Involvement of Plasmodium falciparum protein kinase CK2 in the chromatin assembly pathway
- Equal contributors
1 Biology of Host-Parasite Interactions Unit, Institut Pasteur, 25 rue du Dr. Roux, F-75724 Paris, France
2 CNRS URA2581, 25 rue du Dr. Roux, F-75724 Paris, France
3 Inserm-EPFL Joint Laboratory, Global Health Institute, EPFL-SV-GHI, Station 19, CH-1015 Lausanne, Switzerland
4 Wellcome Trust Centre for Molecular Parasitology, University of Glasgow, Glasgow G12 8TA, Scotland, UK
5 International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, 110 067 New Delhi, India
6 Proteomics Core Facility, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
7 Department of Microbiology, Building 76, Monash University, Wellington Road, Clayton, VIC 3800, Australia
BMC Biology 2012, 10:5 doi:10.1186/1741-7007-10-5Published: 31 January 2012
Protein kinase CK2 is a pleiotropic serine/threonine protein kinase with hundreds of reported substrates, and plays an important role in a number of cellular processes. The cellular functions of Plasmodium falciparum CK2 (PfCK2) are unknown. The parasite's genome encodes one catalytic subunit, PfCK2α, which we have previously shown to be essential for completion of the asexual erythrocytic cycle, and two putative regulatory subunits, PfCK2β1 and PfCK2β2.
We now show that the genes encoding both regulatory PfCK2 subunits (PfCK2β1 and PfCK2β2) cannot be disrupted. Using immunofluorescence and electron microscopy, we examined the intra-erythrocytic stages of transgenic parasite lines expressing hemagglutinin (HA)-tagged catalytic and regulatory subunits (HA-CK2α, HA-PfCK2β1 or HA-PfCK2β2), and localized all three subunits to both cytoplasmic and nuclear compartments of the parasite. The same transgenic parasite lines were used to purify PfCK2β1- and PfCK2β2-containing complexes, which were analyzed by mass spectrometry. The recovered proteins were unevenly distributed between various pathways, with a large proportion of components of the chromatin assembly pathway being present in both PfCK2β1 and PfCK2β2 precipitates, implicating PfCK2 in chromatin dynamics. We also found that chromatin-related substrates such as nucleosome assembly proteins (Naps), histones, and two members of the Alba family are phosphorylated by PfCK2α in vitro.
Our reverse-genetics data show 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.