Biology subjects

Cobb, D. W.

Publications and source records attributed to Cobb, D. W..

6 recordsLinked to original sources

bioRxiv2023

In situ cryoET reveals inhibitor-induced perturbations in Pf80S GTPase interactions

Malaria parasites rely heavily on rapid, high fidelity protein synthesis to infect and replicate in human erythrocytes, making translation an attractive target for new antimalarials. Here, we have determined in situ structures of Pf80S ribosomes in thirteen conformational and compositional states from cryoFIB-milled Plasmodium falciparum-infected human erythrocytes across the stages of asexual intraerythrocytic parasite replication. We observe eight active translation intermediates, enabling us to define the native malarial translation elongation cycle, which surprisingly features a bifurcation at the decoding stage of the cycle that has not previously been described. Examination of perturbations in the distribution of ribosomes among these states in the presence of a malaria-specific translation inhibitor suggests that the inhibitor impedes PfeEF2 and PfeEF1 interactions with the ribosome. We integrated our in situ cryoET data with proteomic and ultrastructural data to arrive at a deeper understanding of malarial translation, which will inform development of new therapies.

biophysics↗

bioRxiv2022

RAPID, TIME-RESOLVED PROXIMITY LABELING BY SBP1 IDENTIFIES A PORIN DOMAIN PROTEIN AT THE MALARIA PARASITE PERIPHERY

The deadly human malaria-causing parasite, Plasmodium falciparum relies on its capacity to completely remodel its host red blood cell (RBC) through the export of hundreds of parasite proteins across several membranes to the RBC. Among these exported proteins are numerous membrane proteins that are inserted into the parasite plasma membrane (PPM) during their transport via the secretory pathway. It is not known how these exported membrane proteins are extracted from the PPM for export. To answer this question, we fused the exported membrane protein skeleton binding protein 1 (SBP1) with the rapid, efficient, and promiscuous biotin ligase known as TurboID (SBP1TbID). Our data show that the SBP1TbID fusion protein was exported efficiently to the host RBC and was able to rapidly biotinylate proteins at the host-parasite interface during its export as well as at its final destination in the host RBC. Using time-resolved proximity biotinylation and label-free quantitative proteomics, we identified early (pre-export) interactors and late (post-export) interactors of SBP1TbID. This led to the identification of 24 proteins that were 10-fold or more enriched in the pre-export time point compared to the post-export time point. Among these early interactors were two promising membrane-associated proteins, one of which has a predicted porin domain, that could potentially act as a translocon at the PPM for exported membrane proteins (Plasmodium translocon of exported membrane proteins or PTEM). Both proteins localize to the host-parasite interface during early stages of the intraerythrocytic cycle and conditional knockdown of these candidates show that they play essential roles in the asexual lifecycle of the parasite. Taken together, our data suggest that these two proteins may play a role in extracting membrane proteins from the PPM for export to the host RBC.

cell biology↗

bioRxiv2020

A druggable oxidative folding pathway in the endoplasmic reticulum of human malaria parasites

Malaria remains a major global health problem, and there exists a constant need to identify druggable weaknesses in P. falciparum biology. The endoplasmic reticulum (ER) has many essential roles in the asexual lifecycle and may offer new drug targets, but it remains critically understudied. We generated conditional mutants of the putative redox-active, ER chaperone PfJ2, and show that it is essential for parasite survival. Using a redox-active cysteine crosslinker, we identify its substrates to be other mediators of oxidative folding, PfPDI8 and PfPDI11, suggesting a redox-regulatory role for PfJ2. Knockdown of these protein disulfide isomerases in PfJ2 conditional mutants show that PfPDI11 is not essential, while PfPDI8 is essential for asexual growth and may work in a complex with PfJ2 and other ER chaperones. Finally, we show that these redox interactions in the parasite ER are sensitive to small molecule inhibition. Together these data build a model for how oxidative folding occurs in the P. falciparum ER and demonstrate its suitability for antimalarial drug development.

microbiology↗

bioRxiv2018

The ER chaperone PfGRP170 is essential for asexual development and is linked to stress response in malaria parasites.

