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Accounts of Chemical Research Apr 2012Methylation is an essential and ubiquitous reaction that plays an important role in a wide range of biological processes. Most biological methylations use... (Review)
Review
Methylation is an essential and ubiquitous reaction that plays an important role in a wide range of biological processes. Most biological methylations use S-adenosylmethionine (SAM) as the methyl donor and proceed via an S(N)2 displacement mechanism. However, researchers have discovered an increasing number of methylations that involve radical chemistry. The enzymes known to catalyze these reactions all belong to the radical SAM superfamily. This family of enzymes utilizes a specialized [4Fe-4S] cluster for reductive cleavage of SAM to yield a highly reactive 5'-deoxyadenosyl (dAdo) radical. Radical chemistry is then imposed on a variety of organic substrates, leading to a diverse array of transformations. Until recently, researchers had not fully understood how these enzymes employ radical chemistry to mediate a methyl transfer reaction. Sequence analyses reveal that the currently identified radical SAM methyltransferases (RSMTs) can be grouped into three classes, which appear distinct in protein architecture and mechanism. Class A RSMTs mainly include the rRNA methyltransferases RlmN and Cfr from various origins. As exemplified by Escherichia coli RlmN, these proteins have a single canonical radical SAM core domain that includes an (βα)(6) partial barrel most similar to that of pyruvate formate lyase-activase. The exciting recent studies on RlmN and Cfr are beginning to provide insights into the intriguing chemistry of class A RSMTs. These enzymes utilize a methylene radical generated on a unique methylated cysteine residue. However, based on the variety of substrates used by the other classes of RSMTs, alternative mechanisms are likely to be discovered. Class B RSMTs contain a proposed N-terminal cobalamin binding domain in addition to a radical SAM domain at the C-terminus. This class of proteins methylates diverse substrates at inert sp(3) carbons, aromatic heterocycles, and phosphinates, possibly involving a cobalamin-mediated methyl transfer process. Class C RSMTs share significant sequence similarity with coproporphyrinogen III oxidase HemN. Despite methylating similar substrates (aromatic heterocycles), class C RSMTs likely employ a mechanism distinct from that of class A because two conserved cysteines that are required for class A are typically not found in class C RSMTs. Class A and class B enzymes probably share the use of two molecules of SAM: one to generate a dAdo radical and one to provide the methyl group to the substrate. In class A, a cysteine would act as a conduit of the methyl group whereas in class B cobalamin may serve this purpose. Currently no clues are available regarding the mechanism of class C RSMTs, but the sequence similarities between its members and HemN and the observation that HemN binds two SAM molecules suggest that class C enzymes could use two SAM molecules for catalysis. The diverse strategies for using two SAM molecules reflect the rich chemistry of radical-mediated methylation reactions and the remarkable versatility of the radical SAM superfamily.
Topics: Free Radicals; Methylation; Methyltransferases; S-Adenosylmethionine; Vitamin B 12
PubMed: 22097883
DOI: 10.1021/ar200202c -
Structure (London, England : 1993) Jan 2022Methyl-TROSY spectroscopy has extended the reach of solution-state NMR to supra-molecular machineries over 100 kDa in size. Methyl groups are ideal probes for studying...
Methyl-TROSY spectroscopy has extended the reach of solution-state NMR to supra-molecular machineries over 100 kDa in size. Methyl groups are ideal probes for studying structure, dynamics, and protein-protein interactions in quasi-physiological conditions with atomic resolution. Successful implementation of the methodology requires accurate methyl chemical shift assignment, and the task still poses a significant challenge in the field. In this work, we outline the current state of technology for methyl labeling, data collection, data analysis, and nuclear Overhauser effect (NOE)-based automated methyl assignment approaches. We present MAGIC-Act and MAGIC-View, two Python extensions developed as part of the popular NMRFAM-Sparky package, and MAGIC-Net a standalone structure-based network analysis program. MAGIC-Act conducts statistically driven amino acid typing, Leu/Val pairing guided by 3D HMBC-HMQC, and NOESY cross-peak symmetry checking. MAGIC-Net provides model-based NOE statistics to aid in selection of a methyl labeling scheme. The programs provide a versatile, semi-automated framework for rapid methyl assignment.
Topics: Algorithms; Amino Acids; Humans; Methylation; Models, Molecular; Nuclear Magnetic Resonance, Biomolecular; Protein Binding; Proteins
PubMed: 34914892
DOI: 10.1016/j.str.2021.11.009 -
Methods in Enzymology 2019Since protein activity is often regulated by posttranslational modifications, the qualitative and quantitative analysis of modification sites is critical for...
