Pyrrolysine is an α-amino acid that is used in the biosynthesis of proteins in some methanogenic archaea and bacteria; it is not present in humans. It contains an α-amino group, a carboxylic acid group. Its pyrroline side-chain is similar to that of lysine in being basic and positively charged at neutral pH.
In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These terms are commonly used in chemistry, biochemistry, soil science, and the biological sciences.
In biochemistry, the DNA methyltransferase family of enzymes catalyze the transfer of a methyl group to DNA. DNA methylation serves a wide variety of biological functions. All the known DNA methyltransferases use S-adenosyl methionine (SAM) as the methyl donor.
Methyltransferases are a large group of enzymes that all methylate their substrates but can be split into several subclasses based on their structural features. The most common class of methyltransferases is class I, all of which contain a Rossmann fold for binding S-Adenosyl methionine (SAM). Class II methyltransferases contain a SET domain, which are exemplified by SET domain histone methyltransferases, and class III methyltransferases, which are membrane associated. Methyltransferases can also be grouped as different types utilizing different substrates in methyl transfer reactions. These types include protein methyltransferases, DNA/RNA methyltransferases, natural product methyltransferases, and non-SAM dependent methyltransferases. SAM is the classical methyl donor for methyltransferases, however, examples of other methyl donors are seen in nature. The general mechanism for methyl transfer is a SN2-like nucleophilic attack where the methionine sulfur serves as the leaving group and the methyl group attached to it acts as the electrophile that transfers the methyl group to the enzyme substrate. SAM is converted to S-Adenosyl homocysteine (SAH) during this process. The breaking of the SAM-methyl bond and the formation of the substrate-methyl bond happen nearly simultaneously. These enzymatic reactions are found in many pathways and are implicated in genetic diseases, cancer, and metabolic diseases. Another type of methyl transfer is the radical S-Adenosyl methionine (SAM) which is the methylation of unactivated carbon atoms in primary metabolites, proteins, lipids, and RNA.
In enzymology, a protein-glutamate O-methyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a lysine-tRNAPyl ligase is an enzyme that catalyzes the chemical reaction
Demethylmenaquinone methyltransferase is an enzyme with systematic name S-adenosyl-L-methionine:demethylmenaquinone methyltransferase. This enzyme catalyses the following chemical reaction
5-methyltetrahydrosarcinapterin:corrinoid/iron-sulfur protein Co-methyltransferase is an enzyme with systematic name 5-methyltetrahydrosarcinapterin:corrinoid/iron-sulfur protein methyltransferase. This enzyme catalyses the following chemical reaction:
(Methyl-Co methanol-specific corrinoid protein):coenzyme M methyltransferase is an enzyme with systematic name methylated methanol-specific corrinoid protein:coenzyme M methyltransferase. This enzyme catalyses the following chemical reaction
(Methyl-Co methylamine-specific corrinoid protein):coenzyme M methyltransferase is an enzyme with systematic name methylated monomethylamine-specific corrinoid protein:coenzyme M methyltransferase. This enzyme catalyses the following chemical reaction
Methylamine-corrinoid protein Co-methyltransferase is an enzyme with systematic name monomethylamine:5-hydroxybenzimidazolylcobamide Co-methyltransferase. This enzyme catalyses the following chemical reaction
Dimethylamine-corrinoid protein Co-methyltransferase is an enzyme with systematic name dimethylamine:5-hydroxybenzimidazolylcobamide Co-methyltransferase. This enzyme catalyses the following chemical reaction
Methylated-thiol-coenzyme M methyltransferase is an enzyme with systematic name methylated-thiol:coenzyme M methyltransferase. This enzyme catalyses the following chemical reaction:
Tetramethylammonium-corrinoid protein Co-methyltransferase is an enzyme with systematic name tetramethylammonium:5-hydroxybenzimidazolylcobamide Co-methyltransferase. This enzyme catalyses the following chemical reaction
(Methyl-Co tetramethylammonium-specific corrinoid protein):coenzyme M methyltransferase is an enzyme with systematic name methylated tetramethylammonium-specific corrinoid protein:coenzyme M methyltransferase. This enzyme catalyses the following chemical reaction
5-methyltetrahydrofolate:corrinoid/iron-sulfur protein Co-methyltransferase is an enzyme with systematic name 5-methyltetrahydrofolate:corrinoid/iron-sulfur protein methyltransferase. This enzyme catalyses the following chemical reaction
Rowena Green Matthews, born in 1938, is the G. Robert Greenberg Distinguished University professor emeritus at the University of Michigan, Ann Arbor. Her research focuses on the role of organic cofactors as partners of enzymes catalyzing difficult biochemical reactions, especially folic acid and cobalamin. Among other honors, she was elected to the National Academy of Sciences in 2002 and the Institute of Medicine in 2004.
Protein methylation is a type of post-translational modification featuring the addition of methyl groups to proteins. It can occur on the nitrogen-containing side-chains of arginine and lysine, but also at the amino- and carboxy-termini of a number of different proteins. In biology, methyltransferases catalyze the methylation process, activated primarily by S-adenosylmethionine. Protein methylation has been most studied in histones, where the transfer of methyl groups from S-adenosyl methionine is catalyzed by histone methyltransferases. Histones that are methylated on certain residues can act epigenetically to repress or activate gene expression.
Cobamide is a naturally occurring chemical compound containing cobalt in the corrinoid family of macrocyclic complexes. Cobamide works as a coenzyme with some enzymes in bacteria. The cobalt atom may have a transferable methyl group attached. It is used for example in 5-methyltetrahydrosarcinapterin:corrinoid/iron-sulfur protein Co-methyltransferase.
Coenzyme Q5, methyltransferase, more commonly known as COQ5, is an enzyme involved in the electron transport chain. COQ5 is located within the mitochondrial matrix and is a part of the biosynthesis of ubiquinone.
