Rapid kinetics of lipid second messengers controlled by a cGMP signalling network coordinates apical complex functions inToxoplasmatachyzoites

Abstract

Host cell invasion and subsequent egress by Toxoplasma parasites is regulated by a network of cGMP, cAMP, and calcium signalling proteins. Such eukaryotic signalling networks typically involve lipid second messengers including phosphatidylinositol phosphates (PIPs), diacylglycerol (DAG) and phosphatidic acid (PA). However, the lipid signalling network in Toxoplasma is poorly defined. Here we present lipidomic analysis of a mutant of central flippase/guanylate cyclase TgGC in Toxoplasma, which we show has disrupted turnover of signalling lipids impacting phospholipid metabolism and membrane stability. The turnover of signalling lipids is extremely rapid in extracellular parasites and we track changes in PA and DAG to within 5 seconds, which are variably defective upon disruption of TgGC and other signalling proteins. We then identify the position of each protein in the signal chain relative to the central cGMP signalling protein TgGC and map the lipid signal network coordinating conoid extrusion and microneme secretion for egress and invasion.

The Extracellular Milieu of Toxoplasma 's Lytic Cycle Drives Lab Adaptation, Primarily by Transcriptional Reprogramming

“…Phospholipid flipping activity is of great biological importance for the biogenesis of vesicles ( 50 , 51 ), creating a fusion-competent bilayer ( 52 ), maintaining membrane stability ( 53 , 54 ), and generating signaling cues ( 55 – 57 ). It was recently reported that this particular Toxoplasma P4-flippase localizes to the endoplasmic reticulum ( 58 ), while the HyperLOPIT proteome assigned it to the Golgi-plasma membrane ( 27 ). Dissecting how the flippase SNPs modulate the kinetics or substrate preference will require extensive further work.…”

The extracellular milieu ofToxoplasma’s lytic cycle drives lab-adaptation and promotes changes in lipid metabolism primarily driven by transcriptional reprogramming

“…Indeed, secretory pathway genes also trend up during evolution (Figure 7a). It was recently reported this particular Toxoplasma P4-flippase localizes to the ER [56], while a whole parasite organelle proteomic approach assigned it to the a dynamic Golgi/PM localization [30]. Dissecting how the flippase SNPs modulate the kinetics or substrate preference will require extensive further work.…”

The flexibility of Apicomplexa parasites in lipid metabolism

“…Briefly, both enzymes can generate cGMP, which activates PKG and a signaling cascade, which includes calcium release and activation of calcium-dependent proteins kinases (CDPKs). The flippase domain of GCs are known to be essential; however, their exact mechanism in the above mentioned process is unclear [ 55 , 84 , 85 ]. In a study that monitored the in vitro virulence traits of a lab-adapted T .…”