A Novel Lipid (Phosphatidylthreonine)-Regulated Calcium Homeostasis in Toxoplasma Gondii
The major membrane glycerophospholipid classes, described thus far, include phosphatidylcholine,
phosphatidylethanolamine, phosphatidylserine (PtdSer) and phosphatidylinositol. Our recent work has
demonstrated the natural occurrence and genetic origin of an exclusive and rather abundant lipid
phosphatidylthreonine (PtdThr) in a widespread and clinically relevant eukaryotic model parasite
Toxoplasma gondii. Of note is the fact that PtdThr is a natural homolog of the otherwise-universal
PtdSer, which is long known to control Ca2+ homeostasis in mammalian cells. Our earlier work showed
that targeted genetic disruption of phosphatidylthreonine synthase (PTS) impairs the lytic cycle and
virulence of the parasite due to unforeseen attenuation of the consecutive events of motility, egress
and invasion. Using a calcium biosensor, we observed that loss of PtdThr causes a dysregulation of
cytosolic calcium that in turn translates into a defective gliding motility. In this proposal, we aim to
examine the mechanistic regulation of calcium homeostasis by PtdThr using an approach spanning
across the disciplines of biochemistry, gene engineering, cell biology and synthetic chemistry. In brief,
we will determine the levels of calcium in the cytosol and endoplasmic reticulum (i.e. site of PtdThr and
PtdSer synthesis) of the PTS-mutant by expressing a gene-encoded sensor. Assays involving genetic
or chemical modulation of calcium homeostasis, and genetic restoration of lipid perturbation in the
PtdThr-mutant will be done to establish a role of lipids in calcium regulation. In parallel, we will identify
PtdSer/PtdThr-binding proteins underlying Ca2+ regulation by click-chemistry and mass spectrometry,
followed by making of selected parasite mutants and phenotyping. Equally, subcellular distribution of
PtdThr and PtdSer will be detected using synthetic chemical probes and customized lipid biosensors
via high-resolution imaging. Not least, physiological importance of the key PtdThr species in T. gondii
will be investigated by chemical complementation of the parasite cultures. Upon completion, we shall
understand the roles of PtdThr (and PtdSer) in calcium homeostasis during asexual reproduction of T.
gondii, which can eventually be exploited to inhibit the parasite growth.
Financer
DFG: Sachbeihilfe
Duration of project
Start date: 02/2019
End date: 01/2022
Research Areas
Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology
