Molecular investigation of the TTD and PHD histone binding domains of the epigenetic regulator UHRF2.

UHRF1 and UHRF2 are epigenetic proteins that regulate both histone and DNA methylation and appear to have associated functions in cancer development. Recently, there has been interest in identifying anti-cancer molecules that target these proteins. Both proteins contain TTD and PHD histone binding domains that interact with the H3 tail that is trimethylated on lysine 9 (H3K9me3). In this study, we performed a systematic investigation of the isolated TTD and PHD domains of UHRF2, and compared those results with the histone binding properties of UHRF1. We found that while the PHD of UHRF1 is the main binding contributor, the TTD of UHRF2 has a slightly higher binding affinity for H3K9me3. We also determined that a cage of aromatic amino acids in UHRF2 are essential for H3K9me3 engagement and that an asparagine in the H3R2 binding pocket reduces the electrostatic binding potential between the PHD and the H3 tail. Lastly, we show that a unique ~35 amino acid stretch within the TTD of UHRF2 is a disordered region. Together, we offer insights into the mechanistic differences within the TTD and PHD of UHRF1 and UHRF2, which may be potential avenues for identifying drugs that can selectively target these proteins.