301
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Huang N, MacKerell AD. Atomistic view of base flipping in DNA. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2004; 362:1439-1460. [PMID: 15306460 DOI: 10.1098/rsta.2004.1383] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Base flipping is essential for the enzyme-catalysed methylation of DNA. In our previous studies, the flipping of bases out of duplex DNA in DNA alone and when bound to the (cytosine-C5)-methyltransferase from HhaI (M.HhaI) were investigated via potential of mean force calculations. Insights into various experimental observations were obtained. In the present paper we present an overview of previous computational studies of base flipping along with new detailed structural and energetic analysis on atomic events that contribute to the free energy surfaces. The contributions from different intrinsic and environmental effects to the base-flipping process are explored, and experimental data derived from a variety of methods are reconciled. A detailed protein-facilitated base-flipping mechanism is proposed. Ground-state destabilization is achieved via disruption of the target base Watson-Crick interactions by substitution with favourable DNA-protein interactions. In addition, specific DNA-protein interactions and favourable solvation effects further promote target base flipping along the major groove through the protein matrix, and maximal interactions occur between the DNA and the protein upon reaching the fully flipped state. Other DNA binding proteins that involve distortion of DNA's conformation may use a similar mechanism to that by which M.HhaI facilitates base flipping.
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Affiliation(s)
- Niu Huang
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, 20 Penn Street, Baltimore, MD 21201, USA
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302
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Tanaka Y, Tsumoto K, Yasutake Y, Umetsu M, Yao M, Fukada H, Tanaka I, Kumagai I. How Oligomerization Contributes to the Thermostability of an Archaeon Protein. J Biol Chem 2004; 279:32957-67. [PMID: 15169774 DOI: 10.1074/jbc.m404405200] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To study how oligomerization may contribute to the thermostability of archaeon proteins, we focused on a hexameric protein, protein L-isoaspartyl-O-methyltransferase from Sulfolobus tokodaii (StoPIMT). The crystal structure shows that StoPIMT has a distinctive hexameric structure composed of monomers consisting of two domains: an S-adenosylmethionine-dependent methyltransferase fold domain and a C-terminal alpha-helical domain. The hexameric structure includes three interfacial contact regions: major, minor, and coiled-coil. Several C-terminal deletion mutants were constructed and characterized. The hexameric structure and thermostability were retained when the C-terminal alpha-helical domain (Tyr(206)-Thr(231)) was deleted, suggesting that oligomerization via coiled-coil association using the C-terminal alpha-helical domains did not contribute critically to hexamerization or to the increased thermostability of the protein. Deletion of three additional residues located in the major contact region, Tyr(203)-Asp(204)-Asp(205), led to a significant decrease in hexamer stability and chemico/thermostability. Although replacement of Thr(146) and Asp(204), which form two hydrogen bonds in the interface in the major contact region, with Ala did not affect hexamer formation, these mutations led to a significant decrease in thermostability, suggesting that two residues in the major contact region make significant contributions to the increase in stability of the protein via hexamerization. These results suggest that cooperative hexamerization occurs via interactions of "hot spot" residues and that a couple of interfacial hot spot residues are responsible for enhancing thermostability via oligomerization.
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Affiliation(s)
- Yoshikazu Tanaka
- Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aoba-yama 07, Aoba-ku, Sendai 980-8579, Japan
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303
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Maravić G, Bujnicki JM, Flögel M. Mutational analysis of basic residues in the N-terminus of the rRNA:m6A methyltransferase ErmC'. Folia Microbiol (Praha) 2004; 49:3-7. [PMID: 15114858 DOI: 10.1007/bf02931637] [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] [Indexed: 10/21/2022]
Abstract
Erm methyltransferases mediate the resistance to the macrolide-lincosamide-streptogramin B antibiotics via dimethylation of a specific adenine residue in 23S rRNA. The role of positively charged N-terminal residues of the ErmC' methyltransferase in RNA binding and/or catalysis was determined. Mutational analysis of amino acids K4 and K7 was performed and the mutants were characterized in in vivo and in vitro experiments. The K4 and K7 residues were suggested not to be essential for the enzyme activity but to provide a considerable support for the catalytic step of the reaction, probably by maintaining the optimum conformation of the transition state through interactions with the phosphate backbone of RNA.
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Affiliation(s)
- G Maravić
- Department of Biochemistry and Molecular Biology, Faculty of Pharmacy and Biochemistry, Univesity of Zagreb, 10000 Zagreb, Croatia.
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304
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Smith CV, Sharma V, Sacchettini JC. TB drug discovery: addressing issues of persistence and resistance. Tuberculosis (Edinb) 2004; 84:45-55. [PMID: 14670345 DOI: 10.1016/j.tube.2003.08.019] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Tuberculosis remains a leading cause of mortality worldwide into the 21st century. Among the main obstacles to the global control of the disease are emerging multi-drug resistant strains and the recalcitrance of persistent infections to treatment with conventional anti-TB drugs. Here we review recent developments in our understanding of some of the pathways involved in a persistent infection and pathogenesis of Mycobacterium tuberculosis, which reveal new targets for drug development. We describe the high-resolution crystal structures of enzymes of the glyoxylate shunt, isocitrate lyase and malate synthase, and of the cyclopropane synthases of mycolic acid biosynthesis. Structure-based drug design is now underway with the potential to lead to the development of new anti-tuberculars effective against persistent and resistant Mycobacterium tuberculosis infections.
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Affiliation(s)
- Clare V Smith
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128, USA
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305
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Larivière L, Moréra S. Structural evidence of a passive base-flipping mechanism for beta-glucosyltransferase. J Biol Chem 2004; 279:34715-20. [PMID: 15178685 DOI: 10.1074/jbc.m404394200] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Beta-glucosyltransferase (BGT) is a DNA-modifying enzyme and a glycosyltransferase. This inverting enzyme transfers glucose from UDP-glucose to the 5-hydroxymethyl cytosine bases of T4 phage DNA. From previous structural analyses we showed that Asp-100 and Asn-70 were, respectively, the catalytic base and the key residue for specific DNA recognition (Larivière, L., Gueguen-Chaignon, V., and Moréra, S. (2003) J. Mol. Biol. 330, 1077-1086). Here, we supply biochemical evidence supporting their essential roles in catalysis. We have also shown previously that BGT uses a base-flipping mechanism to access 5-hydroxymethyl cytosine (Larivière, L., and Moréra, S. (2002) J. Mol. Biol. 324, 483-490). Whether it is an active or a passive process remains unclear, as is the case for all DNA cleaving and modifying enzymes. Here, we report two crystal structures: (i) BGT in complex with a 13-mer DNA containing an A:G mismatch and (ii) BGT in a ternary complex with UDP and an oligonucleotide containing a single central G:C base pair. The binary structure reveals a specific complex with the flipped-out, mismatched adenine exposed to the active site. Unexpectedly, the other structure shows the non-productive binding of an intermediate flipped-out base. Our structural analysis provides clear evidence for a passive process.
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Affiliation(s)
- Laurent Larivière
- Laboratoire d'Enzymologie et Biochimie Structurales, Unité Propre de Recherche 9063 CNRS, Bātiment 34, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette, France
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306
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Subach OM, Khoroshaev AV, Gerasimov DN, Baskunov VB, Shchyolkina AK, Gromova ES. 2-Pyrimidinone as a probe for studying the EcoRII DNA methyltransferase-substrate interaction. ACTA ACUST UNITED AC 2004; 271:2391-9. [PMID: 15182354 DOI: 10.1111/j.1432-1033.2004.04158.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
EcoRII DNA methyltransferase (M.EcoRII) recognizes the 5' em leader CC*T/AGG em leader 3' DNA sequence and catalyzes the transfer of the methyl group from S-adenosyl-l-methionine to the C5 position of the inner cytosine residue (C*). Here, we study the mechanism of inhibition of M.EcoRII by DNA containing 2-pyrimidinone, a cytosine analogue lacking an NH(2) group at the C4 position of the pyrimidine ring. Also, DNA containing 2-pyrimidinone was used for probing contacts of M.EcoRII with functional groups of pyrimidine bases of the recognition sequence. 2-Pyrimidinone was incorporated into the 5' em leader CCT/AGG em leader 3' sequence replacing the target and nontarget cytosine and central thymine residues. Study of the DNA stability using thermal denaturation of 2-pyrimidinone containing duplexes pointed to the influence of the bases adjacent to 2-pyrimidinone and to a greater destabilizing influence of 2-pyrimidinone substitution for thymine than that for cytosine. Binding of M.EcoRII to 2-pyrimidinone containing DNA and methylation of these DNA demonstrate that the amino group of the outer cytosine in the EcoRII recognition sequence is not involved in the DNA-M.EcoRII interaction. It is probable that there are contacts between the functional groups of the central thymine exposed in the major groove and M.EcoRII. 2-Pyrimidinone replacing the target cytosine in the EcoRII recognition sequence forms covalent adducts with M.EcoRII. In the absence of the cofactor S-adenosyl-l-methionine, proton transfer to the C5 position of 2-pyrimidinone occurs and in the presence of S-adenosyl-l-methionine, methyl transfer to the C5 position of 2-pyrimidinone occurs.
