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A Protein Kinase G -interacting protein regulates critical calcium signals in malaria parasites (Co-IP)

ABSTRACT: In malaria parasites, cGMP signalling is mediated by a single cGMP-dependent protein kinase (PKG) . One of the major functions of PKG is to control calcium signals essential for the parasite to exit red blood cells or for the transmission of the gametocyte stages to the mosquito . However, how PKG controls these signals in the absence of known second messenger-dependent calcium channels or scaffolding proteins remains a mystery. Here we use pull-down approaches to identify a PKG partner protein in both Plasmodium falciparum schizonts and P. berghei gametocytes. This partner, named ICM1, is a polytopic membrane protein with homologies to transporters and calcium channels, raising the possibility of a direct functional link between PKG and calcium homeostasis. Phosphoproteomic analyses in both Plasmodium species highlight a densely phosphorylated region of ICM1 with multiple phosphorylation events dependent on PKG activity. Conditional disruption of the P. falciparum ICM1 gene results in reduced cGMP-dependent calcium mobilisation associated with defective egress and invasion. Stage-specific depletion of ICM1 in P. berghei gametocytes blocks gametogenesis due to the inability of mutant parasites to mobilise intracellular calcium upon PKG activation. These results provide us with new insights into the atypical calcium homeostasis in malaria parasites.

INSTRUMENT(S): Orbitrap Fusion Lumos, Q Exactive

ORGANISM(S): Plasmodium Berghei Anka

TISSUE(S): Gametocyte

SUBMITTER: alexandre Hainard

LAB HEAD: Mathieu Brochet

PROVIDER: PXD020210 | Pride | 2021-01-25

REPOSITORIES: Pride

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Project description:For malaria transmission, the parasite must undergo sexual differentiation into mature gametocytes. However, the molecular basis for this critical transition in the parasites life cycle is unknown. Six previously uncharacterized genes, Pfg14.744, Pfg14.745, Pfg14.748, Pfg14.763, Pfg14.752 and Pfg6.6 that are members of a 36 gene Plasmodium falciparum-specific subtelomeric superfamily were found to be expressed in parasites that are committed to sexual development as suggested by co-expression of Pfs16 and Pfg27. Northern blots demonstrated that Pfg14.744 and Pfg14.748 were first expressed before the parasites differentiated into morphologically distinct gametocytes, transcription continued to increase until stage II gametocytes were formed and then rapidly decreased. Immunofluorescence assays indicated that both proteins were only produced in the subpopulation of ring stage parasites that are committed to gametocytogenesis and both localized to the parasitophorous vacuole (PV)b of the early ring stage parasites. As the parasites continued to develop Pfg14.748 remained within the parasitophorous vacuole, while Pfg14.744 was detected in the erythrocyte. The 5' flanking region of either gene alone was sufficient to drive early gametocyte specific expression of green fluorescent protein (GFP). In parasites transfected with a plasmid containing the Pfg14.748 5' flanking region immediately upstream of GFP, fluorescence was observed in a small number of schizonts the cycle before stage I gametocytes were observed. This expression pattern is consistent with commitment to sexual differentiation prior to merozoite release and erythrocyte invasion. Further investigation into the role of these genes in the transition from asexual to sexual differentiation could provide new strategies to block malaria transmission. Microarray analysis was used to compare two clones derived from Plasmodium falciparum strain 3D7 parasites that differ in their ability to undergo gametocytogenesis. Clone G+ produces gametocytes and clone G- produces very few if any gametocytes. RNA was harvested from the cultures when the asexual parasitemia was 0.9-1.48% (day 4) (n=4) after setting up the gametocyte cultures and 5.2-5.58% (day 6) (n=4) prior to the appearance of morphologically distinct gametocytes and used to generate cDNA that was labeled with Cy3 or Cy5 and hybridized to the Plasmodium falciparum 70 mer oligonucleotide microarray developed by DeRisi and co-workers.

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A Protein Kinase G -interacting protein regulates critical calcium signals in malaria parasites (Co-IP)

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