Structure and DNA binding analysis of AT-rich interaction domain present in human BAF-B specific subunit BAF250b.

BAF250b and its paralog BAF250a are the DNA-binding central hub proteins present in BAF-B and BAF-A classes of SWI/SNF chromatin-remodeling complexes. BAF250b contains an AT-rich interaction domain (ARID) and C-terminal BAF250_C domain, and it is found mutated in several cancers. ARID is a conserved helix-turn-helix motif-containing DNA-binding domain present in several eukaryotic proteins. The ARID of BAF250b has been proposed to play roles in recruiting SWI/SNF to the target gene promoters for their activation. BAF250b ARID structures had been deposited in the protein data bank by a structural genomics consortium. However, it is not well-studied for its DNA-binding and solution dynamic properties. Here, we report complete backbone NMR resonance assignments of human BAF250b ARID. NMR chemical shifts and the backbone dynamics showed that the solution structure of the protein matched the reported crystal structures. The structure and chemical shift indexing revealed the presence of a short β-sheet in the DNA-binding region of BAF250b ARID that was absent in the structure of its paralog BAF250a ARID. NMR chemical shift perturbations identified DNA-binding residues and revealed the DNA-binding interface on BAF250b ARID. NMR data-driven HADDOCK models of BAF250b ARID - DNA complexes revealed its plausible mode of DNA-binding. Isothermal titration calorimetry experiments showed that BAF250b ARID interacts with DNA sequences with moderate affinities like BAF250a ARID. However, distinct thermodynamic signatures were observed for binding of BAF250a ARID and BAF250b ARID to AT-rich DNA sequence, suggesting that subtle sequence and structural differences in these two proteins influence their DNA-binding.