Acetylation
From Wikipedia, the free encyclopedia
Acetylation (or in IUPAC nomenclature ethanoylation) describes a reaction that introduces an acetyl functional group into an organic compound. Deacetylation is the removal of the acetyl group.
Moreover, it is that process of introducing an acetyl group into a compound, specifically, the substitution of an acetyl group for an active hydrogen atom. A reaction involving the replacement of the hydrogen atom of an hydroxyl group with an acetyl group (CH3 CO) yields a specific ester, the acetate. Acetic anhydride is commonly used as an acetylating agent reacting with free hydroxyl groups.
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[edit] Acetylation of proteins
In biology, i.e. in living cells, acetylation occurs as a post-translational modification of proteins, for example, histones and tubulins.
[edit] Histone Acetylation and Deacetylation
Histones are acetylated and deacetylated on lysine residues in the N-terminal tail as part of gene regulation. Typically, these reactions are catalyzed by enzymes with "histone acetyltransferase" (HAt) or "histone deacetylase" (HDAc) activity. The source of the acetyl group in histone acetylation is Acetyl-Coenzyme A, and in histone deacetylation the acetyl group is transferred to Coenzyme A.
Acetylated histones and nucleosomes represent a type of epigenetic tag within chromatin. Acetylation brings in a negative charge and neutralizes the interaction of the N termini of histones with the phosphate groups of DNA. As a consequence, the condensed chromatin is transformed into a transiently relaxed structure which allows genes to be transcribed. Acetylated chromatin is thought to be more "relaxed" and is called euchromatin. Methylated chromatin is more condensed (tightly packed), and referred to as heterochromatin.
[edit] Tubulin Acetylation and Deacetylation
Tubulin Acetylation and Deacetylation system is well worked out in Chlamydomonas. A Tubulin acetyltransferase located in the axoneme acetylates a specific lysine residue in the α-tubulin subunit in assembled microtubule. Once dissembled, this acetylation can be removed by another specific deacetylase which is cytosolic. Thus the axonemal microtubules (long half life) carry this signature acetylation absent from cytosolic microtubules (short half life).