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307
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Albrecht M, Lengauer T. Novel Sm-like proteins with long C-terminal tails and associated methyltransferases. FEBS Lett 2004; 569:18-26. [PMID: 15225602 DOI: 10.1016/j.febslet.2004.03.126] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2003] [Revised: 03/11/2004] [Accepted: 03/15/2004] [Indexed: 11/17/2022]
Abstract
Sm and Sm-like proteins of the Lsm (like Sm) domain family are generally involved in essential RNA-processing tasks. While recent research has focused on the function and structure of small family members, little is known about Lsm domain proteins carrying additional domains. Using an integrative bioinformatics approach, we discovered five novel groups of Lsm domain proteins (Lsm12-16) with long C-terminal tails and investigated their functions. All of them are evolutionarily conserved in eukaryotes with an N-terminal Lsm domain to bind nucleic acids followed by as yet uncharacterized C-terminal domains and sequence motifs. Based on known yeast interaction partners, Lsm12-16 may play important roles in RNA metabolism. Particularly, Lsm12 is possibly involved in mRNA degradation or tRNA splicing, and Lsm13-16 in the regulation of the mitotic G2/M phase. Lsm16 proteins have an additional C-terminal YjeF_N domain of as yet unknown function. The identification of an additional methyltransferase domain at the C-terminus of one of the Lsm12 proteins also led to the recognition of three new groups of methyltransferases, presumably dependent on S-adenosyl-l-methionine. Further computational analyses revealed that some methyltransferases contain putative RNA-binding helix-turn-helix domains and zinc fingers.
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Affiliation(s)
- Mario Albrecht
- Max-Planck-Institute for Informatics, Stuhlsatzenhausweg 85, 66123 Saarbrücken, Germany.
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308
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David A, Bleimling N, Beuck C, Lehn JM, Weinhold E, Teulade-Fichou MP. DNA mismatch-specific base flipping by a bisacridine macrocycle. Chembiochem 2004; 4:1326-31. [PMID: 14661275 DOI: 10.1002/cbic.200300693] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Most, if not all, enzymes that chemically modify nucleobases in DNA flip their target base from the inside of the double helix into an extrahelical position. This energetically unfavorable conformation is partly stabilized by specific binding of the apparent abasic site being formed. Thus, DNA base-flipping enzymes, like DNA methyltransferases and DNA glycosylases, generally bind very strongly to DNA containing abasic sites or abasic-site analogues. The macrocyclic bisacridine BisA has previously been shown to bind abasic sites. Herein we demonstrate that it is able to specifically recognize DNA base mismatches and most likely induces base flipping. Specific binding of BisA to DNA mismatches was studied by thermal denaturation experiments by using short duplex oligodeoxynucleotides containing central TT, TC, or TG mismatches or a TA match. In the presence of the macrocycle a strong increase in the melting temperature of up to 7.1 degrees C was observed for the mismatch-containing duplexes, whereas the melting temperature of the fully matched duplex was unaffected. Furthermore, BisA binding induced an enhanced reactivity of the mispaired thymine residue in the DNA toward potassium permanganate oxidation. A comparable reactivity has previously been observed for a TT target base mismatch in the presence of DNA methyltransferase M.TaqI. This similarity to a known base-flipping enzyme suggests that insertion of BisA into the DNA helix displaces the mispaired thymine residue into an extrahelical position, where it should be more prone to chemical oxidation. Thus, DNA base flipping does not appear to be limited to DNA-modifying enzymes but it is likely to also be induced by a small synthetic molecule binding to a thermodynamically weakened site in DNA.
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Affiliation(s)
- Arnaud David
- Laboratoire de Chimie des Interactions Moléculaires, Collège de France, CNRS UPR 285, 11 place Marcelin Berthelot, 75005 Paris, France
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309
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Bujnicki JM, Feder M, Ayres CL, Redman KL. Sequence-structure-function studies of tRNA:m5C methyltransferase Trm4p and its relationship to DNA:m5C and RNA:m5U methyltransferases. Nucleic Acids Res 2004; 32:2453-63. [PMID: 15121902 PMCID: PMC419452 DOI: 10.1093/nar/gkh564] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Three types of methyltransferases (MTases) generate 5-methylpyrimidine in nucleic acids, forming m5U in RNA, m5C in RNA and m5C in DNA. The DNA:m5C MTases have been extensively studied by crystallographic, biophysical, biochemical and computational methods. On the other hand, the sequence-structure-function relationships of RNA:m5C MTases remain obscure, as do the potential evolutionary relationships between the three types of 5-methylpyrimidine-generating enzymes. Sequence analyses and homology modeling of the yeast tRNA:m5C MTase Trm4p (also called Ncl1p) provided a structural and evolutionary platform for identification of catalytic residues and modeling of the architecture of the RNA:m5C MTase active site. The analysis led to the identification of two invariant residues that are important for Trm4p activity in addition to the conserved Cys residues in motif IV and motif VI that were previously found to be critical. The newly identified residues include a Lys residue in motif I and an Asp in motif IV. A conserved Gln found in motif X was found to be dispensable for MTase activity. Locations of essential residues in the model of Trm4p are in very good agreement with the X-ray structure of an RNA:m5C MTase homolog PH1374. Theoretical and experimental analyses revealed that RNA:m5C MTases share a number of features with either RNA:m5U MTases or DNA:m5C MTases, which suggested a tentative phylogenetic model of relationships between these three classes of 5-methylpyrimidine MTases. We infer that RNA:m5C MTases evolved from RNA:m5U MTases by acquiring an additional Cys residue in motif IV, which was adapted to function as the nucleophilic catalyst only later in DNA:m5C MTases, accompanied by loss of the original Cys from motif VI, transfer of a conserved carboxylate from motif IV to motif VI and sequence permutation.
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Affiliation(s)
- Janusz M Bujnicki
- Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology, Warsaw, Poland
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310
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Ishikawa I, Sakai N, Tamura T, Yao M, Watanabe N, Tanaka I. Crystal structure of human p120 homologue protein PH1374 from Pyrococcus horikoshii. Proteins 2004; 54:814-6. [PMID: 14997580 DOI: 10.1002/prot.10645] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Idumi Ishikawa
- Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan
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311
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Su TJ, Connolly BA, Darlington C, Mallin R, Dryden DTF. Unusual 2-aminopurine fluorescence from a complex of DNA and the EcoKI methyltransferase. Nucleic Acids Res 2004; 32:2223-30. [PMID: 15107490 PMCID: PMC407817 DOI: 10.1093/nar/gkh531] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The methyltransferase, M.EcoKI, recognizes the DNA sequence 5'-AACNNNNNNGTGC-3' and methylates adenine at the underlined positions. DNA methylation has been shown by crystallography to occur via a base flipping mechanism and is believed to be a general mechanism for all methyltransferases. If no structure is available, the fluorescence of 2-aminopurine is often used as a signal for base flipping as it shows enhanced fluorescence when its environment is perturbed. We find that 2-aminopurine gives enhanced fluorescence emission not only when it is placed at the M.EcoKI methylation sites but also at a location adjacent to the target adenine. Thus it appears that 2-aminopurine fluorescence intensity is not a clear indicator of base flipping but is a more general measure of DNA distortion. Upon addition of the cofactor S-adenosyl-methionine to the M.EcoKI:DNA complex, the 2-aminopurine fluorescence changes to that of a new species showing excitation at 345 nm and emission at 450 nm. This change requires a fully active enzyme, the correct cofactor and the 2-aminopurine located at the methylation site. However, the new fluorescent species is not a covalently modified form of 2-aminopurine and we suggest that it represents a hitherto undetected physicochemical form of 2-aminopurine.