Since protein activity is often regulated by posttranslational modifications, the qualitative and quantitative analysis of modification sites is critical for understanding the regulation of biological pathways that control cell function and phenotype. Methylation constitutes one of the many types of posttranslational modifications that target lysine residues. Although lysine methylation is perhaps most commonly associated with histone proteins and the epigenetic regulation of processes involving chromatin, methylation has also been observed as an important regulatory modification on other proteins, which has spurred the development of methods to profile lysine methylation sites more globally. As with many posttranslational modifications, tandem mass spectrometry represents an ideal platform for the high-throughput analysis of lysine methylation due to its high sensitivity and resolving power. The following protocol outlines a general method to assay lysine methylation across the proteome using SILAC and quantitative proteomics. First, cells are labeled by SILAC to allow for relative quantitation across different experimental conditions, such as cells with or without ectopic expression of a methyltransferase. Next, cells are lysed and proteins are digested into peptides. Methylated peptides are then enriched by immunoprecipitation with pan-specific antibodies against methylated lysine. Finally, the enriched peptides are analyzed by LC-MS/MS to identify methylated peptides and their modification sites and to compare the relative abundance of methylation events between different conditions. This approach should yield detection of a couple hundred lysine methylation sites, and those showing differential abundance may then be prioritized for further study.
Topics: Animals; Chromatography, Liquid; Humans; Lysine; Methylation; Protein Processing, Post-Translational; Proteins; Tandem Mass Spectrometry
PubMed: 31606088
DOI: 10.1016/bs.mie.2019.07.036 -
Journal of Translational Medicine Feb 2021Neurotrophic tropomyosin receptor kinases (NTRKs) are a gene family function as oncogene or tumor suppressor gene in distinct cancers. We aimed to investigate the...
BACKGROUND
Neurotrophic tropomyosin receptor kinases (NTRKs) are a gene family function as oncogene or tumor suppressor gene in distinct cancers. We aimed to investigate the methylation and expression profiles and prognostic value of NTRKs gene in colorectal cancer (CRC).
METHODS
An analysis of DNA methylation and expression profiles in CRC patients was performed to explore the critical methylations within NTRKs genes. The methylation marker was validated in a retrospectively collected cohort of 229 CRC patients and tested in other tumor types from TCGA. DNA methylation status was determined by quantitative methylation-specific PCR (QMSP).
RESULTS
The profiles in six CRC cohorts showed that NTRKs gene promoter was more frequently methylated in CRC compared to normal mucosa, which was associated with suppressed gene expression. We identified a specific methylated region within NTRK3 promoter targeted by cg27034819 and cg11525479 that best predicted survival outcome in CRC. NTRK3 promoter methylation showed independently predictive value for survival outcome in the validation cohort (P = 0.004, HR 2.688, 95% CI [1.355, 5.333]). Based on this, a nomogram predicting survival outcome was developed with a C-index of 0.705. Furthermore, the addition of NTRK3 promoter methylation improved the performance of currently-used prognostic model (AIC: 516.49 vs 513.91; LR: 39.06 vs 43.64, P = 0.032). Finally, NTRK3 promoter methylation also predicted survival in other tumors, including pancreatic cancer, glioblastoma and stomach adenocarcinoma.
CONCLUSIONS
This study highlights the essential value of NTRK3 methylation in prognostic evaluation and the potential to improve current prognostic models in CRC and other tumors.
Topics: Biomarkers, Tumor; Colorectal Neoplasms; DNA Methylation; Humans; Prognosis; Receptor, trkC; Retrospective Studies; Tropomyosin
PubMed: 33593392
DOI: 10.1186/s12967-021-02740-6 -
The International Journal of... 2009Genes constitute only a small proportion of the mammalian genome, the majority of which is composed of non-genic repetitive elements including interspersed repeats and... (Review)
Review
Genes constitute only a small proportion of the mammalian genome, the majority of which is composed of non-genic repetitive elements including interspersed repeats and satellites. A unique feature of the mammalian genome is that there are numerous tissue-dependent, differentially methylated regions (T-DMRs) in the non-repetitive sequences, which include genes and their regulatory elements. The epigenetic status of T-DMRs varies from that of repetitive elements and constitutes the DNA methylation profile genome-wide. Since the DNA methylation profile is specific to each cell and tissue type, much like a fingerprint, it can be used as a means of identification. The formation of DNA methylation profiles is the basis for cell differentiation and development in mammals. The epigenetic status of each T-DMR is regulated by the interplay between DNA methyltransferases, histone modification enzymes, histone subtypes, non-histone nuclear proteins and non-coding RNAs. In this review, we will discuss how these epigenetic factors cooperate to establish cell- and tissue-specific DNA methylation profiles.
