostridium formicoaceticum and more closely resemble those of the NADH-dependent enzyme from Peptostreptococcus productus and the NADPH-dependent enzymes from eukaryotes.
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Affiliation(s)
- C A Sheppard
- Biophysics Research Division and Department of Biological Chemistry, The University of Michigan, Ann Arbor, Michigan 48109-1055, USA
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Trimmer EE, Zamble DB, Lippard SJ, Essigmann JM. Human testis-determining factor SRY binds to the major DNA adduct of cisplatin and a putative target sequence with comparable affinities. Biochemistry 1998; 37:352-62. [PMID: 9425057 DOI: 10.1021/bi971675q] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
cis-Diamminedichloroplatinum(II) (cis-DDP or cisplatin) is a widely used anticancer drug that is most effective against tumors of the testis. Although cisplatin is believed to mediate its cytotoxicity through the formation of DNA adducts, the precise biochemical mechanisms underlying its antitumor activity and selectivity for testicular tumors remain elusive. Of significance are the high-mobility group (HMG) domain and other proteins that bind specifically to cisplatin-DNA adducts. The present study focuses on the testis-specific HMG domain protein human SRY (hSRY). The full-length hSRY protein and its HMG domain region alone were expressed in Escherichia coli and purified to homogeneity. The affinities and specificities of full-length hSRY and the hSRY-HMG domain for 20 bp DNAs containing a single cis-[Pt(NH3)2{d(GpG)-N7(1), -N7(2)}] intrastrand cross-link or a putative hSRY target site in the CD3epsilon gene enhancer (AACAAAG) were determined in electrophoretic mobility shift assays. Full-length hSRY bound to the major 1,2-d(GpG) cisplatin adduct with a Kd(app) of 120 +/- 10 nM and exhibited a 20-fold specificity over unmodified DNA. The HMG domain of hSRY was sufficient for this interaction. The hSRY-HMG domain recognized the 1,2-d(GpG) intrastrand cross-link with higher affinity [Kd(app) = 4 +/- 0.7 nM] but with lower specificity (5-fold) than the full-length protein. The affinities of full-length hSRY and the hSRY-HMG domain for a single cisplatin-DNA adduct were comparable to those for the putative target sequence AACAAAG. These data suggest that cisplatin-DNA adducts may compete with specific DNA sequences in vivo for the binding of human SRY. A possible role for this testis-specific protein in the cytotoxicity and organotropic specificity of cisplatin for testicular tumors is proposed.
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Affiliation(s)
- E E Trimmer
- Department of Chemistry and Division of Toxicology, Whitaker College of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge 02139, USA
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