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Affiliation(s)
- T-J Su
- School of Chemistry, University of Edinburgh, The King's Buildings, Edinburgh EH9 3JJ, UK
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312
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Kossykh VG, Lloyd RS. A DNA adenine methyltransferase of Escherichia coli that is cell cycle regulated and essential for viability. J Bacteriol 2004; 186:2061-7. [PMID: 15028690 PMCID: PMC374390 DOI: 10.1128/jb.186.7.2061-2067.2004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
DNA sequence analysis revealed that the putative yhdJ DNA methyltransferase gene of Escherichia coli is 55% identical to the Nostoc sp. strain PCC7120 gene encoding DNA methyltransferase AvaIII, which methylates adenine in the recognition sequence, ATGCAT. The yhdJ gene was cloned, and the enzyme was overexpressed and purified. Methylation and restriction analysis showed that the DNA methyltransferase methylates the first adenine in the sequence ATGCAT. This DNA methylation was found to be regulated during the cell cycle, and the DNA adenine methyltransferase was designated M.EcoKCcrM (for "cell cycle-regulated methyltransferase"). The CcrM DNA adenine methyltransferase is required for viability in E. coli, as a strain lacking a functional genomic copy of ccrM can be isolated only in the presence of an additional copy of ccrM supplied in trans. The cells of such a knockout strain stopped growing when expression of the inducible plasmid ccrM gene was shut off. Overexpression of M.EcoKCcrM slowed bacterial growth, and the ATGCAT sites became fully methylated throughout the cell cycle; a high proportion of cells with an anomalous size distribution and DNA content was found in this population. Thus, the temporal control of this methyltransferase may contribute to accurate cell cycle control of cell division and cellular morphology. Homologs of M.EcoKCcrM are present in other bacteria belonging to the gamma subdivision of the class Proteobacteria, suggesting that methylation at ATGCAT sites may have similar functions in other members of this group.
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Affiliation(s)
- Valeri G Kossykh
- Sealy Center for Molecular Science and Department of Human Biological Chemistry and Genetics, University of Texas Medical Branch at Galveston, Galveston, Texas 77555-1071, USA.
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313
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Cotton NJH, Stoddard B, Parson WW. Oxidative inhibition of human soluble catechol-O-methyltransferase. J Biol Chem 2004; 279:23710-8. [PMID: 15031283 DOI: 10.1074/jbc.m401086200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
A common polymorphism in the human gene for catechol-O-methyltransferase results in replacement of Val-108 by Met in the soluble form of the protein (s-COMT) and has been linked to breast cancer and neuropsychiatric disorders. The 108M and 108V variants are reported to differ in their thermal stability, with 108M COMT losing catalytic activity more rapidly. Because human s-COMT contains seven cysteine residues and includes CXXC and CXXS motifs that are associated with thiol-disulfide redox reactions, we examined the effects of reducing and oxidizing conditions on the enzyme. In the absence of a reductant 108M s-COMT lost activity more rapidly than 108V, whereas in the presence of 4 mm dithiothreitol (DTT) we found no significant differences in the stability of the two variants at 37 degrees C. DTT also restored most of the activity that was lost upon incubation at 37 degrees C in the absence of DTT. Mass spectrometry showed that cysteines 188 and 191 formed an intramolecular disulfide bond when s-COMT was incubated with oxidized glutathione, whereas cysteines 69, 95, 157, and 173 formed protein-glutathione adducts. Replacing Cys-95 by serine protected 108M s-COMT against inactivation in the absence of a reductant; C33S and Cys-188 mutations had little effect, and C69S was destabilizing. The sequences surrounding the reactive cysteine residues of human s-COMT and other proteins that form glutathione adducts at identified sites all include Pro and/or Gly and most include a hydrogen-bonding residue, suggesting that glutathiolation at conserved sites plays a physiologically important role.
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Affiliation(s)
- Naomi J H Cotton
- Department of Biochemistry, University of Washington, Seattle, Washington 98195-7350, USA
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314
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Deng L, Starostina NG, Liu ZJ, Rose JP, Terns RM, Terns MP, Wang BC. Structure determination of fibrillarin from the hyperthermophilic archaeon Pyrococcus furiosus. Biochem Biophys Res Commun 2004; 315:726-32. [PMID: 14975761 DOI: 10.1016/j.bbrc.2004.01.114] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2004] [Indexed: 11/30/2022]
Abstract
The methyltransferase fibrillarin is the catalytic component of ribonucleoprotein complexes that direct site-specific methylation of precursor ribosomal RNA and are critical for ribosome biogenesis in eukaryotes and archaea. Here we report the crystal structure of a fibrillarin ortholog from the hyperthermophilic archaeon Pyrococcus furiosus at 1.97A resolution. Comparisons of the X-ray structures of fibrillarin orthologs from Methanococcus jannashii and Archaeoglobus fulgidus reveal nearly identical backbone configurations for the catalytic C-terminal domain with the exception of a unique loop conformation at the S-adenosyl-l-methionine (AdoMet) binding pocket in P. furiosus. In contrast, the N-terminal domains are divergent which may explain why some forms of fibrillarin apparently homodimerize (M. jannashii) while others are monomeric (P. furiosus and A. fulgidus). Three positively charged amino acids surround the AdoMet-binding site and sequence analysis indicates that this is a conserved feature of both eukaryotic and archaeal fibrillarins. We discuss the possibility that these basic residues of fibrillarin are important for RNA-guided rRNA methylation.
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Affiliation(s)
- Lu Deng
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, USA
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315
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Forouhar F, Shen J, Xiao R, Acton TB, Montelione GT, Tong L. Functional assignment based on structural analysis: crystal structure of the yggJ protein (HI0303) of Haemophilus influenzae reveals an RNA methyltransferase with a deep trefoil knot. Proteins 2004; 53:329-32. [PMID: 14517985 DOI: 10.1002/prot.10510] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Farhad Forouhar
- Department of Biological Sciences, Northeast Structural Genomics Consortium, Columbia University, New York, New York 10027, USA
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316
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Abstract
Electron micrographs first confirmed that the eukaryotic genome is organized into repeating disk-shaped nucleosomal units composed of histones and their associated DNA. Those images made clear the function of the nucleosome in packaging and condensing the genome. Today, nucleosomes are recognized as highly dynamic units through which the eukaryotic genome can be regulated with epigenetically heritable consequences. This review focuses on the conserved protein structures that mobilize and remodel nucleosomes and specifically mark and recognize their histone and DNA components. These events directly impact DNA transcription, replication, recombination, and repair.
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Affiliation(s)
- Sepideh Khorasanizadeh
- Department of Biochemistry and Molecular Genetics, University of Virginia Health System, Charlottesville, VA 22908, USA.
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317
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Hattman S, Malygin EG. Bacteriophage T2Dam and T4Dam DNA-[N6-adenine]-methyltransferases. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY VOLUME 77 2004; 77:67-126. [PMID: 15196891 DOI: 10.1016/s0079-6603(04)77003-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Stanley Hattman
- Department of Biology, University of Rochester, Rochester, NY 14627-0211 USA
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318
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Abstract
DNA methylation is a common epigenetic modification found in eukaryotic organisms ranging from fungi to mammals. Over the past 15 years, a number of eukaryotic DNA methyltransferases have been identified from various model organisms. These enzymes exhibit distinct biochemical properties and biological functions, partly due to their structural differences. The highly variable N-terminal extensions of these enzymes harbor various evolutionarily conserved domains and motifs, some of which have been shown to be involved in functional specializations. DNA methylation has divergent functions in different organisms, consistent with the notion that it is a dynamically evolving mechanism that can be adapted to fulfill various functions. Genetic studies using model organisms have provided evidence suggesting the progressive integration of DNA methylation into eukaryotic developmental programs during evolution.
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Affiliation(s)
- Taiping Chen
- Cutaneous Biology Research Center, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA
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319
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Elkins PA, Watts JM, Zalacain M, van Thiel A, Vitazka PR, Redlak M, Andraos-Selim C, Rastinejad F, Holmes WM. Insights into catalysis by a knotted TrmD tRNA methyltransferase. J Mol Biol 2003; 333:931-49. [PMID: 14583191 DOI: 10.1016/j.jmb.2003.09.011] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The crystal structure of Escherichia coli tRNA (guanosine-1) methyltransferase (TrmD) complexed with S-adenosyl homocysteine (AdoHcy) has been determined at 2.5A resolution. TrmD, which methylates G37 of tRNAs containing the sequence G36pG37, is a homo-dimer. Each monomer consists of a C-terminal domain connected by a flexible linker to an N-terminal AdoMet-binding domain. The two bound AdoHcy moieties are buried at the bottom of deep clefts. The dimer structure appears integral to the formation of the catalytic center of the enzyme and this arrangement strongly suggests that the anticodon loop of tRNA fits into one of these clefts for methyl transfer to occur. In addition, adjacent hydrophobic sites in the cleft delineate a defined pocket, which may accommodate the GpG sequence during catalysis. The dimer contains two deep trefoil peptide knots and a peptide loop extending from each knot embraces the AdoHcy adenine ring. Mutational analyses demonstrate that the knot is important for AdoMet binding and catalytic activity, and that the C-terminal domain is not only required for tRNA binding but plays a functional role in catalytic activity.
