Post-translational modification of H2B C-terminal helix regulates nucleosome interactions and chromatin signaling.

Histone H2B contains a highly conserved C-terminal (H2B αC) helix that has been implicated in chromatin interactions and dynamics. The H2B αC helix comprising residues 105-125 is positioned adjacent to a major site of nucleosome interactions called the acidic patch. Despite individual structural studies highlighting interactions between chromatin proteins and the H2B αC helix, the general role of the helix in mediating nucleosome recognition has not been explored. Moreover, many post-translational modifications (PTMs) have been identified within the H2B αC helix, but significant gaps exist in our understanding of their regulatory potential. In this study, we employed nucleosome affinity proteomics using a library of nucleosomes with mutations or PTMs of the H2B αC helix to investigate contributions to nucleosome binding. Our work uncovers new spatial patterns of H2B αC helix engagement across the proteome. We also demonstrate that H2B K120 mono-ubiquitylation (H2B K120ub) within the H2B αC helix broadly disrupts nucleosome binding, phenocopying mutation of the acidic patch, while differentially regulating acidic patch-dependent chromatin functions. In contrast, lysine acetylation results in more subtle position-specific changes, highlighting a more general role of H2B αC helix PTMs in tuning acidic patch recognition.