A bromodomain is an approximately 110 amino acid

protein domain In molecular biology, a protein domain is a region of a protein's Peptide, polypeptide chain that is self-stabilizing and that Protein folding, folds independently from the rest. Each domain forms a compact folded Protein tertiary structure, thre ...

that recognizes

acetylated : In chemistry, acetylation is an organic esterification reaction with acetic acid. It introduces an acetyl group into a chemical compound. Such compounds are termed ''acetate esters'' or simply ''acetates''. Deacetylation is the opposite reacti ...

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. Lysine contains an α-amino group (which is in the protonated form when the lysine is dissolved in water at physiological pH), an α-carboxylic acid group ( ...

residues, such as those on the ''N''-terminal tails of

histone In biology, histones are highly basic proteins abundant in lysine and arginine residues that are found in eukaryotic cell nuclei and in most Archaeal phyla. They act as spools around which DNA winds to create structural units called nucleosomes ...

s. Bromodomains, as the "readers" of lysine acetylation, are responsible in transducing the signal carried by acetylated lysine residues and translating it into various normal or abnormal phenotypes. Their affinity is higher for regions where multiple acetylation sites exist in proximity. This recognition is often a prerequisite for protein-histone association and

chromatin Chromatin is a complex of DNA and protein found in eukaryote, eukaryotic cells. The primary function is to package long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important r ...

remodeling. The domain itself adopts an all-α protein fold, a bundle of four

alpha helices An alpha helix (or α-helix) is a sequence of amino acids in a protein that are twisted into a coil (a helix). The alpha helix is the most common structural arrangement in the secondary structure of proteins. It is also the most extreme type of l ...

each separated by loop regions of variable lengths that form a hydrophobic pocket that recognizes the acetyl lysine.

Discovery

The bromodomain was identified as a novel

structural motif In a chain-like biological molecule, such as a protein or nucleic acid, a structural motif is a common three-dimensional structure that appears in a variety of different, evolutionarily unrelated molecules. A structural motif does not have t ...

by John W. Tamkun and colleagues studying the

Drosophila ''Drosophila'' (), from Ancient Greek δρόσος (''drósos''), meaning "dew", and φίλος (''phílos''), meaning "loving", is a genus of fly, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or p ...

gene ''

Brahma Brahma (, ) is a Hindu god, referred to as "the Creator" within the Trimurti, the triple deity, trinity of Para Brahman, supreme divinity that includes Vishnu and Shiva.Jan Gonda (1969)The Hindu Trinity, Anthropos, Bd 63/64, H 1/2, pp. 212– ...

''/''brm'', and showed sequence similarity to genes involved in transcriptional activation. The name "bromodomain" is derived from the relationship of this domain with ''Brahma'' and is unrelated to the chemical element

bromine Bromine is a chemical element; it has chemical symbol, symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between th ...

Bromodomain-containing proteins

Bromodomain-containing proteins can have a wide variety of functions, ranging from histone acetyltransferase activity and chromatin remodeling to transcriptional mediation and co-activation. Of the 43 known in 2015, 11 had two bromodomains, and one protein had 6 bromodomains. Preparation, biochemical analysis, and structure determination of the bromodomain containing proteins have been described in detail.

Bromo- and Extra-Terminal domain (BET) family

A well-known example of a bromodomain family is the BET (Bromodomain and extraterminal domain) family. Members of this family include

BRD2 Bromodomain-containing protein 2 is a protein that in humans is encoded by the ''BRD2'' gene. BRD2 is part of the Bromodomain and Extra-Terminal motif (BET) protein family that also contains BRD3, BRD4, and BRDT in mammals Early descriptions d ...

BRD3 Bromodomain-containing protein 3 (BRD3) also known as RING3-like protein (RING3L) is a protein that in humans is encoded by the BRD3 gene. This gene was identified based on its homology to the gene encoding the RING3 ( BRD2) protein, a serine/thr ...

BRD4 Bromodomain-containing protein 4 is a protein that in humans is encoded by the ''BRD4'' gene. BRD4 is a member of the BET (bromodomain and extra terminal domain) family, which also includes BRD2, BRD3, and BRDT. BRD4, similar to other BET fam ...

and BRDT.

Other

However proteins such as

ASH1L ASH1L (also called huASH1, ASH1, ASH1L1, ASH1-like, or KMT2H) is a histone-lysine N-methyltransferase enzyme encoded by the ''ASH1L'' gene located at chromosomal band 1q22. ASH1L is the human homolog of Drosophila Ash1 (absent, small, or homeoti ...

also contain a bromodomain. Dysfunction of BRD proteins has been linked to diseases such as human squamous cell carcinoma and other forms of cancer.

Histone acetyltransferases Histone acetyltransferases (HATs) are enzymes that acetylate conserved lysine amino acids on histone proteins by transferring an acetyl group from acetyl-CoA to form ε-''N''-acetyllysine. DNA is wrapped around histones, and, by transferring an ...

, including

EP300 Histone acetyltransferase p300 also known as p300 HAT or E1A-associated protein p300 (where E1A = adenovirus early region 1A) also known as EP300 or p300 is an enzyme that, in humans, is encoded by the ''EP300'' gene. It functions as histone ace ...

and

PCAF P300/CBP-associated factor (PCAF), also known as K(lysine) acetyltransferase 2B (KAT2B), is a human gene and transcriptional coactivator associated with p53. Structure Several domains of PCAF can act independently or in unison to enable its fu ...

, have bromodomains in addition to acetyl-transferase domains. Not considered part of the BET family (yet containing a bromodomain) are

BRD7 Bromodomain-containing protein 7 is a protein that in humans is encoded by the ''BRD7'' gene. Interactions BRD7 has been shown to interact with IRF2 and HNRPUL1. Azoospermia BRD7 protein is a transcription regulator that is normally highly e ...

, and

BRD9 Bromodomain-containing protein 9 is a protein that in humans is encoded by the ''BRD9'' gene. Structure and interaction BRD9 contains a bromodomain. It is closely related to BRD7. BRD9 is present in some SWI/SNF ATPase remodeling complexes. Ro ...

Role in human disease

The role of bromodomains in translating a deregulated cell acetylome into disease phenotypes was recently unveiled by the development of small molecule bromodomain inhibitors. This breakthrough discovery highlighted bromodomain-containing proteins as key players in cancer biology, as well as inflammation and

remyelination Remyelination is the process of propagating oligodendrocyte precursor cells to form oligodendrocytes to create new myelin sheaths on demyelinated axons in the Central nervous system (CNS). This is a process naturally regulated in the body and tend ...

multiple sclerosis Multiple sclerosis (MS) is an autoimmune disease resulting in damage to myelinthe insulating covers of nerve cellsin the brain and spinal cord. As a demyelinating disease, MS disrupts the nervous system's ability to Action potential, transmit ...

. Members of the BET family have been implicated as targets in both human cancer and multiple sclerosis.

BET inhibitors BET inhibitors are a class of drugs that reversibly bind the bromodomains of Bromodomain and Extra-Terminal motif (BET) proteins BRD2, BRD3, BRD4, and BRDT, and prevent protein-protein interaction between BET proteins and acetylated histones an ...

have shown therapeutic effects in multiple preclinical models of cancer and are currently in clinical trials in the United States. Their application in multiple sclerosis is still in the preclinical stage. Small molecule inhibitors of non-BET bromodomain proteins

and

have also been developed.

References