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Affiliation(s)
- Patricia A Elkins
- GlaxoSmithKline, 709 Swedeland Road, UE0447, King of Prussia, PA 19406, USA
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320
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Abstract
Two classes of functional DNA (cytosine-5) methyltransferases have been discovered in mammals to date. One class methylates the unmodified DNA and is designated as the de novo enzyme, whereas the other maintains the methylation status of the daughter strand during DNA replication and thus is referred to as a maintenance DNA methyltransferase. Each enzyme catalyzes methyl group transfer from S-adenosyl-L-methionine to cytosine bases in DNA. During methylation the enzyme flips its target base out of the DNA duplex into a typically concave catalytic pocket. This flipped cytosine base is then a substrate for the enzyme-catalyzed reaction. The newly formed 5-methylcytosine confers epigenetic information on the parental genome without altering nucleotide sequences. This epigenetic information is inherited during DNA replication and cell division. In mammals, DNA methylation participates in gene expression, protection of the genome against selfish DNA, parental imprinting, mammalian X chromosome inactivation, developmental regulation, T cell development, and various diseases.
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321
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Abstract
The enzyme responsible for maintenance methylation of CpG dinucleotides in vertebrates is DNMT1. The presence of DNMT1 in DNA replication foci raises the issue of whether this enzyme needs to gain access to nascent DNA before its packaging into nucleosomes, which occurs very rapidly behind the replication fork. Using nucleosomes positioned along the 5 S rRNA gene, we find that DNMT1 is able to methylate a number of CpG sites even when the DNA major groove is oriented toward the histone surface. However, we also find that the ability of DNMT1 to methylate nucleosomal sites is highly dependent on the nature of the DNA substrate. Although nucleosomes containing the Air promoter are refractory to methylation irrespective of target cytosine location, nucleosomes reconstituted onto the H19 imprinting control region are more accessible. These results argue that although DNMT1 is intrinsically capable of methylating some DNA sequences even after their packaging into nucleosomes, this is not the case for at least a fraction of DNA sequences whose function is regulated by DNA methylation.
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Affiliation(s)
- Mitsuru Okuwaki
- Cancer Research UK, London Research Institute, Clare Hall Laboratories, South Mimms, Hertfordshire EN6 3LD, United Kingdom
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322
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Osipiuk J, Walsh MA, Joachimiak A. Crystal structure of MboIIA methyltransferase. Nucleic Acids Res 2003; 31:5440-8. [PMID: 12954781 PMCID: PMC203307 DOI: 10.1093/nar/gkg713] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2003] [Revised: 06/20/2003] [Accepted: 07/11/2003] [Indexed: 11/14/2022] Open
Abstract
DNA methyltransferases (MTases) are sequence-specific enzymes which transfer a methyl group from S-adenosyl-L-methionine (AdoMet) to the amino group of either cytosine or adenine within a recognized DNA sequence. Methylation of a base in a specific DNA sequence protects DNA from nucleolytic cleavage by restriction enzymes recognizing the same DNA sequence. We have determined at 1.74 A resolution the crystal structure of a beta-class DNA MTase MboIIA (M.MboIIA) from the bacterium Moraxella bovis, the smallest DNA MTase determined to date. M.MboIIA methylates the 3' adenine of the pentanucleotide sequence 5'-GAAGA-3'. The protein crystallizes with two molecules in the asymmetric unit which we propose to resemble the dimer when M.MboIIA is not bound to DNA. The overall structure of the enzyme closely resembles that of M.RsrI. However, the cofactor-binding pocket in M.MboIIA forms a closed structure which is in contrast to the open-form structures of other known MTases.
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Affiliation(s)
- Jerzy Osipiuk
- Argonne National Laboratory, Biosciences Division and Structural Biology Center, 9700 South Cass Avenue, Argonne, IL 60439, USA
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323
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Galimand M, Courvalin P, Lambert T. Plasmid-mediated high-level resistance to aminoglycosides in Enterobacteriaceae due to 16S rRNA methylation. Antimicrob Agents Chemother 2003; 47:2565-71. [PMID: 12878520 PMCID: PMC166065 DOI: 10.1128/aac.47.8.2565-2571.2003] [Citation(s) in RCA: 270] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A self-transferable plasmid of ca. 80 kb, pIP1204, conferred multiple-antibiotic resistance to Klebsiella pneumoniae BM4536, which was isolated from a urinary tract infection. Resistance to beta-lactams was due to the bla(TEM1) and bla(CTX-M) genes, resistance to trimethroprim was due to the dhfrXII gene, resistance to sulfonamides was due to the sul1 gene, resistance to streptomycin-spectinomycin was due to the ant3"9 gene, and resistance to nearly all remaining aminoglycosides was due to the aac3-II gene and a new gene designated armA (aminoglycoside resistance methylase). The cloning of armA into a plasmid in Escherichia coli conferred to the new host high-level resistance to 4,6-disubstituted deoxystreptamines and fortimicin. The deduced sequence of ArmA displayed from 37 to 47% similarity to those of 16S rRNA m(7)G methyltransferases from various actinomycetes, which confer resistance to aminoglycoside-producing strains. However, the low guanine-plus-cytosine content of armA (30%) does not favor an actinomycete origin for the gene. It therefore appears that posttranscriptional modification of 16S rRNA can confer high-level broad-range resistance to aminoglycosides in gram-negative human pathogens.
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Affiliation(s)
- Marc Galimand
- Unité des Agents Antibactériens, Institut Pasteur, 75724 Paris Cedex 15, France.
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324
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Abstract
There is overwhelming evidence that DNA methylation patterns are altered in cancer. Methylation of CG-rich islands in regulatory regions of genes marks them for transcriptional silencing. Multiple genes, which confer selective advantage upon cancer cells such as tumor suppressors, adhesion molecules, inhibitors of angiogenesis and repair enzymes are silenced. In parallel, tumor cell genomes are globally less methylated than their normal counterparts. In contrast to regional hypermethylation, this loss of methylation in cancer cells occurs in sparsely distributed CG sequences. We now understand that DNA methylation machineries might include a number of DNA methyltransferases, proteins that direct DNA methyltransferases to specific promoters, chromatin modifying enzymes as well as demethylases. There is also data to suggest that pharmacological down regulation of some members of the DNA methylation machinery could inhibit cancer in vitro, in vivo and in clinical trials. Understanding which functions of DNA methylation machinery are critical for cancer is essential for the design of inhibitors of the DNA methylation machinery as anticancer agents. This review discusses the possible role of DNA methyltranferases and demethylases in tumorigenesis and the possible pharmacological and therapeutic implications of the DNA methylation machinery.
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Affiliation(s)
- Moshe Szyf
- Department of Pharmacology and Therapeutics, McGill University, 3655 Sir William Osler Promenade, Montreal, Que, Canada H3G 1Y6.
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325
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Zhang X, Yang Z, Khan SI, Horton JR, Tamaru H, Selker EU, Cheng X. Structural basis for the product specificity of histone lysine methyltransferases. Mol Cell 2003; 12:177-85. [PMID: 12887903 PMCID: PMC2713655 DOI: 10.1016/s1097-2765(03)00224-7] [Citation(s) in RCA: 252] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
DIM-5 is a SUV39-type histone H3 Lys9 methyltransferase that is essential for DNA methylation in N. crassa. We report the structure of a ternary complex including DIM-5, S-adenosyl-L-homocysteine, and a substrate H3 peptide. The histone tail inserts as a parallel strand between two DIM-5 strands, completing a hybrid sheet. Three post-SET cysteines coordinate a zinc atom together with Cys242 from the SET signature motif (NHXCXPN) near the active site. Consequently, a narrow channel is formed to accommodate the target Lys9 side chain. The sulfur atom of S-adenosyl-L-homocysteine, where the transferable methyl group is to be attached in S-adenosyl-L-methionine, lies at the opposite end of the channel, approximately 4 A away from the target Lys9 nitrogen. Structural comparison of the active sites of DIM-5, an H3 Lys9 trimethyltransferase, and SET7/9, an H3 Lys4 monomethyltransferase, allowed us to design substitutions in both enzymes that profoundly alter their product specificities without affecting their catalytic activities.
