Structure and function of the BAH domain in chromatin biology

Proteins containing Bromo Adjacent Homology (BAH) domain are often associated with biological processes involving chromatin, and mutations in BAH domains have been found in human diseases. A number of structural and functional studies have revealed that the BAH domain plays diverse and versatile roles in chromatin biology, including protein–protein interactions, recognition of methylated histones and nucleosome binding. Here we review recent developments in structural studies of the BAH domain, and intend to place the structural results in the context of biological functions of the BAH domain-containing proteins. A converging theme from the structural studies appears that the predominantly β-sheet fold of the BAH domain serves as a scaffold, and function-specific structural features are incorporated at the loops connecting the β-strands and surface-exposed areas. The structures clearly specified regions critical for protein–protein interactions, located the position of methyllysine-binding site and implicated areas important for nucleosome binding. The structural results provided valuable insights into the molecular mechanisms of BAH domains in molecular recognitions, and the information should greatly facilitate mechanistic understanding of BAH domain proteins in chromatin biology.