Structural comparisons reveal diverse binding modes between nucleosome assembly proteins and histones

Nucleosome assembly proteins (NAPs) are histone chaperones that play a central role in facilitating chromatin assembly/disassembly which is of fundamental importance for DNA replication, gene expression regulation, and progression through the cell cycle. In vitro, NAPs bind to the core histones H2A, H2B, H3, H4 and possibly to H1. The NAP family contains well-characterized and dedicated histone chaperone domain called the NAP domain, and the NAP–histone interactions are key to deciphering chromatin assembly. Our comparative structural analysis of the three three-dimensional structures of NAPs from S. cerevisiae, C. elegans, and A. thaliana in complex with the histone H2A–H2B dimer reveals distinct and diverse binding of NAPs with histones. The three NAPs employ distinct surfaces for recognizing the H2A–H2B dimer and vice versa. Though histones are highly conserved across species they display diverse footprints on NAPs. Our analysis indicates that understanding of NAPs and their interaction with histone H2A–H2B remains sparse. Due to divergent knowledge from the current structures analyzed here, investigations into the dynamic nature of NAP–histone interactions are warranted.