SWI/SNF
Snf2 ATPase bound to a nucleosome | |||||||||
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In
The human analogs of SWI/SNF are "BRG1- or BRM-associated factors", or BAF (SWI/SNF-A) and "Polybromo-associated BAF", which is also known as PBAF (SWI/SNF-B).[6] There are also Drosophila analogs of SWI/SNF, known as "Brahma Associated Protein", or BAP and "Polybromo-associated BAP", also known as PBAP.[7]
Mechanism of action
It has been found that the SWI/SNF complex (in yeast) is capable of altering the position of
Role as a tumor suppressor
The mammalian SWI/SNF (mSWI/SNF) complex functions as a tumor suppressor in many human malignant cancers.
Role as a cancer dependency
The function of the mammalian SWI/SNF complex is highly tissue-specific,
Structure of the SWI/SNF complex
Electron microscopy studies of SWI/SNF and RSC (SWI/SNF-B) reveal large, lobed 1.1-1.3 MDa structures.[41][42][43][44] These structures resemble RecA and cover both sides of a conserved section of the ATPase domain. The domain also contains a separate domain, HSA, that is capable of binding actin, and resides on the N-terminus.[5] The bromo domain present is responsible for recognizing and binding lysines that have been acetylated.[7] No atomic-resolution structures of the entire SWI/SNF complex have been obtained to date, due to the protein complex being highly dynamic and composed of many subunits. However, domains and several individual subunits from yeast and mammals have been described. In particular, the cryo-EM structure of the ATPase Snf2 in complex with a nucleosome shows that nucleosomal DNA is locally deformed at the site of binding.[45] A model of the mammalian ATPase SMARCA4 shows similar features,[25] based on the high degree of sequence homology with yeast Snf2. The interface between two subunits, BAF155 (SMARCC1) and BAF47 (SMARCB1) was also resolved, providing important insights into the mechanisms of the SWI/SNF complex assembly pathway.[46]
SWIB/MDM2 protein domain
The protein domain, SWIB/MDM2, short for SWI/SNF complex B/MDM2 is an important domain. This protein domain has been found in both SWI/SNF complex B and in the negative regulator of the p53 tumor suppressor MDM2. It has been shown that MDM2 is homologous to the SWIB complex.[47]
Function
The primary function of the SWIB protein domain is to aid
Protein interaction
The various protein subunits that make up the SWI/SNF complex interact with each other in different configurations to form three distinct types of SWI/SNF complex: canonical BAF (cBAF), polybromo-associated BAF (pBAF) and non-canonical BAF (ncBAF). Specifically, cBAF is currently thought to regulate gene enhancers, while pBAF and ncBAF function at regions proximal to gene promoters.[49] In addition to their many interactions within the family of SWI/SNF related proteins, some subunits such as SNF5 and BAF155 are capable of interacting with transcription factors, such as c-MYC and the FOS and JUN family proteins of the AP-1 complex.[50][51]
Structure
This protein domain is known to contain one short alpha helix.
Family members
Below is a list of yeast SWI/SNF family members with human and Drosophila
Yeast | Human | Drosophila | Function |
---|---|---|---|
SWI1 | ARID1A, ARID1B | OSA | Contains LXXLL nuclear receptor binding motifs |
SWI2/SNF2 | SMARCA2, SMARCA4 | BRM | ATP dependent chromatin remodeling |
SWI3 | SMARCC1, SMARCC2 | Moira/BAP155 | Similar sequence; function unknown |
SWP73/SNF12 | SMARCD1, SMARCD2, SMARCD3 | BAP60 | Similar sequence; function unknown |
SWP61/ARP7 | ACTL6A, ACTL6B | Actin-like protein | |
SNF5 | SMARCB1 | SNR1 | ATP dependent chromatin remodeling |
History
The SWI/SNF complex was first discovered in the yeast, Saccharomyces cerevisiae. It was named after initially screening for mutations that would affect the pathways for both yeast mating types switching (SWI) and sucrose non-fermenting (SNF).[48][7]
See also
- Mdm2
- Chromatin Structure Remodeling (RSC) Complex
- Transcription coregulator
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