Biology subjects

Lourido, S.

Publications and source records attributed to Lourido, S..

25 records · Page 2Linked to original sources

bioRxiv2021

High-throughput functionalization of the Toxoplasma kinome uncovers a novel regulator of invasion and egress

Protein kinases regulate fundamental aspects of cell biology in all eukaryotes, making them attractive chemotherapeutic targets in Apicomplexan parasites such as the causative agents of malaria (Plasmodium spp.) and toxoplasmosis (Toxoplasma gondii). However, the precise roles of individual parasite kinases cannot be inferred simply from sequence identity, due to rewiring of signaling pathways and the shifting repertoire of kinases across species. To systematically examine the parasite kinome, we developed a high-throughput (HiT) CRISPR-mediated tagging strategy to endogenously label all predicted cytosolic protein kinases with a synthetic sequence encoding the minimal auxin-inducible degron (mAID) linked to a fluorophore and epitope tag. The system enables the assembly of thousands of tagging vectors from synthetic sequences in a single reaction and the pooled generation of mutants to examine kinase localization and function. We examined the phenotypes associated with kinase knock-down in 1,160 arrayed clones by replica-plating in the presence or absence of auxin and found broad defects across the lytic cycle for 109 clonal isolates, assigning localizations to 39 proteins, and associating 15 kinases within 6 distinct morphological phenotypes. The relative fitness of tagged alleles was also examined by tracking the relative abundance of individual guide RNAs as parasite populations progressed through the lytic cycle, in the presence or absence of auxin. Pooled screening had a high predictive value and differentiated between delayed and acute death. Demonstrating the value of this resource, we identified a novel kinase associated with delayed death as a novel regulator of invasion and egress. We call the previously unstudied kinase Store Potentiating/Activating Regulatory Kinase (SPARK), based on its impact on intracellular Ca2+ stores at key moments during the lytic cycle. Despite having a similar kinase domain to the mammalian PDK1, SPARK lacks the canonical lipid-binding domain and we find no indication SPARK positively regulates other AGC kinases, suggesting a rewiring of signaling pathways to accommodate parasite adaptations. The HiT vector screening system extends the applications of genome-wide screens into complex cellular phenotypes, providing a scalable and versatile platform for the dissection of apicomplexan cell biology.

microbiology↗

bioRxiv2021

Toxoplasma gondii subverts the host ESCRT machinery for parasite uptake of host cytosolic proteins

Toxoplasma gondii is a master manipulator capable of effectively siphoning the resources from the host cell for its intracellular subsistence. However, the molecular underpinnings of how the parasite gains resources from its host remain largely unknown. Residing within a non-fusogenic parasitophorous vacuole, the parasite must acquire resources across the limiting membrane of its replicative niche, which is decorated with parasite proteins including those secreted from dense granules. We discovered a role for the Endosomal Sorting Complex Required for Transport (ESCRT) machinery in host cytosolic protein uptake by T. gondii by disrupting host ESCRT function. We identified the transmembrane dense granule protein TgGRA14, which contains motifs homologous to the late domain motifs of HIV-1 Gag, as a candidate for the recruitment of the host ESCRT machinery to the PV membrane. Using an HIV virus-like particle (VLP) release assay, we found that the motif-containing portion of TgGRA14 is sufficient to substitute for HIV Gag late domain to mediate ESCRT-dependent VLP budding. We also show that TgGRA14 is proximal to and interacts with host ESCRT components and other dense granule proteins during infection. Furthermore, analysis of GRA14-deficient parasites revealed a marked reduction in ingestion of a host cytosolic protein compared to WT parasites. Thus, we propose a model in which T. gondii recruits the host ESCRT machinery to the PV where it can interact with TgGRA14 for the internalization of host cytosolic proteins across the PVM. These findings provide new insight into how T. gondii accesses contents of the host cytosol by exploiting a key pathway for vesicular budding and membrane scission. Author summaryIntracellular pathogens exploit their host to gain the resources necessary to sustain infection; however, precisely how the intracellular parasite Toxoplasma gondii acquires essential nutrients from its host remains poorly understood. Previous work showed that T. gondii is capable of internalizing host derived cytosolic proteins and delivering them to its lysosome-like compartment for degradation. However, the mechanism by which the material is trafficked across the membrane delimiting the replicative vacuole in which the parasite resides remained unclear. Here, we report a role for the parasite effector protein TgGRA14 in the recruitment of the host ESCRT machinery for the uptake of host cytosolic proteins. Important human pathogens have developed strategies for exploiting the host ESCRT machinery for intracellular subsistence. Our study sheds lights on the strategy used by a eukaryotic pathogen in subverting the host ESCRT machinery for the internalization of resources from its host cells.

microbiology↗

bioRxiv2020

A PEROXO-Tag enables rapid isolation of peroxisomes from human cells

Peroxisomes are metabolic organelles that perform a diverse array of critical functions in human physiology. Traditional isolation methods for peroxisomes can take more than one hour to complete and can be laborious to implement. To address this, we have now extended our prior work on rapid organellar isolation to peroxisomes via the development of a peroxisomally-localized 3XHA epitope tag ("PEROXO-Tag") and associated immunoprecipitation ("PEROXO-IP") workflow. Our PEROXO-IP workflow has excellent reproducibility, is easy to implement, and achieves highly rapid (~10 minutes post-homogenization) and specific isolation of human peroxisomes, which we characterize here via proteomic profiling. By offering speed, specificity, reproducibility, and ease of use, the PEROXO-IP workflow should facilitate studies on the biology of peroxisomes.

