1
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Li H, Zhu D, Yang Y, Ma Y, Chen Y, Xue P, Chen J, Qin M, Xu D, Cai C, Cheng H. Determinants of DNMT2/TRDMT1 preference for substrates tRNA and DNA during the evolution. RNA Biol 2023; 20:875-892. [PMID: 37966982 PMCID: PMC10653749 DOI: 10.1080/15476286.2023.2272473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/12/2023] [Indexed: 11/17/2023] Open
Abstract
RNA methyltransferase DNMT2/TRDMT1 is the most conserved member of the DNMT family from bacteria to plants and mammals. In previous studies, we found some determinants for tRNA recognition of DNMT2/TRDMT1, but the preference mechanism of this enzyme for substrates tRNA and DNA remains to be explored. In the present study, CFT-containing target recognition domain (TRD) and target recognition extension domain (TRED) in DNMT2/TRDMT1 play a crucial role in the substrate DNA and RNA selection during the evolution. Moreover, the classical substrate tRNA for DNMT2/TRDMT1 had a characteristic sequence CUXXCAC in the anticodon loop. Position 35 was occupied by U, making cytosine-38 (C38) twist into the loop, whereas C, G or A was located at position 35, keeping the C38-flipping state. Hence, the substrate preference could be modulated by the easily flipped state of target cytosine in tRNA, as well as TRD and TRED. Additionally, DNMT2/TRDMT1 cancer mutant activity was collectively mediated by five enzymatic characteristics, which might impact gene expressions. Importantly, G155C, G155V and G155S mutations reduced enzymatic activities and showed significant associations with diseases using seven prediction methods. Altogether, these findings will assist in illustrating the substrate preference mechanism of DNMT2/TRDMT1 and provide a promising therapeutic strategy for cancer.
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Affiliation(s)
- Huari Li
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Daiyun Zhu
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Yapeng Yang
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Yunfei Ma
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Yong Chen
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Pingfang Xue
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Juan Chen
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Mian Qin
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Dandan Xu
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Chao Cai
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Hongjing Cheng
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, China
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2
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Ye F, Kong X, Zhang H, Liu Y, Shao Z, Jin J, Cai Y, Zhang R, Li L, Zhang YW, Liu YC, Zhang C, Xie W, Yu K, Ding H, Zhao K, Chen S, Jiang H, Baylin SB, Luo C. Biochemical Studies and Molecular Dynamic Simulations Reveal the Molecular Basis of Conformational Changes in DNA Methyltransferase-1. ACS Chem Biol 2018; 13:772-781. [PMID: 29381856 DOI: 10.1021/acschembio.7b00890] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
DNA methyltransferase-1 (DNMT1) plays a crucial role in the maintenance of genomic methylation patterns. The crystal structure of DNMT1 was determined in two different states in which the helix that follows the catalytic loop was either kinked (designated helix-kinked) or well folded (designated helix-straight state). Here, we show that the proper structural transition between these two states is required for DNMT1 activity. The mutations of N1248A and R1279D, which did not affect interactions between DNMT1 and substrates or cofactors, allosterically reduced enzymatic activities in vitro by decreasing kcat/ Km for AdoMet. The crystallographic data combined with molecular dynamic (MD) simulations indicated that the N1248A and R1279D mutants bias the catalytic helix to either the kinked or straight conformation. In addition, genetic complementation assays for the two mutants suggested that disturbing the conformational transition reduced DNMT1 activity in cells, which could act additively with existing DNMT inhibitors to decrease DNA methylation. Collectively, our studies provide molecular insights into conformational changes of the catalytic helix, which is essential for DNMT1 catalytic activity, and thus aid in better understanding the relationship between DNMT1 dynamic switching and enzymatic activity.
