histone methyltransferase activity

Definition

Target type: molecularfunction

Catalysis of the reaction: S-adenosyl-L-methionine + histone = S-adenosyl-L-homocysteine + methyl-histone. Histone methylation generally occurs on either an arginine or a lysine residue. [GOC:curators]

Histone methyltransferases (HMTs) are a family of enzymes that catalyze the transfer of a methyl group from a donor molecule, typically S-adenosyl methionine (SAM), to a specific lysine or arginine residue within histone proteins. This methylation process plays a crucial role in regulating gene expression by altering the accessibility of DNA to transcription factors and other regulatory proteins.

HMTs are highly specific for both the histone target and the methylation site, and their activity is regulated by a variety of factors, including cellular signaling pathways, developmental stage, and environmental cues. The addition of a methyl group to a histone tail can have different effects on gene expression depending on the specific residue modified, the number of methyl groups added, and the context of the surrounding chromatin environment.

**Specific examples of the molecular function of histone methyltransferase activity include:**

* **Activation of gene expression:** Methylation of lysine 4 on histone H3 (H3K4me) is generally associated with active transcription, as it attracts proteins that promote transcription initiation and elongation.
* **Repression of gene expression:** Methylation of lysine 9 on histone H3 (H3K9me) is often linked to gene silencing, as it recruits proteins that condense chromatin and hinder transcription factor access.
* **Regulation of DNA replication and repair:** Methylation of histone H3 lysine 79 (H3K79me) plays a role in DNA replication and repair processes.
* **Chromatin remodeling:** Methylation of histone H3 lysine 27 (H3K27me) is involved in the formation of silent chromatin domains, which can be targeted for specific developmental or differentiation programs.

**Mechanism of HMT Activity:**

HMTs typically consist of a SET domain, which is a highly conserved catalytic domain responsible for transferring the methyl group. They often interact with other proteins, such as histone chaperones or chromatin-remodeling complexes, to facilitate their access to histone substrates.

The catalytic cycle of an HMT involves the following steps:

1. Binding of the HMT to its histone substrate and SAM.
2. Transfer of a methyl group from SAM to the target lysine or arginine residue on the histone tail.
3. Release of the methylated histone and S-adenosyl homocysteine (SAH), the byproduct of the reaction.

**Dysregulation of HMT activity is associated with a variety of diseases, including cancer, developmental disorders, and neurological diseases.**'
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Proteins (17)

Compounds (63)