Unravelling the function of protein phosphatases in malaria parasite biology .

Malaria is an infectious disease that causes clinical disease in 500 million humans and results in 1million deaths mainly in children each year. The single cell parasite causing the disease is transmitted by the bite of an infected mosquito and it develops and multiplies first in the liver and then is released into the blood stream, where it infects and multiplies in red blood cells. This blood stage results in the clinical symptoms including high fever and in some cases causes death. In order for the parasite to be transmitted from one person to another it also infects mosquitoes. Parasites undergo complex developmental stages in the different tissues of the mosquito (gut and salivary gland) and the human host (liver and red blood cells). The signals which regulate these processes are not properly understood but studies from other organisms have identified families of enzymes, the protein phosphatases and protein kinases important for such changes. The genome of the malaria parasite contains about 30 genes for protein phosphatases. Recent advances in analysing the function of genes in malaria now allow us the possibility to study the function of these molecules by disrupting each of the genes and observing the consequences. We can see what happens if the proteins in question are no longer made, or if they are tagged with a fluorescent marker we can see where they are located in the parasite under the microscope.
In the present project, parasites lacking these phosphatases will be made and analysed throughout the complete life cycle in both mammalian and insect hosts. Some of the proteins that are essential in the blood stage we will be unable to disrupt. This functional screen will provide a powerful and unique way to prioritise the targets for new drugs against malaria based on understanding the fundamental developmental biology of malaria parasite.

Reversible protein phoshorylation is the major regulatory pathway controlling various cellular processes during the life cycle of an organism. Protein kinases which are responsible for phosphorylation of proteins have been well studied in various eukaryotic systems. However the role of protein phosphatases (PPs) that dephosphorylate proteins is just beginning to emerge. Our recent systematic genome-wide functional analysis of kinases (the kinome) in the malaria parasite has demonstrated the importance of stage specific regulation by various kinases in parasite development. The role of Plasmodium PPs and their complementary function with respect to specific kinases is largely unknown. We propose to characterize PPs in terms of the stage of their expression in the life cycle, their sub-cellular location, and carry out a genome-wide functional analysis of all PPs using reverse genetics in the rodent malaria model, P. berghei. Parasites expressing tagged proteins and gene knockout mutants will be studied in conjunction with the kinase mutants generated in the earlier studies. The main emphasis of the study will be the role of phosphatases in sporogony in terms of sporozoite development, differentiation, motility and invasion. These results will give important insights into the signalling pathways regulating malaria parasite development and will identify phosphatases with an essential function at the asexual blood stage. These data together with those from the kinase study will form a unique resource for identifying potential drug targets and developing novel malaria interventions, and the sporozoite mutants may also serve as genetically attenuated models for developing protective vaccines.