PROBING THE IMPORTANCE OF MBD2 IN THE LOCALIZATION AND FORMATION OF THE NURD COMPLEX

The Nucleosome Remodeling and Deacetylase (NuRD) complex is an important component of gene regulation and successful fetal development. NuRD forms a multivalent interaction with DNA, nucleosomes, histone tails, and additional accessory transcription factors and proteins. Through these interactions NuRD is localized to genomic regions and in particular the beta-globin locus. One protein colocalized with NuRD at this locus is the eight-twenty-one 2 (ETO2) protein. ETO2 forms an oligomer with multiple C-terminals domain binding to many individual PPPL peptide motif. The NuRD protein GATAD2A has a region of four sequential PPPL motifs each independently providing relatively weak binding. Oligomerization of ETO2 allows for increased binding of GATAD2A sufficient for NuRD interaction and a mechanism for genomic recruitment. Likewise, a major architectural protein of NuRD, the methyl-CpG binding domain 2 (MBD2) protein preferentially binds to methylated over unmethylated DNA CpG sites. In contrast, the MBD3 protein does not have this mCpG preference each forming distinct NuRD complexes. Thus, MBD2 localization of NuRD is to genomic regions that are rich in mCpGs even with a handful of sites. Deletion of MBD2 causes increased expression of fetal gamma-globin in adult erythroid cells. Further, the MBD2 intrinsically disordered region (IDR) is a necessary and sufficient protein region forming a critical interaction in NuRD. Thus, targeted disruption of the MBD2-IDR alone could turn gamma-globin expression back on to treat patients with beta-hemoglobinopathies. The IDR interacts with the structurally symmetric histone deacetylase core complex (HDCC). Through IDR mutagenesis, two arginine residues make critical interactions with the HDCC. Based on a structural model generated by the machine learning software AlphaFold, these arginine side chains are positioned in symmetrically related and negatively charged pockets of the HDCC. Thus, successful drug targeting of these HDCC pockets could provide a mechanism for disrupting the NuRD complex as a therapeutic to treat beta-hemoglobinopathies.