Topics: Amino Acid Sequence; Animals; Chromatin Assembly and Disassembly; DNA Methylation; Epigenesis, Genetic; Histones; Methylation; Models, Biological; Molecular Sequence Data; Stem Cells
PubMed: 19412882
DOI: 10.1387/ijdb.082741ki -
Journal of Dental Research Nov 2020The packaging of DNA around nucleosomes exerts dynamic control over eukaryotic gene expression either by granting access to the transcriptional machinery in an open...
The packaging of DNA around nucleosomes exerts dynamic control over eukaryotic gene expression either by granting access to the transcriptional machinery in an open chromatin state or by silencing transcription via chromatin compaction. Histone methylation modification affects chromatin through the addition of methyl groups to lysine or arginine residues of histones H3 and H4 by means of histone methyl transferases or histone demethylases. Changes in histone methylation state modulate periodontal gene expression and have profound effects on periodontal development, health, and therapy. At the onset of periodontal development, progenitor cell populations such as dental follicle cells are characterized by an open H3K4me3 chromatin mark on RUNX2, MSX2, and DLX5 gene promoters. During further development, periodontal progenitor differentiation undergoes a global switch from the H3K4me3 active methyl mark to the H3K27me3 repressive mark. When compared with dental pulp cells, periodontal neural crest lineage differentiation is characterized by repressive H3K9me3 and H3K27me3 marks on typical dentinogenesis-related genes. Inflammatory conditions as they occur during periodontal disease result in unique histone methylation signatures in affected cell populations, including repressive H3K9me3 and H3K27me3 histone marks on extracellular matrix gene promoters and active H3K4me3 marks on interleukin, defensin, and chemokine gene promoters, facilitating a rapid inflammatory response to microbial pathogens. The inflammation-induced repression of chromatin on extracellular matrix gene promoters presents a therapeutic opportunity for the application of histone methylation inhibitors capable of inhibiting suppressive trimethylation marks. Furthermore, inhibition of chromatin coregulators through interference with key inflammatory mediators such as NF-kB by means of methyltransferase inhibitors provides another avenue to halt the exacerbation of the inflammatory response in periodontal tissues. In conclusion, histone methylation dynamics play an intricate role in the fine-tuning of chromatin states during periodontal development and harbor yet-to-be-realized potential for the treatment of periodontal disease.
Topics: DNA Methylation; Epigenesis, Genetic; Histones; Homeostasis; Lysine; Methylation; Protein Processing, Post-Translational
PubMed: 32762486
DOI: 10.1177/0022034520932491 -
Research in Microbiology 2020Mercury methylation converts inorganic mercury into the toxic methylmercury, and the consequences of this transformation are worrisome for human health and the...
Mercury methylation converts inorganic mercury into the toxic methylmercury, and the consequences of this transformation are worrisome for human health and the environment. This process is performed by anaerobic microorganisms, such as several strains related to Pseudodesulfovibrio and Desulfovibrio genera. In order to provide new insights into the molecular mechanisms of mercury methylation, we performed a comparative genomic analysis on mercury methylators and non-methylators from (Pseudo)Desulfovibrio strains. Our results showed that (Pseudo)Desulfovibrio species are phylogenetically and metabolically distant and consequently, these genera should be divided into various genera. Strains able to perform methylation are affiliated with one branch of the phylogenetic tree, but, except for hgcA and hgcB genes, no other specific genetic markers were found among methylating strains. hgcA and hgcB genes can be found adjacent or separated, but proximity between those genes does not promote higher mercury methylation. In addition, close examination of the non-methylator Pseudodesulfovibrio piezophilus C1TLV30 strain, showed a syntenic structure that suggests a recombination event and may have led to hgcB depletion. The genomic analyses identify also arsR gene coding for a putative regulator upstream hgcA. Both genes are cotranscribed suggesting a role of ArsR in hgcA expression and probably a role in mercury methylation.