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Affiliation(s)
- Fei Ye
- College of Life Sciences, Zhejiang Sci-Tech University, Hangzhou 310018, China
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Xiangqian Kong
- Department of Oncology, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, United States
| | - Hao Zhang
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Yan Liu
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Zhiyuan Shao
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Jia Jin
- College of Life Sciences, Zhejiang Sci-Tech University, Hangzhou 310018, China
| | - Yi Cai
- Department of Oncology, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, United States
| | - Rukang Zhang
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Linjuan Li
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Yang W. Zhang
- Department of Oncology, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, United States
| | - Yu-Chih Liu
- Shanghai ChemPartner Co., LTD, Building 5, 998 Halei Road, Zhangjiang Hi-Tech Park,
Pudong New Area, Shanghai 201203, P.R. China
| | - Chenhua Zhang
- Shanghai ChemPartner Co., LTD, Building 5, 998 Halei Road, Zhangjiang Hi-Tech Park,
Pudong New Area, Shanghai 201203, P.R. China
| | - Wenbing Xie
- Department of Oncology, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, United States
| | - Kunqian Yu
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Hong Ding
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
- School of Pharmacy, Shanghai University of Traditional Chinese Medicine, 1200 Cailun Road, Shanghai 201203, China
| | - Kehao Zhao
- China Novartis Institutes for BioMedical Research, Shanghai 201203, China
| | - Shijie Chen
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Hualiang Jiang
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Stephen B. Baylin
- Department of Oncology, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, United States
| | - Cheng Luo
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
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3
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Metadynamics simulation study on the conformational transformation of HhaI methyltransferase: an induced-fit base-flipping hypothesis. BIOMED RESEARCH INTERNATIONAL 2014; 2014:304563. [PMID: 25045662 PMCID: PMC4090504 DOI: 10.1155/2014/304563] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Accepted: 05/12/2014] [Indexed: 12/02/2022]
Abstract
DNA methyltransferases play crucial roles in establishing and maintenance of DNA methylation, which is an important epigenetic mark. Flipping the target cytosine out of the DNA helical stack and into the active site of protein provides DNA methyltransferases with an opportunity to access and modify the genetic information hidden in DNA. To investigate the conversion process of base flipping in the HhaI methyltransferase (M.HhaI), we performed different molecular simulation approaches on M.HhaI-DNA-S-adenosylhomocysteine ternary complex. The results demonstrate that the nonspecific binding of DNA to M.HhaI is initially induced by electrostatic interactions. Differences in chemical environment between the major and minor grooves determine the orientation of DNA. Gln237 at the target recognition loop recognizes the GCGC base pair from the major groove side by hydrogen bonds. In addition, catalytic loop motion is a key factor during this process. Our study indicates that base flipping is likely to be an “induced-fit” process. This study provides a solid foundation for future studies on the discovery and development of mechanism-based DNA methyltransferases regulators.
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4
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Matje DM, Krivacic CT, Dahlquist FW, Reich NO. Distal structural elements coordinate a conserved base flipping network. Biochemistry 2013; 52:1669-76. [PMID: 23409802 DOI: 10.1021/bi301284f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
One of the most dramatic illustrations of enzymatic promotion of a high-energy intermediate is observed in DNA modification and repair enzymes where an individual base is rotated (flipped) 180° around the deoxyribose-phosphate backbone and into the active site. While the end states have been extensively characterized, experimental techniques have yet to yield a full description of the base flipping process and the role played by the enzyme. The C5 cytosine methyltransferase M.HhaI coordinates an ensemble of reciprocal DNA and enzyme rearrangements to efficiently flip the target cytosine from the DNA helix. We sought to understand the role of individual amino acids during base flipping. Our results demonstrate that M.HhaI initiates base flipping before closure of the catalytic loop and utilizes the conserved serine 85 in the catalytic loop to accelerate flipping and maintain distortion of the DNA backbone. Serine 87, which forms specific contacts within the DNA helix after base flipping, is not involved in the flipping process or in maintaining the catalytically competent complex. At the base of the catalytic loop, glycine 98 acts as a hinge to allow conformational dynamism of the loop and mutation to alanine inhibits stabilization of the closed loop. Our results illustrate how an enzyme utilizes numerous, distal residues in concert to transform substrate recognition into catalysis.
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Affiliation(s)
- Douglas M Matje
- Department of Chemistry and Biochemistry, University of California , Santa Barbara, California 93106-9510, United States
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5
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Zhou H, Purdy MM, Dahlquist FW, Reich NO. The Recognition Pathway for the DNA Cytosine Methyltransferase M.HhaI,. Biochemistry 2009; 48:7807-16. [DOI: 10.1021/bi900502g] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Hongjun Zhou
- Department of Chemistry and Biochemistry, University of California at Santa Barbara, Santa Barbara, California 93106-9510
| | - Matthew M. Purdy
- Department of Chemistry and Biochemistry, University of California at Santa Barbara, Santa Barbara, California 93106-9510
| | - Frederick W. Dahlquist
- Department of Chemistry and Biochemistry, University of California at Santa Barbara, Santa Barbara, California 93106-9510
| | - Norbert O. Reich
- Department of Chemistry and Biochemistry, University of California at Santa Barbara, Santa Barbara, California 93106-9510
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6
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Estabrook RA, Nguyen TT, Fera N, Reich NO. Coupling sequence-specific recognition to DNA modification. J Biol Chem 2009; 284:22690-6. [PMID: 19497854 DOI: 10.1074/jbc.m109.015966] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Enzymes that modify DNA are faced with significant challenges in specificity for both substrate binding and catalysis. We describe how single hydrogen bonds between M.HhaI, a DNA cytosine methyltransferase, and its DNA substrate regulate the positioning of a peptide loop which is approximately 28 A away. Stopped-flow fluorescence measurements of a tryptophan inserted into the loop provide real-time observations of conformational rearrangements. These long-range interactions that correlate with substrate binding and critically, enzyme turnover, will have broad application to enzyme specificity and drug design for this medically relevant class of enzymes.
