Chromatin proteomics reveals a dynamic histone code as novel druggable system essential to malaria parasite differentiation

Abstract

The malaria causing parasite, Plasmodium falciparum, remains one of the deadliest organisms globally. Underlying its unique and complex biology that is divergent from other higher-order eukaryotes, lies a weak spot: its epigenome. Histone post-translational modifications (PTMs) are dynamically deposited and removed during the parasite's proliferative asexual intra-erythrocytic developmental cycle and sexual differentiation process to form an overall pattern of histone PTMs that co-exist at specific times. Emerging evidence in eukaryotic gene regulation suggests that histone PTMs do not only function alone but can combine to ultimately signal for a biological outcome that is different from the PTM alone. In this thesis, I explore the combinatorial histone code of P. falciparum parasites. Histone PTM combinations are mapped across asexual, early- and late-stage gametocytes to reveal a highly complex “code” that defines each stage. Evidence for the functional relationship between histone PTMs is provided. Since the functional relevance of combinatorial PTMs relies on the effector proteins that bind to them, the proteome associated with histone PTMs that co-exist in the parasite is identified to reveal the association of a unique epigenetic complex that is recruited to each of the PTMs in combination. Lastly, the biological importance of crosstalk between histone PTMs is probed with chemical interference of the effector proteins that establish the combinations. This revealed that gametocytes are particularly susceptible to crosstalk inhibition by proxy and that arginine methylation is likely critical for gametocyte specific biological processes. Ultimately, this thesis presents fundamental and preliminary evidence of the functional importance of the histone code in P. falciparum, a feature that reshapes our understanding of gene regulation in P. falciparum well beyond the central dogma of biology.