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Affiliation(s)
- Xing Zhang
- Department of Biochemistry, Emory University School of Medicine, 1510 Clifton Road, Atlanta, Georgia 30322
| | - Zhe Yang
- Department of Biochemistry, Emory University School of Medicine, 1510 Clifton Road, Atlanta, Georgia 30322
| | - Seema I. Khan
- Department of Biochemistry, Emory University School of Medicine, 1510 Clifton Road, Atlanta, Georgia 30322
| | - John R. Horton
- Department of Biochemistry, Emory University School of Medicine, 1510 Clifton Road, Atlanta, Georgia 30322
| | - Hisashi Tamaru
- Institute of Molecular Biology, University of Oregon, 1370 Franklin Boulevard, Eugene, Oregon 97403
| | - Eric U. Selker
- Institute of Molecular Biology, University of Oregon, 1370 Franklin Boulevard, Eugene, Oregon 97403
| | - Xiaodong Cheng
- Department of Biochemistry, Emory University School of Medicine, 1510 Clifton Road, Atlanta, Georgia 30322
- Correspondence:
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326
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Reither S, Li F, Gowher H, Jeltsch A. Catalytic mechanism of DNA-(cytosine-C5)-methyltransferases revisited: covalent intermediate formation is not essential for methyl group transfer by the murine Dnmt3a enzyme. J Mol Biol 2003; 329:675-84. [PMID: 12787669 DOI: 10.1016/s0022-2836(03)00509-6] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Co-transfections of reporter plasmids and plasmids encoding the catalytic domain of the murine Dnmt3a DNA methyltransferase lead to inhibition of reporter gene expression. As Dnmt3a mutants with C-->A and E-->A exchanges in the conserved PCQ and ENV motifs in the catalytic center of the enzyme also cause repression, we checked for their catalytic activity in vitro. Surprisingly, the activity of the cysteine variant and of the corresponding full-length Dnmt3a variant is only two to sixfold reduced with respect to wild-type Dnmt3a. In contrast, enzyme variants carrying E-->A, E-->D or E-->Q exchanges of the ENV glutamate are catalytically almost inactive, demonstrating that this residue has a central function in catalysis. Since the glutamic acid residue contacts the flipped base, its main function could be to hold the target base at a position that supports methyl group transfer. Whereas wild-type Dnmt3a and the ENV variants form covalent complexes with 5-fluorocytidine modified DNA, the PCN variant does not. Therefore, covalent complex formation is not essential in the reaction mechanism of Dnmt3a. We propose that correct positioning of the flipped base and the cofactor and binding to the transition state of methyl group transfer are the most important roles of the Dnmt3a enzyme in the catalytic cycle of methyl group transfer.
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Affiliation(s)
- Sabine Reither
- Institut für Biochemie, FB 8, Justus-Liebig Universität, Heinrich-Buff-Ring 58, 35392, Giessen, Germany
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327
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Detich N, Hamm S, Just G, Knox JD, Szyf M. The methyl donor S-Adenosylmethionine inhibits active demethylation of DNA: a candidate novel mechanism for the pharmacological effects of S-Adenosylmethionine. J Biol Chem 2003; 278:20812-20. [PMID: 12676953 DOI: 10.1074/jbc.m211813200] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
S-Adenosylmethionine (AdoMet) is the methyl donor of numerous methylation reactions. The current model is that an increased concentration of AdoMet stimulates DNA methyltransferase reactions, triggering hypermethylation and protecting the genome against global hypomethylation, a hallmark of cancer. Using an assay of active demethylation in HEK 293 cells, we show that AdoMet inhibits active demethylation and expression of an ectopically methylated CMV-GFP (green fluorescent protein) plasmid in a dose-dependent manner. The inhibition of GFP expression is specific to methylated GFP; AdoMet does not inhibit an identical but unmethylated CMV-GFP plasmid. S-Adenosylhomocysteine (AdoHcy), the product of methyltransferase reactions utilizing AdoMet does not inhibit demethylation or expression of CMV-GFP. In vitro, AdoMet but not AdoHcy inhibits methylated DNA-binding protein 2/DNA demethylase as well as endogenous demethylase activity extracted from HEK 293, suggesting that AdoMet directly inhibits demethylase activity, and that the methyl residue on AdoMet is required for its interaction with demethylase. Taken together, our data support an alternative mechanism of action for AdoMet as an inhibitor of intracellular demethylase activity, which results in hypermethylation of DNA.
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Affiliation(s)
- Nancy Detich
- Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec H3G 1YG, Canada
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328
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Abstract
S-adenosyl-L-methionine (AdoMet) dependent methyltransferases (MTases) are involved in biosynthesis, signal transduction, protein repair, chromatin regulation and gene silencing. Five different structural folds (I-V) have been described that bind AdoMet and catalyze methyltransfer to diverse substrates, although the great majority of known MTases have the Class I fold. Even within a particular MTase class the amino-acid sequence similarity can be as low as 10%. Thus, the structural and catalytic requirements for methyltransfer from AdoMet appear to be remarkably flexible.
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Affiliation(s)
- Heidi L. Schubert
- Department of Biochemistry, University of Utah, Salt Lake City, UT 84132-201, USA
| | - Robert M. Blumenthal
- Department of Microbiology and Immunology and Program in Bioinformatics and Proteomics/Genomics, Medical College of Ohio, Toledo, OH 43614-806, USA
| | - Xiaodong Cheng
- Department of Biochemistry, Emory University School of Medicine Atlanta, GA 30322, USA
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329
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Mosbacher TG, Bechthold A, Schulz GE. Crystal structure of the avilamycin resistance-conferring methyltransferase AviRa from Streptomyces viridochromogenes. J Mol Biol 2003; 329:147-57. [PMID: 12742024 DOI: 10.1016/s0022-2836(03)00407-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The emergence of antibiotic-resistant bacterial strains is a widespread problem in contemporary medical practice and drug design. It is therefore important to elucidate the underlying mechanism in each case. The methyltransferase AviRa from Streptomyces viridochromogenes mediates resistance to the antibiotic avilamycin, which is closely related to evernimicin, an oligosaccharide antibiotic that has been used in medical studies. The structure of AviRa was determined by X-ray diffraction at 1.5A resolution. Phases were obtained from one selenomethionine residue introduced by site-directed mutagenesis. The chain-fold is similar to that of most methyltransferases, although AviRa contains two additional helices as a specific feature. A putative-binding site for the cofactor S-adenosyl-L-methionine was derived from homologous structures. It agrees with the conserved pattern of interacting amino acid residues. AviRa methylates a specific guanine base within the peptidyltransferase loop of the 23S ribosomal RNA. Guided by the target, the enzyme was docked to the cognate ribosomal surface, where it fit well into a deep cleft without contacting any ribosomal protein. The two additional alpha-helices of AviRa filled a depression in the surface. Since the transferred methyl group of the cofactor is in a pocket beneath the enzyme surface, the targeted guanine base has to flip out for methylation.
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Affiliation(s)
- Tanja G Mosbacher
- Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Albertstr. 21, Freiburg im Breisgau, 79104, Germany
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330
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Zhang X, Cheng X. Structure of the predominant protein arginine methyltransferase PRMT1 and analysis of its binding to substrate peptides. Structure 2003; 11:509-20. [PMID: 12737817 PMCID: PMC4030380 DOI: 10.1016/s0969-2126(03)00071-6] [Citation(s) in RCA: 275] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PRMT1 is the predominant type I protein arginine methyltransferase in mammals and highly conserved among all eukaryotes. It is essential for early postimplantation development in mouse. Here we describe the crystal structure of rat PRMT1 in complex with the reaction product AdoHcy and a 19 residue substrate peptide containing three arginines. The results reveal a two-domain structure-an AdoMet binding domain and a barrel-like domain-with the active site pocket located between the two domains. Mutagenesis studies confirmed that two active site glutamates are essential for enzymatic activity, and that dimerization of PRMT1 is essential for AdoMet binding. Three peptide binding channels are identified: two are between the two domains, and the third is on the surface perpendicular to the strands forming the beta barrel.
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331
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Shepherd M, Reid JD, Hunter CN. Purification and kinetic characterization of the magnesium protoporphyrin IX methyltransferase from Synechocystis PCC6803. Biochem J 2003; 371:351-60. [PMID: 12489983 PMCID: PMC1223276 DOI: 10.1042/bj20021394] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2002] [Revised: 11/21/2002] [Accepted: 12/18/2002] [Indexed: 11/17/2022]
Abstract
Magnesium protoporphyrin IX methyltransferase (ChlM), catalyses the methylation of magnesium protoporphyrin IX (MgP) at the C(6) propionate side chain to form magnesium protoporphyrin IX monomethylester (MgPME). Threading methods biased by sequence similarity and predicted secondary structure have been used to assign this enzyme to a particular class of S-adenosyl-L-methionine (SAM)-binding proteins. These searches suggest that ChlM contains a seven-stranded beta-sheet, common among small-molecule methyltransferases. Steady-state kinetic assays were performed using magnesium deuteroporphyrin IX (MgD), a more water-soluble substrate analogue of MgP. Initial rate studies showed that the reaction proceeds via a ternary complex. Product (S-adenosyl-L-homocysteine; SAH) inhibition was used to investigate the kinetic mechanism further. SAH was shown to exhibit competitive inhibition with respect to SAM, and mixed inhibition with respect to MgD. This is indicative of a random binding mechanism, whereby SAH may bind productively to either free enzyme or a ChlM-MgD complex. Our results provide an overview of the steady-state kinetics for this enzyme, which are significant given the role of MgP and MgPME in plastid-to-nucleus signalling and their likely critical role in the regulation of this biosynthetic pathway.
