Methyltransferase
Encyclopedia
Transferase
In biochemistry, a transferase is an enzyme that catalyzes the transfer of a functional group from one molecule to another . For example, an enzyme that catalyzed this reaction would be a transferase:In this example, A would be the donor, and B would be the acceptor...
enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that transfers a methyl group from a donor to an acceptor.
Methylation often occurs on nucleic bases in DNA or amino acids in protein structures. Methytransferases use a reactive methyl group bound to sulfur in S-adenosyl methionine
S-Adenosyl methionine
S-Adenosyl methionine is a common cosubstrate involved in methyl group transfers. SAM was first discovered in Italy by G. L. Cantoni in 1952. It is made from adenosine triphosphate and methionine by methionine adenosyltransferase . Transmethylation, transsulfuration, and aminopropylation are the...
(SAM) as the methyl donor.
DNA methylation
DNA methylation
DNA methylation is a biochemical process that is important for normal development in higher organisms. It involves the addition of a methyl group to the 5 position of the cytosine pyrimidine ring or the number 6 nitrogen of the adenine purine ring...
is often utilized to silence and regulate genes without changing the original DNA sequence, an example of epigenetic modification. This methylation occurs on cytosine residues. DNA methylation
DNA methylation
DNA methylation is a biochemical process that is important for normal development in higher organisms. It involves the addition of a methyl group to the 5 position of the cytosine pyrimidine ring or the number 6 nitrogen of the adenine purine ring...
may be necessary for normal growth from embryonic stages in mammals. When mutant embryonic stem cells lacking the murine DNA methyltransferase gene were introduced to a germline of mice, they caused a recessive lethal phenotype. Methylation may also be linked to cancer development, as methylation of tumor suppressor genes promotes tumorgenesis and metastasis
Metastasis
Metastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...
.
Site-specific methyltransferases have the same DNA target sequences as certain restriction enzymes. Methylation can also serve to protect DNA from enzymatic cleavage, since restriction enzymes are unable to bind and recognize externally modified sequences. This is especially useful in bacterial restriction modification system
Restriction modification system
The restriction modification system is used by bacteria, and perhaps other prokaryotic organisms to protect themselves from foreign DNA, such as the one borne by bacteriophages. This phenomenon was first noticed in the 1950s. Certain bacteria strains were found to inhibit the growth of viruses...
s that use restriction enzymes to cleave foreign DNA while keeping their own DNA protected by methylation.
Methylation of amino acids in the formation of proteins leads to more diversity of possible amino acids and, therefore, more diversity of function. The methylation reaction occurs on nitrogen atoms either on the N terminus or on the side-chain position of the protein and are usually irreversible.
Examples include:
- DNA methyltransferaseDNA methyltransferaseIn biochemistry, the DNA methyltransferase family of enzymescatalyze the transfer of a methyl group to DNA. DNA methylation serves a wide variety of biological functions...
- Histone methyltransferaseHistone methyltransferaseHistone methyltransferases are enzymes, histone-lysine N-methyltransferase and histone-arginine N-methyltransferase, that catalyze the transfer of one to three methyl groups from the cofactor S-Adenosyl methionine to lysine and arginine residues of histone proteins...
- 5-Methyltetrahydrofolate-homocysteine methyltransferase5-methyltetrahydrofolate-homocysteine methyltransferaseMethionine synthase also known as MS, MeSe, MetH is an enzyme that in humans is encoded by the MTR gene . This enzyme is responsible for the regeneration of methionine from homocysteine...
- O-methyltransferaseO-methyltransferaseAn O-methylated flavonoid is a type of methyltransferase enzyme transferring a methyl group on a molecule.Examples are :* Acetylserotonin O-methyltransferase* Apigenin 4'-O-methyltransferase* Caffeate O-methyltransferase...