In silico characterization of Plasmodium falciparum purinergic receptor: a novel chemotherapeutic target

Antimalarial and Plasmodium falciparum serpentine receptor 12 targeting effect of FDA approved purinergic receptor antagonist

Intraerythrocytic stages of Plasmodium falciparum responsible for all clinical manifestations of malaria are regulated by array of signalling cascades that represent attractive targets for antimalarial therapy. G-protein coupled receptors (GPCRs) are druggable targets in the treatment of various pathological conditions, however, there is limited understanding about the role of GPCRs in malaria pathogenesis. In Plasmodium, serpentine receptors (PfSR1, PfSR10, PfSR12 and PfSR25) with GPCR-like membrane topology have been reported with the finite knowledge about their potential as antimalarial targets. We analyzed the localization of these receptors in malaria parasite by immunofluorescence assays. All four receptors were expressed in blood stages with PfSR12 expressing more in late intraerythrocytic stages. Further, we evaluated the druggability of PfSR12 using FDA-approved P2Y purinergic receptor antagonist, Prasugrel and its active metabolite R138727, which is proposed to be specific towards PfSR12. Interestingly, biophysical analysis indicated strong binding between PfSR12 and R138727 as compared to the prodrug Prasugrel. This binding interaction was further confirmed by thermal shift assay. Treatment of parasite with Prasugrel and R138727 resulted in growth inhibition of P. falciparum indicating an important role of purinergic signalling and PfSR12 in parasite survival. Next, progression studies indicated the inhibitory effect of Prasugrel begins in late erythrocyte stages corroborating with PfSR12 expression at these stages. Furthermore, Prasugrel also blocked in vivo growth of malaria parasite in a mouse experimental model. This study indicates the presence of P2Y type of purinergic signalling in growth and development of malaria parasite and suggests PfSR12, putative purinergic receptor druggability through Prasugrel.Communicated by Ramaswamy H. Sarma.

Evidence of G-Protein-Coupled Receptors (GPCR) in the Parasitic Protozoa Plasmodium falciparum-Sensing the Host Environment and Coupling within Its Molecular Signaling Toolkit

Throughout evolution, the need for single-celled organisms to associate and form a single cluster of cells has had several evolutionary advantages. In complex, multicellular organisms, each tissue or organ has a specialty and function that make life together possible, and the organism as a whole needs to act in balance and adapt to changes in the environment. Sensory organs are essential for connecting external stimuli into a biological response, through the senses: sight, smell, taste, hearing, and touch. The G-protein-coupled receptors (GPCRs) are responsible for many of these senses and therefore play a key role in the perception of the cells' external environment, enabling interaction and coordinated development between each cell of a multicellular organism. The malaria-causing protozoan parasite, Plasmodium falciparum, has a complex life cycle that is extremely dependent on a finely regulated cellular signaling machinery. In this review, we summarize strong evidence and the main candidates of GPCRs in protozoan parasites. Interestingly, one of these GPCRs is a sensor for K+ shift in Plasmodium falciparum, PfSR25. Studying this family of proteins in P. falciparum could have a significant impact, both on understanding the history of the evolution of GPCRs and on finding new targets for antimalarials.

The endoplasmic reticulum-resident serpentine receptor SR10 has important functions for asexual and sexual blood stage development of Plasmodium falciparum

Serpentine receptors (SRs) are transmembrane proteins generally acting as mediators to facilitate the communication between a cell and its environment. At least six putative SR-like proteins are encoded in the genome of the malaria parasite Plasmodium falciparum. For two of them, roles in cell stress control were reported; however, for most of the SR-like proteins the functions are not yet known. In this study, we provide a first phenotypic analysis of the plasmodial SR10. The transmembrane protein is expressed in the asexual and sexual blood stages of P. falciparum. Co-localization and co-immunoprecipitation assays demonstrated an association of SR10 with the endoplasmic reticulum protein ERC. Gene disruption of SR10 leads to impaired intraerythrocytic replication and strongly reduces gametocyte numbers. We thus propose that SR10 is a protein associated with the endoplasmic reticulum that has important functions for asexual and sexual blood stage development.

CX3CL1 binding protein-2 (CBP2) of Plasmodium falciparum binds nucleic acids

Several exported Plasmodium falciparum (Pf) proteins contribute to malaria biology through their involvement in cytoadherence, immune evasion and host cell remodelling. Many of these exported proteins and other host molecules are present in iRBC (infected red blood cell) generated extracellular vesicles (EVs), which are responsible for host cell modification and parasite development. CX3CL1 binding proteins (CBPs) present on the surface of iRBCs have been reported to contribute to cytoadhesion by binding with the chemokine 'CX3CL1' via their extracellular domains. Here, we have characterized the cytoplasmic domain of CBP2 to understand its function in parasite biology using biochemical and biophysical methods. Recombinant cytoplasmic CBP2 (cCBP2) binds nucleic acids showing interaction with DNA/RNA. cCBP2 shows dimer formation under non-reducing conditions highlighting the role of disulphide bonds in its oligomerization while ATP binding leads to structural changes in the protein. In vitro interaction studies depict its binding with a Maurer's cleft resident protein 'PfSBP1', which is influenced by ATP binding of cCBP2. Our results suggest CBP2 as a two-transmembrane (2TM) receptor responsible for targeting EVs and delivering cargo to host endothelial cells. We propose CBP2 as an important molecule having roles in cytoadherence and immune modulation through its extracellular and cytoplasmic domains respectively.