Topics: Bacterial Proteins; Desulfovibrio; Desulfovibrionaceae; Gene Expression Regulation, Bacterial; Genome, Bacterial; Mercury; Methylation; Phylogeny
PubMed: 31655199
DOI: 10.1016/j.resmic.2019.10.003 -
ACS Chemical Biology Jul 2020The methylation of amide nitrogen atoms can improve the stability, oral availability, and cell permeability of peptide therapeutics. Chemical -methylation of peptides is...
The methylation of amide nitrogen atoms can improve the stability, oral availability, and cell permeability of peptide therapeutics. Chemical -methylation of peptides is challenging. Omphalotin A is a ribosomally synthesized, macrocylic dodecapeptide with nine backbone -methylations. The fungal natural product is derived from the precursor protein, OphMA, harboring both the core peptide and a SAM-dependent peptide α--methyltransferase domain. OphMA forms a homodimer and its α--methyltransferase domain installs the methyl groups on the hydrophobic core dodecapeptide and some additional C-terminal residues of the protomers. These post-translational backbone -methylations occur in a processive manner from the N- to the C-terminus of the peptide substrate. We demonstrate that OphMA can methylate polar, aromatic, and charged residues when these are introduced into the core peptide. Some of these amino acids alter the efficiency and pattern of methylation. Proline, depending on its sequence context, can act as a tunable stop signal. Crystal structures of OphMA variants have allowed rationalization of these observations. Our results hint at the potential to control this fungal α--methyltransferase for biotechnological applications.
Topics: Agaricales; Amino Acid Sequence; Fungal Proteins; Methylation; Methyltransferases; Mutation; Peptides, Cyclic; Protein Domains; Protein Precursors; Protein Processing, Post-Translational; Substrate Specificity
PubMed: 32491837
DOI: 10.1021/acschembio.0c00237 -
The EMBO Journal Sep 1998The three-way connection between DNA methylation, gene activity and chromatin structure has been known for almost two decades. Nevertheless, the molecular link between... (Review)
Review
The three-way connection between DNA methylation, gene activity and chromatin structure has been known for almost two decades. Nevertheless, the molecular link between methyl groups on the DNA and the positioning of nucleosomes to form an inactive chromatin configuration was missing. This review discusses recent experimental data that may, for the first time, shed light on this molecular link. MeCP2, which is a known methylcytosine-binding protein, has been shown to possess a transcriptional repressor domain (TRD) that binds the corepressor mSin3A. This corepressor protein constitutes the core of a multiprotein complex that includes histone deacetylases (HDAC1 and HDAC2). Transfection and injection experiments with methylated constructs have revealed that the silenced state of a methylated gene, which is associated with a deacetylated nucleosomal structure, could be relieved by the deacetylase inhibitor, trichostatin A. Thus, methylation plays a pivotal role in establishing and maintaining an inactive state of a gene by rendering the chromatin structure inaccessible to the transcription machinery.
Topics: Chromatin; DNA Methylation; Gene Expression Regulation; Models, Genetic
PubMed: 9724627
DOI: 10.1093/emboj/17.17.4905 -
Epigenetics Dec 2022DNA methylation on CpGs regulates transcription in mammals, both by decreasing the binding of methylation-repelled factors and by increasing the binding of...
DNA methylation on CpGs regulates transcription in mammals, both by decreasing the binding of methylation-repelled factors and by increasing the binding of methylation-attracted factors. Among the latter, zinc finger proteins have the potential to bind methylated CpGs in a sequence-specific context. The protein ZBTB38 is unique in that it has two independent sets of zinc fingers, which recognize two different methylated consensus sequences . Here, we identify the binding sites of ZBTB38 in a human cell line, and show that they contain the two methylated consensus sequences identified . In addition, we show that the distribution of ZBTB38 sites is highly unusual: while 10% of the ZBTB38 sites are also bound by CTCF, the other 90% of sites reside in closed chromatin and are not bound by any of the other factors mapped in our model cell line. Finally, a third of ZBTB38 sites are found upstream of long and active CpG islands. Our work therefore validates ZBTB38 as a methyl-DNA binder and identifies its unique distribution in the genome.
Topics: Animals; Humans; Transcription Factors; DNA Methylation; CpG Islands; Zinc Fingers; Gene Expression Regulation; Binding Sites; Protein Binding; Mammals; Repressor Proteins
PubMed: 36000449
DOI: 10.1080/15592294.2022.2111135