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Affiliation(s)
- R August Estabrook
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA
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7
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Shieh FK, Reich NO. AdoMet-dependent Methyl-transfer: Glu119 Is Essential for DNA C5-Cytosine Methyltransferase M.HhaI. J Mol Biol 2007; 373:1157-68. [PMID: 17897676 DOI: 10.1016/j.jmb.2007.08.009] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2007] [Revised: 07/17/2007] [Accepted: 08/03/2007] [Indexed: 11/21/2022]
Abstract
The role of Glu119 in S-adenosyl-L-methionine-dependent DNA methyltransferase M.HhaI-catalyzed DNA methylation was studied. Glu119 belongs to the highly conserved Glu/Asn/Val motif found in all DNA C5-cytosine methyltransferases, and its importance for M.HhaI function remains untested. We show that formation of the covalent intermediate between Cys81 and the target cytosine requires Glu119, since conversion to Ala, Asp or Gln lowers the rate of methyl transfer 10(2)-10(6) fold. Further, unlike the wild-type M.HhaI, these mutants are not trapped by the substrate in which the target cytosine is replaced with the mechanism-based inhibitor 5-fluorocytosine. The DNA binding affinity for the Glu119Asp mutant is decreased 10(3)-fold. Thus, the ability of the enzyme to stabilize the extrahelical cytosine is coupled directly to tight DNA binding. The structures of the ternary protein/DNA/AdoHcy complexes for both the Glu119Ala and Glu119Gln mutants (2.70 A and 2.75 A, respectively) show that the flipped base is positioned nearly identically with that observed in the wild-type M.HhaI complex. A single water molecule in the Glu119Ala structure between Ala119 and the extrahelical cytosine N3 is lacking in the Glu119Gln and wild-type M.HhaI structures, and most likely accounts for this mutant's partial activity. Glu119 has essential roles in activating the target cytosine for nucleophilic attack and contributes to tight DNA binding.
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Affiliation(s)
- Fa-Kuen Shieh
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106-9510, USA
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8
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Youngblood B, Shieh FK, Buller F, Bullock T, Reich NO. S-adenosyl-L-methionine-dependent methyl transfer: observable precatalytic intermediates during DNA cytosine methylation. Biochemistry 2007; 46:8766-75. [PMID: 17616174 DOI: 10.1021/bi7005948] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
S-adenosyl-L-methionine- (AdoMet-) dependent methyltransferases are widespread, play critical roles in diverse biological pathways, and are antibiotic and cancer drug targets. Presently missing from our understanding of any AdoMet-dependent methyl-transfer reaction is a high-resolution structure of a precatalytic enzyme/AdoMet/DNA complex. The catalytic mechanism of DNA cytosine methylation was studied by structurally and functionally characterizing several active site mutants of the bacterial enzyme M.HhaI. The 2.64 A resolution protein/DNA/AdoMet structure of the inactive C81A M.HhaI mutant suggests that active site water, an approximately 13 degree tilt of the target base toward the active site nucleophile, and the presence or absence of the cofactor methylsulfonium are coupled via a hydrogen-bonding network involving Tyr167. The active site in the mutant complex is assembled to optimally align the pyrimidine for nucleophilic attack and subsequent methyl transfer, consistent with previous molecular dynamics ab initio and quantum mechanics/molecular mechanics calculations. The mutant/DNA/AdoHcy structure (2.88 A resolution) provides a direct comparison to the postcatalytic complex. A third C81A ternary structure (2.22 A resolution) reveals hydrolysis of AdoMet to adenosine in the active site, further validating the coupling between the methionine portion of AdoMet and ultimately validating the structural observation of a prechemistry/postchemistry water network. Disruption of this hydrogen-bonding network by a Tyr167 to Phe167 mutation does not alter the kinetics of nucleophilic attack or methyl transfer. However, the Y167F mutant shows detectable changes in kcat, caused by the perturbed kinetics of AdoHcy release. These results provide a basis for including an extensive hydrogen-bonding network in controlling the rate-limiting product release steps during cytosine methylation.
