Gametogenesis in Malaria Parasites Is Mediated by the cGMP-Dependent Protein Kinase

Abstract

Malaria parasite transmission requires differentiation of male and female gametocytes into gametes within a mosquito following a blood meal. A mosquito-derived molecule, xanthurenic acid (XA), can trigger gametogenesis, but the signalling events controlling this process in the human malaria parasite Plasmodium falciparum remain unknown. A role for cGMP was revealed by our observation that zaprinast (an inhibitor of phosphodiesterases that hydrolyse cGMP) stimulates gametogenesis in the absence of XA. Using cGMP-dependent protein kinase (PKG) inhibitors in conjunction with transgenic parasites expressing an inhibitor-insensitive mutant PKG enzyme, we demonstrate that PKG is essential for XA- and zaprinast-induced gametogenesis. Furthermore, we show that intracellular calcium (Ca2+) is required for differentiation and acts downstream of or in parallel with PKG activation. This work defines a key role for PKG in gametogenesis, elucidates the hierarchy of signalling events governing this process in P. falciparum, and demonstrates the feasibility of selective inhibition of a crucial regulator of the malaria parasite life cycle.

The kinomes of apicomplexan parasites

“…Compound 1 was subsequently shown to inhibit P. falciparum proliferation in vitro [44]. The effect of Compound 1 on blood-stage schizogony has recently revealed that cGMP signaling and PfPKG play a central role in both asexual and sexual development of P. falciparum [7,45]. The role of PKG in regulating the malaria parasite's life cycle progression has recently been reviewed by Hopp et al (Hopp et al in press, and see pages XX in this issue).…”

“…Many PKs of parasitic organisms show a profound structural and functional divergence from their orthologues in the infected hosts (when they exist), suggesting that parasite-specific inhibition might be achieved. A striking example is given by the elegantly documented selective inhibition allowed by small gatekeeper residues displayed by some kinases from apicomplexan parasites [6][7][8][9].…”

Phospholipases during membrane dynamics in malaria parasites

“…Initially, a plasmodial guanylyl cyclase becomes activated, leading to the synthesis of cyclic GMP (cGMP) (Carucci et al, 2000;Muhia et al, 2001). The rise of cGMP activates the cGMP-dependent protein kinase G, which regulates the generation of PIP 2 (Alam et al, 2015;Brochet et al, 2014;McRobert et al, 2008). At the same time, PI-PLC is stimulated, which hydrolyses PIP 2 to generate DAG and IP 3 (Martin et al, 1994;Raabe et al, 2011b), resulting in the release of calcium from internal stores (Billker et al, 2004).…”

Does protein phosphorylation govern host cell entry and egress by the Apicomplexa?

“…A conditional disruption of PbPKG in sporozoites leads to a severe intracellular block in the liver stage, although the mutated sporozoites were still able to invade (Falae et al, 2010). PfPKG is also implicated in mediating differentiation of male and female gametocytes into mature gametes within the mosquito (McRobert et al, 2008). Treatment of P. falciparum ring stage with compound 1 allowed normal development up to 30 h post infection (pi), and segmented schizonts were able to form.…”