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Affiliation(s)
- Mark Shepherd
- Robert Hill Institute for Photosynthesis, Department of Molecular Biology and Biotechnology, Firth Court, Western Bank, University of Sheffield, Sheffield S10 2TN, UK
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332
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Aittaleb M, Rashid R, Chen Q, Palmer JR, Daniels CJ, Li H. Structure and function of archaeal box C/D sRNP core proteins. Nat Struct Mol Biol 2003; 10:256-63. [PMID: 12598892 DOI: 10.1038/nsb905] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2002] [Accepted: 01/03/2003] [Indexed: 11/09/2022]
Abstract
Nop56p and Nop58p are two core proteins of the box C/D snoRNPs that interact concurrently with fibrillarin and snoRNAs to function in enzyme assembly and catalysis. Here we report the 2.9 A resolution co-crystal structure of an archaeal homolog of Nop56p/Nop58p, Nop5p, in complex with fibrillarin from Archaeoglobus fulgidus (AF) and the methyl donor S-adenosyl-L-methionine. The N-terminal domain of Nop5p forms a complementary surface to fibrillarin that serves to anchor the catalytic subunit and to stabilize cofactor binding. A coiled coil in Nop5p mediates dimerization of two fibrillarin-Nop5p heterodimers for optimal interactions with bipartite box C/D RNAs. Structural analysis and complementary biochemical data demonstrate that the conserved C-terminal domain of Nop5p harbors RNA-binding sites. A model of box C/D snoRNP assembly is proposed based on the presented structural and biochemical data.
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MESH Headings
- Amino Acid Sequence
- Archaeal Proteins/chemistry
- Archaeal Proteins/genetics
- Archaeal Proteins/metabolism
- Archaeoglobus fulgidus/genetics
- Archaeoglobus fulgidus/metabolism
- Binding Sites
- Chromosomal Proteins, Non-Histone/chemistry
- Chromosomal Proteins, Non-Histone/metabolism
- Crystallography, X-Ray
- Dimerization
- Electrophoretic Mobility Shift Assay
- Macromolecular Substances
- Models, Molecular
- Molecular Sequence Data
- Molecular Structure
- Nuclear Proteins
- Protein Structure, Tertiary
- RNA Editing
- RNA, Archaeal/chemistry
- RNA, Archaeal/genetics
- RNA, Archaeal/metabolism
- RNA, Small Nucleolar/chemistry
- RNA, Small Nucleolar/genetics
- RNA, Small Nucleolar/metabolism
- Ribonucleoproteins, Small Nucleolar/chemistry
- Ribonucleoproteins, Small Nucleolar/genetics
- Ribonucleoproteins, Small Nucleolar/metabolism
- Sequence Homology, Amino Acid
- Static Electricity
- RNA, Small Untranslated
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Affiliation(s)
- Mohamed Aittaleb
- Department of Chemistry and Biochemistry, Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306, USA
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333
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Daujotyte D, Vilkaitis G, Manelyte L, Skalicky J, Szyperski T, Klimasauskas S. Solubility engineering of the HhaI methyltransferase. Protein Eng Des Sel 2003; 16:295-301. [PMID: 12736373 DOI: 10.1093/proeng/gzg034] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
DNA methylation is involved in epigenetic control of numerous cellular processes in eukaryotes, however, many mechanistic aspects of this phenomenon are not yet understood. A bacterial prototype cytosine-C5 methyltransferase, M.HhaI, serves as a paradigm system for structural and mechanistic studies of biological DNA methylation, but further analysis of the 37 kDa protein is hampered by its insufficient solubility (0.15 mM). To overcome this problem, three hydrophobic patches on the surface of M.HhaI that are not involved in substrate interactions were subjected to site-specific mutagenesis. Residues M51 or V213 were substituted by polar amino acids of a similar size, and/or the C-terminal tetrapeptide FKPY was replaced by a single glycine residue (Delta324G). Two out of six mutants, delta324G and V213S/delta324G, showed improved solubility in initial analyses and were purified to homogeneity using a newly developed procedure. Biochemical studies of the engineered methyltransferases showed that the deletion mutant delta324G retained identical DNA binding, base flipping and catalytic properties as the wild-type enzyme. In contrast, the engineered enzyme showed (i) a significantly increased solubility (>0.35 mM), (ii) high-quality 2D-[(15)N,(1)H] TROSY NMR spectra, and (iii) (15)N spin relaxation times evidencing the presence of a monomeric well-folded protein in solution.
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Affiliation(s)
- Dalia Daujotyte
- Laboratory of Biological DNA Modification, Institute of Biotechnology, LT-2028 Vilnius, Lithuania
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334
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Abstract
Most 5-methylcytosine in Neurospora crassa occurs in A:T-rich sequences high in TpA dinucleotides, hallmarks of repeat-induced point mutation. To investigate how such sequences induce methylation, we developed a sensitive in vivo system. Tests of various 25- to 100-bp synthetic DNA sequences revealed that both T and A residues were required on a given strand to induce appreciable methylation. Segments composed of (TAAA)(n) or (TTAA)(n) were the most potent signals; 25-mers induced robust methylation at the special test site, and a 75-mer induced methylation elsewhere. G:C base pairs inhibited methylation, and cytosines 5' of ApT dinucleotides were particularly inhibitory. Weak signals could be strengthened by extending their lengths. A:T tracts as short as two were found to cooperate to induce methylation. Distamycin, which, like the AT-hook DNA binding motif found in proteins such as mammalian HMG-I, binds to the minor groove of A:T-rich sequences, suppressed DNA methylation and gene silencing. We also found a correlation between the strength of methylation signals and their binding to an AT-hook protein (HMG-I) and to activities in a Neurospora extract. We propose that de novo DNA methylation in Neurospora cells is triggered by cooperative recognition of the minor groove of multiple short A:T tracts. Similarities between sequences subjected to repeat-induced point mutation in Neurospora crassa and A:T-rich repeated sequences in heterochromatin in other organisms suggest that related mechanisms control silent chromatin in fungi, plants, and animals.
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Affiliation(s)
- Hisashi Tamaru
- Department of Biology and Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403-1229, USA
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335
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Min J, Feng Q, Li Z, Zhang Y, Xu RM. Structure of the catalytic domain of human DOT1L, a non-SET domain nucleosomal histone methyltransferase. Cell 2003; 112:711-23. [PMID: 12628190 DOI: 10.1016/s0092-8674(03)00114-4] [Citation(s) in RCA: 288] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Dot1 is an evolutionarily conserved histone methyltransferase that methylates lysine-79 of histone H3 in the core domain. Unlike other histone methyltransferases, Dot1 does not contain a SET domain, and it specifically methylates nucleosomal histone H3. We have solved a 2.5 A resolution structure of the catalytic domain of human Dot1, hDOT1L, in complex with S-adenosyl-L-methionine (SAM). The structure reveals a unique organization of a mainly alpha-helical N-terminal domain and a central open alpha/beta structure, an active site consisting of a SAM binding pocket, and a potential lysine binding channel. We also show that a flexible, positively charged region at the C terminus of the catalytic domain is critical for nucleosome binding and enzymatic activity. These structural and biochemical analyses, combined with molecular modeling, provide mechanistic insights into the catalytic mechanism and nucleosomal specificity of Dot1 proteins.
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Affiliation(s)
- Jinrong Min
- W.M. Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
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336
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Humeny A, Beck C, Becker CM, Jeltsch A. Detection and analysis of enzymatic DNA methylation of oligonucleotide substrates by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Anal Biochem 2003; 313:160-6. [PMID: 12576072 DOI: 10.1016/s0003-2697(02)00568-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF) mass spectrometry was employed to analyze DNA methylation carried out by the Escherichia coli dam DNA methyltransferase using oligonucleotide substrates with molecular masses of 5000-10,000 Da per strand. The mass spectrometry assay offers several advantages: (i) it directly shows the methylation as the increase in the mass of the substrate DNA, (ii) it is nonradioactive, (iii) it is quantitative, and (iv) it can be automated for high-throughput applications. Since unmethylated and methylated DNA are detected, the ratio of methylation can be determined directly and accurately. Furthermore, the assay allows detection individually of the methylation of several substrates in competition, offering an ideal setup to analyze the specificity of DNA interacting with enzymes. We could not identify methylation at any noncanonical site, indicating that the dam MTase is a very specific enzyme. Finally, MALDI-TOF mass spectrometry permitted assessment of the number of methyl groups incorporated into each DNA strand, thereby, allowing study of mechanistic details such as the processivity of the methylation reaction. We provide evidence that the dam MTase modifies DNA in a processive reaction, confirming earlier findings.
