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Acetylation

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The medical definition of acetylation is "The substitution of an acetyl radical for an active hydrogen. A reaction involving the replacement of the hydrogen atom of an hydroxyl group with an acetyl radical (CH 3 CO) to yield a specific ester, the acetate. Acetic anhydride is commonly used as an acetylating agent reacting with free hydroxyl groups."

Acetylation Histone Acetylation and How it Works

Acetylation is a reaction, usually with acetic acid, that introduces an acetyl radical into an organic compound. It is one of the synthetic biotransformations which operate in the metabolism of drugs in which metabolites are produced that are more readily excreted than the parent drug. Dogs are exceptional amongst the domesticated species in that acetylation does not occur in their tissues. Acetylation is one of the principal metabolic pathways of the sulfonamides. As an example, Salicylic acid is acetylated and forms aspirin.

 

Protein Acetylation

N-alpha-terminal Acetylation

Acetylation of the N-terminal alpha-amine of proteins is a widespread modification in eukaryotes. Forty to fifty percent of yeast proteins and between 80 to 90% of human proteins are modified in this manner. The pattern of modification is found to be the same throughout evolution.

The modification is performed by N-alpha-acetyltransferases (NATs), a sub-family of the GNAT super family of acetyltransferases, which also includes histone acetyl transferases. The GNATs transfer the acetyl group from acetyl-coenzyme A to the amine group. The NATs have been most extensively studied in yeast. Here, three NAT complexes, NatA/B/C, have been found to perform most N-alpha-terminal acetylations. They have sequence specificity for their substrates, and it is believed that they are associated with the ribosome.

Acetylation in the Human BodyAcetylation in the Human Body

In humans, the human NatA and NatB complexes have been identified and characterized. Subunits of the human NatA complex have been coupled to cancer-related processes such as hypoxia-response and the beta-catenin pathway. It has been found to be over-expressed in papillary thyroid carcinoma and neuroblastoma.

The human NatB complex has been coupled to cell cycle. The hNat3 subunit of the hNatB complex has been found over-expressed in some forms of cancer. Despite being such a conserved and widespread modification, little is known about the biological role of N-alpha-terminal acetylation. Proteins such as actin and tropomyosin have been found to be dependent of NatB acetylation to form proper actin filaments.

For unknown reasons 20% of Asians have an isozyme that results in slower N-acetylation of drugs, while 50% of Whites and African-Americans do.

 

Histone Acetylation occurs on the surface of the nucleosome core as part of gene regulation when the histones are acetylated on lysine residues. Acetylation brings in a negative charge that acts to neutralize the positive charge on the histones, and decreases the interaction of the N termini of histones with the negatively charged phosphate groups of DNA.

Gene Control through histone acetylation and deacetylation