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Affiliation(s)
- Ben Youngblood
- Program in Biomolecular Science and Engineering, University of California, Santa Barbara, California 93106-9510, USA
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9
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Zhou H, Shatz W, Purdy MM, Fera N, Dahlquist FW, Reich NO. Long-range structural and dynamical changes induced by cofactor binding in DNA methyltransferase M.HhaI. Biochemistry 2007; 46:7261-8. [PMID: 17523600 DOI: 10.1021/bi602662e] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The bacterial DNA cytosine methyltransferase M.HhaI sequence-specifically modifies DNA in an S-adenosylmethionine dependent reaction. The enzyme stabilizes the target cytosine (GCGC) into an extrahelical position, with a concomitant large movement of an active site loop involving residues 80-99. We used multidimensional, transverse relaxation-optimized NMR experiments to assign nearly 80% of all residues in the cofactor-bound enzyme form, providing a basis for detailed structural and dynamical characterization. We examined details of the previously unknown effects of the cofactor binding with M.HhaI in solution. Addition of the cofactor results in numerous structural changes throughout the protein, including those decorating the cofactor binding site, and distal residues more than 30 A away. The active site loop is involved in motions both on a picosecond to nanosecond time scale and on a microsecond to millisecond time scale and is not significantly affected by cofactor binding except for a few N-terminal residues. The cofactor also affects residues near the DNA binding cleft, suggesting a role for the cofactor in regulating DNA interactions. The allosteric properties we observed appear to be closely related to the significant amount of dynamics and dynamical changes in response to ligand binding detected in the protein.
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Affiliation(s)
- Hongjun Zhou
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106-9510, USA
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10
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Estabrook RA, Reich N. Observing an Induced-fit Mechanism during Sequence-specific DNA Methylation. J Biol Chem 2006; 281:37205-14. [PMID: 17005571 DOI: 10.1074/jbc.m607538200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The characterization of conformational changes that drive induced-fit mechanisms and their quantitative importance to enzyme specificity are essential for a full understanding of enzyme function. Here, we report on M.HhaI, a sequence-specific DNA cytosine C(5) methyltransferase that reorganizes a flexible loop (residues 80-100) upon binding cognate DNA as part of an induced-fit mechanism. To directly observe this approximately 26A conformational rearrangement and provide a basis for understanding its importance to specificity, we replaced loop residues Lys-91 and Glu-94 with tryptophans. The double mutants W41F/K91W and W41F/E94W are relatively unperturbed in kinetic and thermodynamic properties. W41F/E94W shows DNA sequence-dependent changes in fluorescence: significant changes in equilibrium and transient state fluorescence that occur when the enzyme binds cognate DNA are absent with nonspecific DNA. These real-time, solution-based results provide direct evidence that binding to cognate DNA induces loop reorganization into the closed conformer, resulting in the correct assembly of the active site. We propose that M.HhaI scans nonspecific DNA in the loop-open conformer and rearranges to the closed form once the cognate site is recognized. The fluorescence data exclude mechanisms in which loop motion precedes base flipping, and we show loop rearrangements are directly coupled to base flipping, because the sequential removal of single hydrogen bonds within the target guanosine:cytosine base pair results in corresponding changes in loop motion.
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Affiliation(s)
- R August Estabrook
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA
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11
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Shieh FK, Youngblood B, Reich NO. The role of Arg165 towards base flipping, base stabilization and catalysis in M.HhaI. J Mol Biol 2006; 362:516-27. [PMID: 16926025 DOI: 10.1016/j.jmb.2006.07.030] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2006] [Revised: 07/13/2006] [Accepted: 07/14/2006] [Indexed: 10/24/2022]
Abstract
Arg165 forms part of a previously identified base flipping motif in the bacterial DNA cytosine methyltransferase, M.HhaI. Replacement of Arg165 with Ala has no detectable effect on either DNA or AdoMet affinity, yet causes the base flipping and restacking transitions to be decreased approximately 16 and 190-fold respectively, thus confirming the importance of this motif. However, these kinetic changes cannot account for the mutant's observed 10(5)-fold decreased catalytic rate. The mutant enzyme/cognate DNA cocrystal structure (2.79 A resolution) shows the target cytosine to be positioned approximately 30 degrees into the major groove, which is consistent with a major groove pathway for nucleotide flipping. The pyrimidine-sugar chi angle is rotated to approximately +171 degrees, from a range of -95 degrees to -120 degrees in B DNA, and -77 degrees in the WT M.HhaI complex. Thus, Arg165 is important for maintaining the cytosine positioned for nucleophilic attack by Cys81. The cytosine sugar pucker is in the C2'-endo-C3'-exo (South conformation), in contrast to the previously reported C3'-endo (North conformation) described for the original 2.70 A resolution cocrystal structure of the WT M.HhaI/DNA complex. We determined a high resolution structure of the WT M.HhaI/DNA complex (1.96 A) to better determine the sugar pucker. This new structure is similar to the original, lower resolution WT M.HhaI complex, but shows that the sugar pucker is O4'-endo (East conformation), intermediate between the South and North conformers. In summary, Arg165 plays significant roles in base flipping, cytosine positioning, and catalysis. Furthermore, the previously proposed M.HhaI-mediated changes in sugar pucker may not be an important contributor to the base flipping mechanism. These results provide insights into the base flipping and catalytic mechanisms for bacterial and eukaryotic DNA methyltransferases.
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Affiliation(s)
- Fa-Kuen Shieh
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106-9510, USA
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