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Affiliation(s)
- Andreas Humeny
- Institut für Biochemie, Emil-Fischer-Zentrum, Friedrich-Alexander Universität Erlangen-Nürnberg, Fahrstrasse 17, 91054 Erlangen, Germany
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337
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Huang N, Banavali NK, MacKerell AD. Protein-facilitated base flipping in DNA by cytosine-5-methyltransferase. Proc Natl Acad Sci U S A 2003; 100:68-73. [PMID: 12506195 PMCID: PMC140885 DOI: 10.1073/pnas.0135427100] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
DNA methylation, various DNA repair mechanisms, and possibly early events in the opening of DNA as required for transcription and replication are initiated by flipping of a DNA base out of the DNA double helix. The energetics and structural mechanism of base flipping in the presence of the DNA-processing enzyme, cytosine 5-methyltransferase from HhaI (M.HhaI), were obtained through molecular dynamics based upon free-energy calculations. Free-energy profiles for base flipping show that, when in the closed conformation, M.HhaI lowers the free-energy barrier to flipping by 17 kcalmol and stabilizes the fully flipped state. Flipping is shown to occur via the major groove of the DNA. Structural analysis indicates that flipping is facilitated by destabilization of the DNA double-helical structure and substitution of DNA base-pairing and base-stacking interactions with DNA-protein interactions. The fully flipped state is stabilized by DNA-protein interactions that are enhanced upon binding of coenzyme. This study represents an atomic detail description of the mechanism by which a protein facilitates specific structural distortion in DNA.
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Affiliation(s)
- Niu Huang
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
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338
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Sedgwick B, Lindahl T. Recent progress on the Ada response for inducible repair of DNA alkylation damage. Oncogene 2002; 21:8886-94. [PMID: 12483506 DOI: 10.1038/sj.onc.1205998] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Barbara Sedgwick
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Hertfordshire EN6 3LD, UK
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339
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Larivière L, Moréra S. A base-flipping mechanism for the T4 phage beta-glucosyltransferase and identification of a transition-state analog. J Mol Biol 2002; 324:483-90. [PMID: 12445783 DOI: 10.1016/s0022-2836(02)01091-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
T4 phage beta-glucosyltransferase (BGT) modifies T4 DNA. We crystallized BGT with UDP-glucose and a 13mer DNA fragment containing an abasic site. We obtained two crystal structures of a ternary complex BGT-UDP-DNA at 1.8A and 2.5A resolution, one with a Tris molecule and the other with a metal ion at the active site. Both structures reveal a large distortion in the bound DNA. BGT flips the deoxyribose moiety at the abasic site to an extra-helical position and induces a 40 degrees bend in the DNA with a marked widening of the major groove. The Tris molecule mimics the glucose moiety in its transition state. The base-flipping mechanism, which has so far been observed only for glycosylases, methyltransferases and endonucleases, is now reported for a glucosyltransferase. BGT is unique in binding and inserting a loop into the DNA duplex through the major groove only. Furthermore, BGT compresses the backbone DNA one base further than the target base on the 3'-side.
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Affiliation(s)
- Laurent Larivière
- Laboratoire d'Enzymologie et Biochimie Structurales, UPR 9063 CNRS, Bât. 34, 1 Avenue de la Terrasse, 91198, Gif-sur-Yvette, France
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340
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Wilson JR, Jing C, Walker PA, Martin SR, Howell SA, Blackburn GM, Gamblin SJ, Xiao B. Crystal structure and functional analysis of the histone methyltransferase SET7/9. Cell 2002; 111:105-15. [PMID: 12372304 DOI: 10.1016/s0092-8674(02)00964-9] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Methylation of lysine residues in the N-terminal tails of histones is thought to represent an important component of the mechanism that regulates chromatin structure. The evolutionarily conserved SET domain occurs in most proteins known to possess histone lysine methyltransferase activity. We present here the crystal structure of a large fragment of human SET7/9 that contains a N-terminal beta-sheet domain as well as the conserved SET domain. Mutagenesis identifies two residues in the C terminus of the protein that appear essential for catalytic activity toward lysine-4 of histone H3. Furthermore, we show how the cofactor AdoMet binds to this domain and present biochemical data supporting the role of invariant residues in catalysis, binding of AdoMet, and interactions with the peptide substrate.
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Affiliation(s)
- Jonathan R Wilson
- Structural Biology Group, National Institute for Medical Research, The Ridgeway, Mill Hill, London, United Kingdom
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341
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Abstract
Proteins bearing the widely distributed SET domain have been shown to methylate lysine residues in histones and other proteins. In this issue, three-dimensional structures are reported for three very different SET domain-containing proteins. The structures reveal novel folds for several new domains, including SET, and provide early insights into mechanisms of catalysis and molecular recognition in this family of enzymes.
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Affiliation(s)
- Todd O Yeates
- UCLA Molecular Biology Institute and Department of Chemistry and Biochemistry, UCLA-DOE Center for Genomics and Proteomics, 611 Charles Young Dr. East, Box 951570, Los Angeles, CA 90095, USA.
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342
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Zhang X, Tamaru H, Khan SI, Horton JR, Keefe LJ, Selker EU, Xiaodong C. Structure of the Neurospora SET domain protein DIM-5, a histone H3 lysine methyltransferase. Cell 2002; 111:117-27. [PMID: 12372305 PMCID: PMC2713760 DOI: 10.1016/s0092-8674(02)00999-6] [Citation(s) in RCA: 202] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
AdoMet-dependent methylation of histones is part of the "histone code" that can profoundly influence gene expression. We describe the crystal structure of Neurospora DIM-5, a histone H3 lysine 9 methyltranferase (HKMT), determined at 1.98 A resolution, as well as results of biochemical characterization and site-directed mutagenesis of key residues. This SET domain protein bears no structural similarity to previously characterized AdoMet-dependent methyltransferases but includes notable features such as a triangular Zn3Cys9 zinc cluster in the pre-SET domain and a AdoMet binding site in the SET domain essential for methyl transfer. The structure suggests a mechanism for the methylation reaction and provides the structural basis for functional characterization of the HKMT family and the SET domain.
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Affiliation(s)
- Xing Zhang
- Department of Biochemistry, School of Medicine, Emory University, 1510 Clifton Road, Atlanta, Georgia 30322
| | - Hisashi Tamaru
- Institute of Molecular Biology, University of Oregon, 1370 Franklin Boulevard, Eugene, Oregon 97403
| | - Seema I. Khan
- Department of Biochemistry, School of Medicine, Emory University, 1510 Clifton Road, Atlanta, Georgia 30322
| | - John R. Horton
- Department of Biochemistry, School of Medicine, Emory University, 1510 Clifton Road, Atlanta, Georgia 30322
| | - Lisa J. Keefe
- Advanced Photon Source (IMCA-CAT), Sector 17, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
| | - Eric U. Selker
- Institute of Molecular Biology, University of Oregon, 1370 Franklin Boulevard, Eugene, Oregon 97403
| | - Cheng Xiaodong
- Department of Biochemistry, School of Medicine, Emory University, 1510 Clifton Road, Atlanta, Georgia 30322
- Correspondence:
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343
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Fatemi M, Hermann A, Gowher H, Jeltsch A. Dnmt3a and Dnmt1 functionally cooperate during de novo methylation of DNA. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:4981-4. [PMID: 12383256 DOI: 10.1046/j.1432-1033.2002.03198.x] [Citation(s) in RCA: 177] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Dnmt3a is a de novo DNA methyltransferase that modifies unmethylated DNA. In contrast Dnmt1 shows high preference for hemimethylated DNA. However, Dnmt1 can be activated for the methylation of unmodified DNA. We show here that the Dnmt3a and Dnmt1 DNA methyltransferases functionally cooperate in de novo methylation of DNA, because a fivefold stimulation of methylation activity is observed if both enzymes are present. Stimulation is observed if Dnmt3a is used before Dnmt1, but not if incubation with Dnmt1 precedes Dnmt3a, demonstrating that methylation of the DNA by Dnmt3a stimulates Dnmt1 and that no physical interaction of Dnmt1 and Dnmt3a is required. If Dnmt1 and Dnmt3a were incubated together a slightly increased stimulation is observed that could be due to a direct interaction of these enzymes. In addition, we show that Dnmt1 is stimulated for methylation of unmodified DNA if the DNA already carries some methyl groups. We conclude that after initiation of de novo methylation of DNA by Dnmt3a, Dnmt1 becomes activated by the pre-existing methyl groups and further methylates the DNA. Our data suggest that Dnmt1 also has a role in de novo methylation of DNA. This model agrees with the biochemical properties of these enzymes and provides a mechanistic basis for the functional cooperation of different DNA MTases in de novo methylation of DNA that has also been observed in vivo.
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Affiliation(s)
- Mehrnaz Fatemi
- Institut für Biochemie, Justus-Liebig-Universität, Giessen, Germany
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344
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Abstract
DNA methyltransferases catalyze the transfer of a methyl group from S-adenosyl-L-methionine to cytosine or adenine bases in DNA. These enzymes challenge the Watson/Crick dogma in two instances: 1) They attach inheritable information to the DNA that is not encoded in the nucleotide sequence. This so-called epigenetic information has many important biological functions. In prokaryotes, DNA methylation is used to coordinate DNA replication and the cell cycle, to direct postreplicative mismatch repair, and to distinguish self and nonself DNA. In eukaryotes, DNA methylation contributes to the control of gene expression, the protection of the genome against selfish DNA, maintenance of genome integrity, parental imprinting, X-chromosome inactivation in mammals, and regulation of development. 2) The enzymatic mechanism of DNA methyltransferases is unusual, because these enzymes flip their target base out of the DNA helix and, thereby, locally disrupt the B-DNA helix. This review describes the biological functions of DNA methylation in bacteria, fungi, plants, and mammals. In addition, the structures and mechanisms of the DNA methyltransferases, which enable them to specifically recognize their DNA targets and to induce such large conformational changes of the DNA, are discussed.
