BAZ2B

BAZ2B is a chromatin-associated regulatory subunit of ISWI-type ATP-dependent chromatin remodeling complexes (BRF1 and BRF5) that reads histone acetylation marks and modulates transcription at gene promoters (PMID:38000389). Its bromodomain recognizes acetylated lysine—notably H3K14ac—through a shallow, canonical pocket featuring a conserved Tyr1901 residue critical for ligand coordination, while its TAM domain binds double-stranded DNA without methylation preference (PMID:25799074, PMID:26942307, PMID:35865993). BAZ2B binds promoter regions to reduce chromatin accessibility and repress PPARα pathway genes in hepatocytes, enhances IRF4 transcription to promote M2 macrophage polarization, and sustains H3K4me3 at myofibroblast activation gene promoters to drive TGF-β1-induced extracellular matrix production (PMID:40389730, PMID:32712329, PMID:41979565). BAZ2B-containing remodeling complexes also suppress G-quadruplex DNA formation at transcriptional regulatory elements, limiting G4-associated genomic instability (PMID:38000389).

1. 2015 High

   Structural characterization of the BAZ2B bromodomain established that it engages acetylated lysine via a shallow, canonical pocket amenable to small-molecule inhibition, providing the first atomic-resolution framework for understanding BAZ2B's histone-reading mechanism.

   Evidence Crystal structures of BAZ2B bromodomain with GSK2801 and BAZ2-ICR inhibitors, ITC binding assays, and FRAP displacement from acetylated chromatin

   PMID:25719566 PMID:25799074

   Open questions at the time

   • Endogenous histone mark selectivity not systematically profiled
   • No information on non-bromodomain regions or full-length protein function
   • In vivo relevance of bromodomain-acetyl-lysine interaction untested
2. 2016 High

   Identification of Tyr1901 as a critical pocket residue mediating water-bridged hydrogen bonds and stereoselectivity refined the molecular basis for acetyl-lysine recognition, explaining bromodomain selectivity.

   Evidence Fragment soaking X-ray crystallography with chiral ligands and computational docking

   PMID:26942307

   Open questions at the time

   • Contribution of Tyr1901 not tested by mutagenesis in cellular context
   • Relative selectivity for specific acetylated histone peptides undefined
3. 2020 Medium

   BAZ2B was shown to function as an H3K14ac reader that promotes IRF4 transcription in macrophages, establishing its first defined transcriptional target and linking it to immune cell polarization.

   Evidence ChIP, RNase protection, knockdown in macrophages and mouse model

   PMID:32712329

   Open questions at the time

   • Whether BAZ2B directly binds H3K14ac at the IRF4 locus versus acting indirectly not fully resolved
   • Requirement for the bromodomain in IRF4 regulation not tested with domain mutants
   • Mechanism of lnc-BAZ2B stabilization of BAZ2B pre-mRNA not elucidated
4. 2022 High

   Structural and biochemical characterization of the TAM domain revealed it adopts a fold similar to BAZ2A and binds dsDNA without methyl-cytosine preference, defining a second chromatin-reading module in BAZ2B.

   Evidence X-ray crystallography of TAM domain and DNA binding affinity measurements

   PMID:35865993

   Open questions at the time

   • Genomic loci bound by the TAM domain in cells not mapped
   • Cooperation between TAM and bromodomain in chromatin targeting not tested
5. 2024 Medium

   BAZ2B was identified as a regulatory subunit of BRF1/BRF5 chromatin remodeling complexes; cancer-associated bromodomain mutations alter histone code recognition, and depletion perturbs transcription and cell morphology without global chromatin reorganization, establishing BAZ2B as a gene-specific transcriptional modulator rather than a global chromatin architect.

   Evidence Domain biochemistry, super-resolution microscopy, transcriptomics, and Hap1 cell knockdown

   PMID:38000389

   Open questions at the time

   • Stoichiometry and assembly pathway of BRF1/BRF5 complexes with BAZ2B not defined
   • Direct effects of cancer mutations on remodeling activity in vitro not measured
   • Mechanism by which BAZ2B selects specific genomic loci unclear
6. 2025 Medium

   Direct binding of BAZ2B to PPARα pathway gene promoters was shown to reduce chromatin accessibility and repress lipid metabolism transcription in hepatocytes, with hepatocyte-specific Baz2b loss attenuating senescence and MASH fibrosis in mice, linking BAZ2B to metabolic disease.

   Evidence ATAC-seq, CUT&RUN, hepatocyte-specific Baz2b knockdown in mouse MASH model

   PMID:40389730

   Open questions at the time

   • Whether BAZ2B-mediated repression requires its bromodomain or TAM domain not dissected
   • Upstream signals recruiting BAZ2B to PPARα loci not identified
   • Relevance to human MASH not validated
7. 2026 Medium

   BAZ2B was found to maintain H3K4me3 at myofibroblast activation gene promoters, driving TGF-β1-induced fibroblast-to-myofibroblast differentiation and ECM production, broadening its role to fibrotic remodeling beyond hepatic tissue.

   Evidence RNA-seq, CUT&Tag-seq, fibroblast knockdown/overexpression, mouse intrauterine adhesion model treated with GSK2801

   PMID:41979565

   Open questions at the time

   • Mechanism by which BAZ2B sustains H3K4me3 (direct reader vs. recruitment of methyltransferase) not resolved
   • Specificity of GSK2801 effects in vivo not fully controlled for off-target BAZ2A inhibition

• Key unresolved questions include how BAZ2B's bromodomain, TAM, and AT-hook domains cooperate to select specific genomic loci, how BRF1/BRF5 complex assembly is regulated, and whether BAZ2B suppression of G-quadruplex structures is mechanistically coupled to its remodeling activity or represents an independent function.
• No reconstituted biochemical system demonstrating BAZ2B-dependent chromatin remodeling in vitro
• Cooperative domain usage in full-length protein not characterized structurally
• Functional consequence of HERC2 interaction for BAZ2B stability or activity unknown