Treeck, M. — Page 2 | bioRxiv Science

bioRxiv2019

Differential requirements of cyclase associated protein (CAP) for actin turnover during the lytic cycle of Toxoplasma gondii

Toxoplasma gondii contains a limited subset of actin binding proteins. Here we show that ablation of the putative actin regulator cyclase-associated protein (TgCAP) leads to significant defects in some but not all actin dependent processes, including a defect in cell-cell communication, but surprisingly not synchronicity of division. Two CAP isoforms originate from alternative translational start sites and are beneficial for parasite fitness while a single isoform is sufficient for virulence in mice. Examination of the mutant parasites by 3D electron microscopy reveals that loss of CAP results in a defect to form a normal residual body, but all parasites remain connected within the vacuole. This dissociates synchronicity of division and parasite rosetting and reveals that establishment and maintenance of the residual body may be more complex than previously thought. These results highlight the different spatial requirements for actin turnover in Toxoplasma, controlled by a reduced subset of actin binding proteins.

microbiology↗

bioRxiv2018

A divergent kinase lacking the glycine-rich loop regulates membrane ultrastructure of the Toxoplasma parasitophorous vacuole

Apicomplexan parasites replicate within a protective organelle called the parasitophorous vacuole (PV). The Toxoplasma gondii PV is filled with a network of tubulated membranes, which are thought to facilitate trafficking of effectors and nutrients. Despite being critical to parasite virulence, there is scant mechanistic understanding of the networks functions. Here, we identify the parasite secreted kinase WNG1 as a critical regulator of tubular membrane biogenesis. WNG1 family members adopt an atypical protein kinase fold lacking the glycine rich ATP-binding loop that is required for catalysis in canonical kinases. Unexpectedly, we find that WNG1 is an active protein kinase that localizes to the PV lumen and phosphorylates PV-resident proteins, several of which are essential for the formation of a functional intravacuolar network. Moreover, we show that WNG1-dependent phosphorylation of these proteins is required for their membrane association, and thus their ability to tubulate membranes. Consequently, WNG1 knockout parasites have an aberrant PV membrane ultrastructure. Collectively, our results describe a unique family of Toxoplasma kinases and implicate phosphorylation of secreted proteins as a mechanism of regulating PV formation during parasite infection.

cell biology↗

bioRxiv2018

Phosphorylation of a Toxoplasma gondii tyrosine transporter by calcium-dependent kinase 3 is important for parasite fitness

Toxoplasma gondii parasites rapidly exit their host cell when exposed to calcium ionophores. The calcium-dependent protein kinase 3 (TgCDPK3) was previously identified as a key mediator in this process, as TgCDPK3 knockout ({Delta}cdpk3) parasites fail to egress in a timely manner. Phosphoproteomic analysis comparing WT with {Delta}cdpk3 parasites revealed changes in the TgCDPK3-dependent phosphoproteome that included proteins important for regulating motility, but also metabolic enzymes, indicating that TgCDPK3 controls processes beyond egress. Here we have investigated a predicted direct target of TgCDPK3, a putative transporter of the major facilitator superfamily (MFS) and show that it is rapidly phosphorylated after induction of calcium signalling. Conditional knockout (KO) of the transporter reveals an essential role in the lytic cycle during intracellular growth with a transcriptome signature of amino acid-starved parasites. Using a combination of metabolomics and heterologous expression, we confirmed a primary role in tyrosine import. Complementation with phosphorylation site mutants shows that phosphorylation of serine 56 (S56) by TgCDPK3 gives the parasites a growth benefit in competition assays. Collectively, these findings validate an important, albeit non-essential role for TgCDPK3 in the regulation of metabolic processes, in addition to motility.\n\nAuthor summaryToxoplasma gondii is an obligate intracellular parasite. To survive and spread throughout the host it must repeatedly infect, replicate within and exit, host cells. These recurring cycles of infection and egress rely on signalling pathways that allow the parasites to sense and respond rapidly to their environment. While some key kinases and secondary messengers within these pathways have been identified, functional analysis of non-kinases has been very limited. This is especially true for candidates that are not predicted to play a role in active motility or are not known to function in established signalling pathways. Here we have followed up on an unexpected target of the T. gondii calcium-dependent kinase 3 (TgCDPK3), a plant-like calcium dependent kinase, that was previously shown to play an important role in calcium-mediated exit from the host cell. We show that, in addition to controlling motility of the parasite (as previously shown), TgCDPK3 phosphorylates an essential tyrosine transporter in the plasma membrane. Mutational analysis of the phosphorylation sites demonstrates an important role in maintaining parasite fitness, thus demonstrating that TgCDPK3 plays a pleiotropic role in controlling both egress and metabolism.

microbiology↗