cell biology↗

bioRxiv2019

A genome-wide loss-of-function screen identifies Toxoplasma gondii genes that determine fitness in interferon gamma-activated murine macrophages

Macrophages play an essential role in the early immune response against Toxoplasma and are the cell type preferentially infected by the parasite in vivo. Interferon gamma (IFN{gamma}) elicits a variety of anti-Toxoplasma activities in macrophages. Using a genome-wide CRISPR screen we identified [~]130 Toxoplasma genes that determine parasite fitness in naive macrophages and [~]466 genes that determine fitness in IFN{gamma}-stimulated murine macrophages, seven of which we investigated and confirmed. We show that one of these genes encodes dense granule protein GRA45, which contains a putative chaperone-like domain, and which we show is critical in preventing other GRA effectors from aggregating. Parasites lacking GRA45 mislocalize GRA effectors upon secretion, are more susceptible to IFN{gamma}-mediated growth inhibition, and have reduced virulence in mice. Our results provide a resource for the community to further explore the function of Toxoplasma genes that determine fitness in IFN{gamma}-stimulated macrophages. IMPORTANCEThe intracellular parasite Toxoplasma gondii can cause congenital infections and severe disease in immunocompromised patients. The cytokine IFN{gamma} can block parasite replication by upregulating a variety of toxoplasmacidal mechanisms in many cells, including macrophages. Toxoplasma preferentially infects macrophages. Therefore, the parasite has evolved mechanisms to survive in these cells in the presence of IFN{gamma}. Here, we generated pools of Toxoplasma mutants for every gene and determined which mutants were specifically depleted in IFN{gamma}-stimulated macrophages, thus identifying parasite genes determining fitness in these cells. We show that one of these genes encodes for a dense granule protein (GRA45) that plays an important role in preventing other GRA effectors from aggregating. Parasites without GRA45 mislocalize GRA effectors upon secretion, have enhanced susceptibility to IFN{gamma}-mediated growth inhibition, and are avirulent in mice. Thus, our screen provides a resource to the Toxoplasma community to determine the function of Toxoplasma genes that affect its fitness in IFN{gamma}-stimulated macrophages.

microbiology↗

bioRxiv2019

Genetic screens reveal a central role for heme biosynthesis in artemisinin susceptibility

Artemisinins have revolutionized the treatment of Plasmodium falciparum malaria, however, resistance threatens to undermine global control efforts. To explore artemisinin resistance in apicomplexan parasites broadly, we used genome-scale CRISPR screens recently developed for Toxoplasma gondii to discover sensitizing and desensitizing mutations. Using a sublethal concentration of dihydroartemisinin (DHA), we uncovered the putative porphyrin transporter Tmem14c whose disruption increases DHA susceptibility. Screens performed under high doses of DHA provided evidence that mitochondrial metabolism can modulate resistance. We show that disruption of a top candidate from the screens, the mitochondrial protease DegP2, lowered levels of free heme and decreased DHA susceptibility, without significantly altering fitness in culture. Deletion of the homologous gene in P. falciparum, PfDegP, similarly lowered heme levels and DHA susceptibility. These results expose the vulnerability of the heme biosynthetic pathway for genetic perturbations that can lead to survival in the presence of DHA. We go on to show that chemically reducing heme biosynthesis can decrease the sensitivity of both T. gondii and P. falciparum to DHA, suggesting guidelines for developing combination therapies.

microbiology↗

bioRxiv2019

Identification of a master regulator of differentiation in Toxoplasma

Toxoplasma gondii chronically infects a quarter of the worlds population, and its recrudescence can cause life-threatening disease in immunocompromised individuals and recurrent ocular lesions in the immunocompetent. Chronic stages are established by differentiation of rapidly replicating tachyzoites into slow-growing bradyzoites, which form intracellular cysts resistant to immune clearance and existing therapies. Despite its central role in infection, the molecular basis of chronic differentiation is not understood. Through Cas9-mediated genetic screening and single-cell transcriptional profiling, we identify and characterize a putative transcription factor (BFD1) as necessary and sufficient for differentiation. Translation of BFD1 appears to be stress regulated, and its constitutive expression elicits differentiation in the absence of stress. As a Myb-like factor, BFD1 provides a counterpoint to the ApiAP2 factors which dominate our current view of parasite gene regulation. Overall, BFD1 provides a genetic switch to study and control Toxoplasma differentiation, and will inform prevention and treatment of chronic infection.

microbiology↗

bioRxiv2018

Identification of cryptic stator subunits from an apicomplexan ATP synthase

The mitochondrial ATP synthase is a macromolecular motor that uses the proton gradient to generate ATP. Proper ATP synthase function requires a stator linking the catalytic and rotary portions of the complex. However, sequence-based searches fail to identify genes encoding stator subunits in apicomplexan parasites like Toxoplasma gondii or the related organisms that cause malaria. Here, we identify 11 previously unknown subunits from the Toxoplasma ATP synthase, which lack homologs outside the phylum. Hidden Markov modeling suggests that two of them--ICAP2 and ICAP18--share distant homology with mammalian stator subunits. Our analysis shows that both proteins form part of the ATP synthase complex. Depletion of ICAP2 leads to aberrant mitochondrial morphology, decreased oxygen consumption, and disassembly of the complex, consistent with its role as an essential component of the Toxoplasma ATP synthase. Our findings highlight divergent features of the central metabolic machinery in apicomplexans, which may reveal new therapeutic opportunities.

microbiology↗