Demethylase

Demethylases are enzymes that remove methyl (CH3-) groups from nucleic acids, proteins (in particular histones), and other molecules. Demethylase enzymes are important in epigenetic modification mechanisms. The demethylase proteins alter transcriptional regulation of the genome by controlling the methylation levels that occur on DNA and histones and, in turn, regulate the chromatin state at specific gene loci within organisms. Demethylases are enzymes that remove methyl (CH3-) groups from nucleic acids, proteins (in particular histones), and other molecules. Demethylase enzymes are important in epigenetic modification mechanisms. The demethylase proteins alter transcriptional regulation of the genome by controlling the methylation levels that occur on DNA and histones and, in turn, regulate the chromatin state at specific gene loci within organisms. For many years histone methylation was thought to be irreversible, due to the fact that the half-life of the histone methylation was approximately equal to the half-life of histones themselves. In 2004, Shi et al. published their discovery of the histone demethylase LSD1 (later classified as KDM1A), a nuclear amine oxidase homolog. Since then many more histone demethylases have been found. Defined by their mechanisms, two main classes of histone demethylases exist: a flavin adenine dinucleotide (FAD)-dependent amine oxidase, and an Fe(II) and α-ketoglutarate-dependent hydroxylase. Both operate by hydroxylation of a methyl group, followed by dissociation of formaldehyde. Demethylation has implications for epigenetics. Histone demethylase proteins have a variety of domains that serve different functions. These functions include binding to the histone (or sometimes the DNA on the nucleosome), recognizing the correct methylated amino acid substrate and catalyzing the reaction, and binding cofactors. Cofactors include:alpha-keto glutarate (JmjC-domain containing demethylases), CoREST (LSD), FAD, Fe (II) or NOG (N-oxalylglycine). Domains include: There are several families of histone demethylases, which act on different substrates and play different roles in cellular function. A code has been developed to indicate the substrate for a histone demethylase. The substrate is first specified by the histone subunit (H1, H2A, H2B, H3, H4) and then the one letter designation and number of the amino acid that is methylated. Lastly, the level of methylation is sometimes noted by the addition of 'me#', with the numbers being 1, 2, and 3 for monomethylated, dimethylated, and trimethylated substrates, respectively. For example, H3K9me2 is histone H3 with a dimethylated lysine in the ninth position. Another example of a demethylase is protein-glutamate methylesterase, also known as CheB protein (EC 3.1.1.61), which demethylates MCPs (methyl-accepting chemotaxis proteins) through hydrolysis of carboxylic ester bonds. The association of a chemotaxis receptor with an agonist leads to the phosphorylation of CheB. Phosphorylation of CheB protein enhances its catalytic MCP demethylating activity resulting in adaption of the cell to environmental stimuli. MCPs respond to extracellular attractants and repellents in bacteria like E. coli in chemotaxis regulation. CheB is more specifically termed a methylesterase, as it removes methyl groups from methylglutamate residues located on the MCPs through hydrolysis, producing glutamate accompanied by the release of methanol. CheB is of particular interest to researchers as it may be a therapeutic target for mitigating the spread of bacterial infections.