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Involvement of Plasmodium falciparum protein kinase CK2 in the chromatin assembly pathway.
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Edité par CCSD ; BioMed Central -
International audience. ABSTRACT: BACKGROUND: Protein kinase CK2 is a pleiotropic serine/threonine protein kinase with hundreds of reported substrates. The kinase plays important role in a number of cellular processes. The cellular functions of Plasmodium falciparum protein kinase CK2 (PfCK2) are unknown. The parasite's genome encodes one catalytic subunit, PfCK2, which we have previously shown to be essential for completion of the asexual erythrocytic cycle, and two putative regulatory subunits, PfCK21 and PfCK22. RESULTS: We now show that the genes encoding both regulatory PfCK2 subunits, PfCK2beta1 and PfCK2beta2, cannot be disrupted. By examining intra-erythrocytic stages of transgenic parasite lines expressing HA-tagged catalytic and regulatory subunits (HA-CK2alpha, HA-PfCK2beta1 or HA-PfCK2beta2) by immunofluorescence and electron microscopy, we localize all three subunits to both cytoplasmic and nuclear compartments of the parasite. The same transgenic parasite lines were used to purify PfCK2beta1- and PfCK2beta2-containing complexes, which were analyzed by mass spectrometry. Recovered proteins were unevenly distributed between various pathways, with a large proportion of components of the chromatin assembly pathway being present in both PfCK2beta1 and PfCK2beta2 precipitates, implicating PfCK2 in chromatin dynamics. We further demonstrate that chromatin-related substrates such as nucleosome assembly proteins (Naps), histones, and two members of the Alba family are indeed phosphorylated by PfCK2alpha in vitro. CONCLUSIONS: Our reverse genetics data demonstrate that each of the two regulatory PfCK2 subunits is required for completion of the asexual erythrocytic cycle. Our interactome study points to an implication of PfCK2 in many cellular pathways, with chromatin dynamics being identified as a major process regulated by PfCK2. This study paves the way for a kinome-wide interactomics-based approach to elucidate protein kinase function in malaria parasites.
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