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Affiliation(s)
- Albert Jeltsch
- Institut für Biochemie, FB 8, Justus-Liebig-Universität, Heinrich-Buff-Ring 58, 35392 Giessen, Germany.
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345
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Zhou L, Cheng X, Connolly B, Dickman M, Hurd P, Hornby D. Zebularine: a novel DNA methylation inhibitor that forms a covalent complex with DNA methyltransferases. J Mol Biol 2002; 321:591-9. [PMID: 12206775 PMCID: PMC2713825 DOI: 10.1016/s0022-2836(02)00676-9] [Citation(s) in RCA: 237] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Mechanism-based inhibitors of enzymes, which mimic reactive intermediates in the reaction pathway, have been deployed extensively in the analysis of metabolic pathways and as candidate drugs. The inhibition of cytosine-[C5]-specific DNA methyltransferases (C5 MTases) by oligodeoxynucleotides containing 5-azadeoxycytidine (AzadC) and 5-fluorodeoxycytidine (FdC) provides a well-documented example of mechanism-based inhibition of enzymes central to nucleic acid metabolism. Here, we describe the interaction between the C5 MTase from Haemophilus haemolyticus (M.HhaI) and an oligodeoxynucleotide duplex containing 2-H pyrimidinone, an analogue often referred to as zebularine and known to give rise to high-affinity complexes with MTases. X-ray crystallography has demonstrated the formation of a covalent bond between M.HhaI and the 2-H pyrimidinone-containing oligodeoxynucleotide. This observation enables a comparison between the mechanisms of action of 2-H pyrimidinone with other mechanism-based inhibitors such as FdC. This novel complex provides a molecular explanation for the mechanism of action of the anti-cancer drug zebularine.
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Affiliation(s)
- L. Zhou
- Department of Biochemistry, Emory University School of Medicine, 1510 Clifton Road, Atlanta, GA 30322, USA
| | - X. Cheng
- Department of Biochemistry, Emory University School of Medicine, 1510 Clifton Road, Atlanta, GA 30322, USA
| | - B.A. Connolly
- Department of Biochemistry and Genetics, University of Newcastle, Newcastle-upon-Tyne NE2, 4HH, UK
| | - M.J. Dickman
- Krebs Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, P.O. Box 594, First Court, Western Bank, Sheffield, S10 2TN, UK
| | - P.J. Hurd
- Wellcome/CRC Institute of Cancer and Developmental Biology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
| | - D.P. Hornby
- Krebs Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, P.O. Box 594, First Court, Western Bank, Sheffield, S10 2TN, UK
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346
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Christman JK. 5-Azacytidine and 5-aza-2'-deoxycytidine as inhibitors of DNA methylation: mechanistic studies and their implications for cancer therapy. Oncogene 2002; 21:5483-95. [PMID: 12154409 DOI: 10.1038/sj.onc.1205699] [Citation(s) in RCA: 1009] [Impact Index Per Article: 45.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
5-Azacytidine was first synthesized almost 40 years ago. It was demonstrated to have a wide range of anti-metabolic activities when tested against cultured cancer cells and to be an effective chemotherapeutic agent for acute myelogenous leukemia. However, because of 5-azacytidine's general toxicity, other nucleoside analogs were favored as therapeutics. The finding that 5-azacytidine was incorporated into DNA and that, when present in DNA, it inhibited DNA methylation, led to widespread use of 5-azacytidine and 5-aza-2'-deoxycytidine (Decitabine) to demonstrate the correlation between loss of methylation in specific gene regions and activation of the associated genes. There is now a revived interest in the use of Decitabine as a therapeutic agent for cancers in which epigenetic silencing of critical regulatory genes has occurred. Here, the current status of our understanding of the mechanism(s) by which 5-azacytosine residues in DNA inhibit DNA methylation is reviewed with an emphasis on the interactions of these residues with bacterial and mammalian DNA (cytosine-C5) methyltransferases. The implications of these mechanistic studies for development of less toxic inhibitors of DNA methylation are discussed.
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Affiliation(s)
- Judith K Christman
- Department of Biochemistry and Molecular Biology and UNMC/Eppley Cancer Center, University of Nebraska Medical Center, 984525 University Medical Center, Omaha, Nebraska, NE 68198-4525, USA.
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347
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348
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Várnai P, Lavery R. Base flipping in DNA: pathways and energetics studied with molecular dynamic simulations. J Am Chem Soc 2002; 124:7272-3. [PMID: 12071727 DOI: 10.1021/ja025980x] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Carrying out chemistry on the bases of DNA, necessary for biological processes such as methylation or repair, requires flipping the base into an accessible position. In this work, molecular dynamics simulations are used to generate a free energy profile for flipping a cytosine base out of its helical stack in double-stranded DNA. The results shed light on the mechanics of this process by comparing routes for base flipping via the minor and major grooves.
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Affiliation(s)
- Péter Várnai
- Laboratoire de Biochimie Théorique, CNRS UPR 9080, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, Paris 75005, France
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349
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Urig S, Gowher H, Hermann A, Beck C, Fatemi M, Humeny A, Jeltsch A. The Escherichia coli dam DNA methyltransferase modifies DNA in a highly processive reaction. J Mol Biol 2002; 319:1085-96. [PMID: 12079349 DOI: 10.1016/s0022-2836(02)00371-6] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The Escherichia coli dam adenine-N6 methyltransferase modifies DNA at GATC sequences. It is involved in post-replicative mismatch repair, control of DNA replication and gene regulation. We show that E. coli dam acts as a functional monomer and methylates only one strand of the DNA in each binding event. The preferred way of ternary complex assembly is that the enzyme first binds to DNA and then to S-adenosylmethionine. The enzyme methylates an oligonucleotide containing two dam sites and a 879 bp PCR product with four sites in a fully processive reaction. On lambda-DNA comprising 48,502 bp and 116 dam sites, E. coli dam scans 3000 dam sites per binding event in a random walk, that on average leads to a processive methylation of 55 sites. Processive methylation of DNA considerably accelerates DNA methylation. The highly processive mechanism of E. coli dam could explain why small amounts of E. coli dam are able to maintain the methylation state of dam sites during DNA replication. Furthermore, our data support the general rule that solitary DNA methyltransferase modify DNA processively whereas methyltransferases belonging to a restriction-modification system show a distributive mechanism, because processive methylation of DNA would interfere with the biological function of restriction-modification systems.
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Affiliation(s)
- Sabine Urig
- Institut für Biochemie, Fachbereich Biologie, Justus-Liebig-Universität, Heinrich-Buff-Ring 58, 35392 Giessen, Germany
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350
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Gowher H, Jeltsch A. Molecular enzymology of the catalytic domains of the Dnmt3a and Dnmt3b DNA methyltransferases. J Biol Chem 2002; 277:20409-14. [PMID: 11919202 DOI: 10.1074/jbc.m202148200] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The C-terminal domains of the mammalian DNA methyltransferases Dnmt1, Dnmt3a, and Dnmt3b harbor all the conserved motifs characteristic for cytosine-C5 methyltransferases. Whereas the isolated catalytic domain of Dnmt1 is inactive, we show here that the C-terminal domains of Dnmt3a and Dnmt3b are catalytically active. Neither Dnmt3a nor Dnmt3b shows a significant preference for the satellite 2 sequence, although Dnmt3b is required for methylation of these regions in vivo. However, the catalytic domain of Dnmt3a methylates DNA in a distributive reaction, whereas Dnmt3b is processive, which accelerates methylation of macromolecular DNA in vitro. This property could make Dnmt3b a preferred enzyme for methylation at satellite 2 repeats, since they are highly CG-rich. We have also analyzed the catalytic activities of six different mutations found in ICF (immunodeficiency, centromeric instability, and facial abnormalities) patients in the catalytic domain of Dnmt3b. Five of them display catalytic activities reduced by 10-50-fold; one mutant was inactive in our assay (residual activity <1%). These results confirm that a reduced catalytic activity of Dnm3b causes ICF. However, the mutations in general do not completely abrogate catalytic activity. This finding may explain why ICF patients are viable, whereas nmt3b knock-out mice die during embryogenesis.
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Affiliation(s)
- Humaira Gowher
- Institut für Biochemie, FB 8, Justus-Liebig-Universität, Heinrich-Buff-Ring 58, 35392 Giessen, Germany
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