Ca ²⁺ signals critical for egress and gametogenesis in malaria parasites depend on a multipass membrane protein that interacts with PKG

Abstract

Calcium signaling regulated by the cGMP-dependent protein kinase (PKG) controls key life cycle transitions in the malaria parasite. However, how calcium is mobilized from intracellular stores in the absence of canonical calcium channels in Plasmodium is unknown. Here, we identify a multipass membrane protein, ICM1, with homology to transporters and calcium channels that is tightly associated with PKG in both asexual blood stages and transmission stages. Phosphoproteomic analyses reveal multiple ICM1 phosphorylation events dependent on PKG activity. Stage-specific depletion of Plasmodium berghei ICM1 prevents gametogenesis due to a block in intracellular calcium mobilization, while conditional loss of Plasmodium falciparum ICM1 is detrimental for the parasite resulting in severely reduced calcium mobilization, defective egress, and lack of invasion. Our findings suggest that ICM1 is a key missing link in transducing PKG-dependent signals and provide previously unknown insights into atypical calcium homeostasis in malaria parasites essential for pathology and disease transmission.

Plasmodium falciparum Calcium-Dependent Protein Kinase 4 is Critical for Male Gametogenesis and Transmission to the Mosquito Vector

“…Gametogenesis within the mosquito midgut may be triggered by a combination of factors, including drop in temperature ( 4 , 5 ), increase in pH ( 5 ), and/or exposure to xanthurenic acid (XA), a metabolite of tryptophan ( 6 , 7 ). Gametogenesis is also linked to mobilization of intracellular calcium (Ca 2+ ) stores, which can regulate Ca 2+ -dependent protein function ( 8 , 9 ). The P. falciparum genome encodes seven distinct calcium-dependent protein kinases (CDPKs), which are key Ca 2+ effectors in the parasite that have roles throughout the Plasmodium life cycle ( 10 ).…”

Functional Analysis of the Expanded Phosphodiesterase Gene Family in Toxoplasma gondii Tachyzoites

“…Catalytically active PKG is required for microneme secretion and motility by stimulating Ca 2+ flux, and through an unknown mechanism that cannot be bypassed by exogenous Ca 2+ (28)(29)(30)(31)(32)(33)(34). PKG is thought to stimulate release of Ca 2+ stores by upregulating inositol 1,4,5-trisphosphate (IP3) signaling and by phosphorylating ICM1, a multipass membrane protein essential for PKG-dependent calcium mobilization (35). Cytosolic Ca 2+ activates Ca 2+ -binding proteins that regulate microneme secretion (e.g.…”

Calcium in the Backstage of Malaria Parasite Biology

“…More recently, PKG was found to interact with and phosphorylate a multipass membrane protein, termed as important for Ca 2+ mobilization 1 (ICM1). Conditional knockdown of ICM1 revealed an essential role in Ca 2+ mobilization to initiate both Plasmodium gametogenesis and merozoite egress ( Balestra et al., 2021 ). Additionally, guanylyl-cyclase alpha (GCα)-null mutant parasites were unable to synthesize cGMP for PKG activation in schizonts, leading to a reduction in Ca 2+ release from internal stores ( Nofal et al., 2021 ).…”