The vast majority of malaria mortality is attributed to one parasite species: Plasmodium falciparum. Asexual replication of the parasite within the red blood cell is responsible for the pathology of the disease. In Plasmodium, the endoplasmic reticulum (ER) is a central hub for protein folding and trafficking as well as stress response pathways. In this study, we tested the role of an uncharacterized ER protein, PfGRP170, in regulating these key functions by generating conditional mutants. Our data show that PfGRP170 localizes to the ER and is essential for asexual growth, specifically required for proper development of schizonts. PfGRP170 is essential for surviving heat shock, suggesting a critical role in cellular stress response. The data demonstrate that PfGRP170 interacts with the Plasmodium orthologue of the ER chaperone, BiP. Finally, we found that loss of PfGRP170 function leads to the activation of the Plasmodium eIF2 kinase, PK4, suggesting a specific role for this protein in this parasite stress response pathway.

cell biology↗

bioRxiv2018

CRISPR/Cas9 gene editing to make conditional mutants of the human malaria parasite Plasmodium falciparum

Malaria is a significant cause of morbidity and mortality worldwide. This disease, which primarily affects those living in tropical and subtropical regions, is caused by infection with Plasmodium parasites. The development of better drugs to combat malaria can be accelerated by improving our understanding of the biology of this complex parasite. Genetic manipulation of these parasites is key to understanding their biology, but historically, the genome of P. falciparum has been difficult to manipulate. Recently, CRISPR/Cas9 genome editing has been utilized in malaria parasites, allowing for easier protein tagging, generation of conditional protein knockdowns, and deletion of genes. CRISPR/Cas9 genome editing has proven to be a powerful tool for advancing the field of malaria research. Here, we describe a CRISPR/Cas9 method for generating glmS-based conditional knockdown mutants in P. falciparum. The method is highly adaptable to other types of genetic manipulations, including protein tagging and gene knockouts.

cell biology↗

bioRxiv2017

The exported chaperone PfHsp70x is dispensable for the Plasmodium falciparum intraerythrocytic lifecycle

Export of parasite proteins into the host erythrocyte is essential for survival of Plasmodium falciparum during its asexual lifecycle. While several studies described key factors within the parasite that are involved in protein export, the mechanisms employed to traffic exported proteins within the host cell are currently unknown. Members of the Hsp70 family of chaperones, together with their Hsp40 co-chaperones, facilitate protein trafficking in other organisms, and are thus likely used by P. falciparum in the trafficking of its exported proteins. A large group of Hsp40 proteins is encoded by the parasite and exported to the host cell, but only one Hsp70, PfHsp70x, is exported with them.\n\nPfHsp70x is absent from most Plasmodium species and is found only in P. falciparum and closely-related species that infect Apes. Herein, we have utilized CRISPR/Cas9 genome editing in P. falciparum to investigate the essentiality of PfHsp70x. We show that parasitic growth was unaffected by knockdown of PfHsp70x using both the DHFR-based Destabilization Domain and the glmS ribozyme system. Similarly, a complete gene knockout of PfHsp70x did not affect the ability of P. falciparum to proceed through its intraerythrocytic lifecycle. The effect of PfHsp70x knockdown/knockout on the export of proteins to the host RBC, including the critical virulence factor PfEMP1, was tested and we found that this process was unaffected. These data show that although PfHsp70x is the sole exported Hsp70, it is not essential for the asexual development of P. falciparum.\n\nImportanceHalf of the worlds population lives at risk for malaria. The intraerythrocytic lifecycle of Plasmodium spp. is responsible for clinical manifestations of malaria; therefore, knowledge of the parasites ability to survive within the erythrocyte is needed to combat the deadliest agent of malaria, P. falciparum. An outstanding question in the field is how P. falciparum undertakes the essential process of trafficking its proteins within the host cell. In most organisms, chaperones such as Hsp70 are employed in protein trafficking. Of the human-disease causing Plasmodium species, the chaperone PfHsp70x is unique to P. falciparum, and it is the only parasite protein of its kind exported to the host (1). This has placed PfHsp70x as an ideal target to inhibit protein trafficking and kill the parasite. However, we show that PfHsp70x is not required for export of parasite effectors nor is it essential for parasite survival inside of the RBC.

microbiology↗