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Plasmodium falciparum protein kinase CK2

Holland, Zoe (2008) Plasmodium falciparum protein kinase CK2. PhD thesis, University of Glasgow.

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Abstract

Malaria, caused by infection with intracellular protozoan parasites of the genus Plasmodium, is responsible for 300 to 600 million clinical cases annually (Snow et al., 2005), resulting in the deaths of up to three million people every year (Breman, 2001, Breman et al., 2004). There is a clear need for further research aimed at identifying novel drug targets (Ridley, 2002). Reversible phosphorylation of proteins is a major regulatory mechanism in most cellular processes, and protein kinases are considered promising drug targets, comprising as much as 30% of all protein targets under investigation (Cohen, 2002). The divergences between human and plasmodial protein kinases suggest that specific inhibition of the latter is an achievable goal (Doerig, 2004, Doerig and Meijer, 2007). This study investigates protein kinase CK2 of Plasmodium falciparum, seeking to establish by reverse genetics and biochemical approaches whether it represents a possible antimalarial drug target. Protein-kinase CK2, formerly known as Casein Kinase II, is a dual-specificity (Serine/Threonine and Tyrosine) protein kinase ubiquitously expressed in eukaryotes. It has over 300 cellular substrates catalogued to date (Meggio and Pinna, 2003). Consistent with its multiple substrates, the enzyme plays a crucial role in many cellular processes, and is essential to viability in yeast and slime mould (Padmanabha et al., 1990, Kikkawa et al., 1992). The human CK2 holoenzyme consists of two catalytic a or a’ subunits and two regulatory b subunits, and recent evidence indicates that the latter interact with several protein kinases in addition to CK2a (reviewed in (Bibby and Litchfield, 2005)), pointing to a likely role in the integration of numerous signalling pathways. A putative CK2a orthologue and two predicted CK2b subunits were identified in the P. falciparum genome (Ward et al., 2004, Anamika et al., 2005). Here we present the biochemical characterisation of the PfCK2a orthologue and both PfCK2b orthologues, and demonstrate by using a reverse genetics approach that each of the three subunits is essential for completion of the erythrocytic asexual cycle of the parasite, thereby validating the enzyme as a possible drug target. Recombinant PfCK2a possesses protein kinase activity, exhibits similar substrate and co-substrate preferences to those of CK2a subunits from other organisms, and interacts with both of the PfCK2b subunits in vitro. PfCK2a is amenable to inhibitor screening, and we report differential susceptibility between the human and P. falciparum CK2a enzymes to a small molecule inhibitor. Taken together, the data indicate that PfCK2a is an attractive, validated target for antimalarial chemotherapeutic intervention.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Plasmodium, malaria, kinase, biochemical characterisation, reverse genetics
Subjects: Q Science > QH Natural history > QH301 Biology
Q Science > QH Natural history > QH426 Genetics
Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Infection Immunity and Inflammation
Supervisor's Name: Doerig, Prof. Christian
Date of Award: 2008
Depositing User: Miss Zoe Holland
Unique ID: glathesis:2008-606
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 Mar 2009
Last Modified: 10 Dec 2012 13:20
URI: http://theses.gla.ac.uk/id/eprint/606

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