Eukaryotic DNA is compacted into chromatin by association with DNA binding proteins. Nucleosomes are the basic packing unit of chromatin and consist of a protein octamer with two copies of each histone H2A, H2B, H3 and H4. During histone protein synthesis and maturation, these are complexed by specific chaperones. Histone chaperones play an important role in the posttranslational modification of histone proteins, nucleosome assembly, chromatin structure maintenance and transcriptional regulation. Mutation or changes in expression level of various histone chaperones are found in many cancers and have been proposed to promote cancer progression.
We are using NMR to elucidate the mechanisms of various processes mediated by histone chaperones, such as histone processing and folding. By utilizing specialized solution state NMR techniques, we can gain insights into dynamic processes such as histone folding, histone-chaperone and histone-DNA interactions even when these are only transient.
Of particular interest to us is the modulation of enzyme function by histone chaperones. In this context we are looking at the histone acetyltransferase regulator of Ty1 transposition protein 109 (Rtt109). Rtt109 can associate with two different histone chaperones Asf1, resulting in predominantly H3K56 acetylation, and Vps75 resulting in predominantly H3K9, H3K27 and H3K23 acetylation. Using NMR, we are trying to define the histone binding mode and activation mechanism in the presence of both chaperones. In addition, we are exploring the mechanism of other histone chaperones involved in the DNA damage response and histone folding.
Drugs that target proteins involved in epigenetic regulation have recently emerged as promising candidates for cancer therapy and Rtt109 has been proposed as a possible therapeutic approach against opportunistic fungal infections. Detailed structural studies of these proteins will hopefully not only contribute to the understanding of regulation and maintenance of chromatin structure but also provide new targetable interfaces for drug discovery.
Figure from: Histone chaperone exploits intrinsic disorder to switch acetylation specificity, Nature Communications volume 10, Article number: 3435 (2019)