The ubiquitous second messenger cAMP mediates signal transduction processes in the malarial parasite that regulate host erythrocyte invasion and the proliferation of merozoites. In Plasmodium falciparum the central receptor for cAMP is the single regulatory subunit ® of Protein kinase A (PKA). To aid the development of compounds that can selectively dysregulate parasite PKA signalling we solved the structure of the PKA regulatory subunit in complex with cAMP and a related analog that displays antimalarial activity: Sp-2Cl-cAMPS. Prior to signalling, PKA-R holds the kinases catalytic subunit © in an inactive state by exerting an allosteric inhibitory affect. When two cAMP molecules bind to PKA-R they stabilise a structural conformation that facilitates its dissociation, freeing PKA-C to phosphorylate down-stream substrates such as Apical Membrane Antigen 1. We show that untimely induction of this response with membrane permeable Sp-2Cl-cAMPS blocks parasite proliferation via a PKA-R dependent mechanism.
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This work was performed with the help of the staff of the Australian synchrotron MX1 and
MX2 beamlines. We appreciate support from the National Health and Medical Research Council
of Australia (NHMRC) Project grant (APP1068287) and funding from the Victorian Operational
Infrastructure Support Program received by the Burnet Institute. We thank the Australian Red
Cross Blood Bank for the provision of human blood.