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Methyl Transfer (methyl + transfer)
Selected AbstractsThe solution structure of the methylated form of the N-terminal 16-kDa domain of Escherichia coli Ada proteinPROTEIN SCIENCE, Issue 3 2006Hiroto Takinowaki N-Ada16k, the N-terminal 16-kDa domain of the Ada protein; meC38 N-Ada16k, the Cys38 methylated form of N-Ada16k; MTase, methyltransferase; HTH, helix-turn-helix; NMR, nuclear magnetic resonance; MALDI-TOF MS, matrix assisted laser desorption/ionization time of flight mass spectrometry; MNU, methylnitrosourea Abstract The N-terminal 16-kDa domain of Escherichia coli Ada protein (N-Ada16k) repairs DNA methyl phosphotriester lesions by an irreversible methyl transfer to its cysteine residue. Upon the methylation, the sequence-specific DNA binding affinity for the promoter region of the alkylation resistance genes is enhanced by 103 -fold. Then, it acts as a transcriptional regulator for the methylation damage. In this paper, we identified the methyl acceptor residue of N-Ada16k and determined the solution structure of the methylated form of N-Ada16k by using NMR and mass spectrometry. The results of a 13C-filtered 1H- 13C HMBC experiment and MALDI-TOF MS and MS/MS experiments clearly showed that the methyl acceptor residue is Cys38. The solution structure revealed that it has two distinct subdomains connected by a flexible linker loop: the methyltransferase (MTase) subdomain with the zinc,thiolate center, and the helical subdomain with a helix-turn-helix motif. Interestingly, there is no potential hydrogen bond donor around Cys38, whereas the other three cysteine residues coordinated to a zinc ion have potential donors. Hence, Cys38 could retain its inherent nucleophilicity and react with a methyl phosphotriester. Furthermore, the structure comparison shows that there is no indication of a remarkable conformational change occurring upon the methylation. This implies that the electrostatic repulsion between the negatively charged DNA and the zinc,thiolate center may avoid the contact between the MTase subdomain and the DNA in the nonmethylated form. Thus, after the Cys38 methylation, the MTase subdomain can bind the cognate DNA because the negative charge of the zinc,thiolate center is reduced. [source] Topochemically controlled solid-state methyl rearrangement in thiocyanuratesACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2001Mark Greenberg 4,6-Dimethoxy-3-methyl-1,3,5-triazine-2(3H)-thione crystallizes in two polymorphic forms, needles and plates. In the needle-shaped crystals (9a) the molecules occupy the crystallographic mirror plane, thus the layers are stacked along the b axis. The molecules of the other polymorph [plate-shape crystals, (9b)] are packed in a herringbone packing mode. Upon heating, (9b) undergoes a phase transition to form (9a). At 378,K the needles undergo O , S topochemically controlled methyl transfer in the solid state to produce 1-methyl-4-methoxy-6-methylthio-1,3,5-triazine-2(1H)-one in 75% yield. The enthalpy of the rearrangement is estimated to be ,39.1,kJ,mol,1. 1-Methyl-6-methoxy-4-methylthio-1,3,5-triazine-2(1H)-thione crystallizes in space group P21 with two crystallographically independent molecules in the asymmetric unit. Compound (9b) undergoes O , S methyl transfer in the solid state at 373,K. The rearrangement is topochemically assisted and the product, 1-methyl-2,4-bismethylthio-1,3,5-triazine-6(1H)-one, is obtained in quantitative yield. The enthalpy of the rearrangement is estimated to be ,58.8,kJ,mol,1. The crystal structures of the compounds as well as their DSC thermographs are described and discussed. Energy calculation by ab initio methods shows that the driving force for the reactions is the difference between the molecular energies of the pre-rearranged compounds and their products, 54.2 and 59.3,kJ,mol,1 in the two cases, respectively. [source] Structures of a putative RNA 5-methyluridine methyltransferase, Thermus thermophilus TTHA1280, and its complex with S -adenosyl- l -homocysteineACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 10 2005Augen A. Pioszak The Thermus thermophilus hypothetical protein TTHA1280 belongs to a family of predicted S -adenosyl- l -methionine (AdoMet) dependent RNA methyltransferases (MTases) present in many bacterial and archaeal species. Inspection of amino-acid sequence motifs common to class I Rossmann-fold-like MTases suggested a specific role as an RNA 5-methyluridine MTase. Selenomethionine (SeMet) labelled and native versions of the protein were expressed, purified and crystallized. Two crystal forms of the SeMet-labelled apoprotein were obtained: SeMet-ApoI and SeMet-ApoII. Cocrystallization of the native protein with S -adenosyl- l -homocysteine (AdoHcy) yielded a third crystal form, Native-AdoHcy. The SeMet-ApoI structure was solved by the multiple anomalous dispersion method and refined at 2.55,Å resolution. The SeMet-ApoII and Native-AdoHcy structures were solved by molecular replacement and refined at 1.80 and 2.60,Å, respectively. TTHA1280 formed a homodimer in the crystals and in solution. Each subunit folds into a three-domain structure composed of a small N-terminal PUA domain, a central ,/,-domain and a C-terminal Rossmann-fold-like MTase domain. The three domains form an overall clamp-like shape, with the putative active site facing a deep cleft. The architecture of the active site is consistent with specific recognition of uridine and catalysis of methyl transfer to the 5-carbon position. The cleft is suitable in size and charge distribution for binding single-stranded RNA. [source] The size of the alpha-effects in methyl transfers correlate with Koopmans' theorem ionization potentialsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2005K. R. Fountain Abstract The size of the alpha-effects in methyl transfers to the alpha-nucleophile's peroxide anion and two N -methylbenzohydroxamate anions correlate strongly with the Koopmans' theorem ionization potentials of the leaving groups. This correlation supports the Shaik and Pross valence bond configuration mixing theory for the SN2 reaction. The Koopmans' theorem ionization potentials of the alpha-nucleophiles relate to the slopes of the regression plots inversely, indicating that the size of the alpha-effect depends on a balance between the ability of the alpha-nucleophile and the leaving group to donate single electron character to the methyl group. Copyright © 2005 John Wiley & Sons, Ltd. [source] Green Tea Polyphenols and Cancer Chemoprevention: Multiple Mechanisms and Endpoints for Phase II TrialsNUTRITION REVIEWS, Issue 5 2004M.P.H., Susan B. Moyers Ph.D. Among the numerous polyphenols isolated from green tea, the catechin EGCG predominates and is the target of anticancer research. But studies suggest that EGCG and other catechins are poorly absorbed and undergo substantial biotransformation to species that include glucuronides, sulfates, and methylated compounds. Numerous studies relate the antioxidant properties of the catechins with anticancer effects, but recent research proposes other mechanisms of action, including those involving methyl transfers that are subject to allelic variability in the enzyme catechol O-methyl transferase. However, preclinical research is promising and EGCG appears to be ready for further study in phase II and III trials. [source] | ||||||||||