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Author Spotlight: Identifying Compensatory Pathways in Malaria Parasites Containing Hypomorphic Allele of Essential Protein Kinases
Published on: November 22, 2024
Complex nutrient channel phenotypes despite Mendelian inheritance in a Plasmodium falciparum genetic cross
Ankit Gupta1, Abdullah A B Bokhari1, Ajay D Pillai1
1Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America.
Abstract:
Malaria parasites activate a broad-selectivity ion channel on their host erythrocyte membrane to obtain essential nutrients from the bloodstream. This conserved channel, known as the plasmodial surface anion channel (PSAC), has been linked to parasite clag3 genes in P. falciparum, but epigenetic switching between the two copies of this gene hinders clear understanding of how the encoded protein determines PSAC activity. Here, we used linkage analysis in a P. falciparum cross where one parent carries a single clag3 gene to overcome the effects of switching and confirm a primary role of the clag3 product with high confidence. Despite Mendelian inheritance, CLAG3 conditional knockdown revealed remarkably preserved nutrient and solute uptake. Even more surprisingly, transport remained sensitive to a CLAG3 isoform-specific inhibitor despite quantitative knockdown, indicating that low doses of the CLAG3 transgene are sufficient to confer block. We then produced a complete CLAG3 knockout line and found it exhibits an incomplete loss of transport activity, in contrast to rhoph2 and rhoph3, two PSAC-associated genes that cannot be disrupted because nutrient uptake is abolished in their absence. Although the CLAG3 knockout did not incur a fitness cost under standard nutrient-rich culture conditions, this parasite could not be propagated in a modified medium that more closely resembles human plasma. These studies implicate oligomerization of CLAG paralogs encoded by various chromosomes in channel formation. They also reveal that CLAG3 is dispensable under standard in vitro conditions but required for propagation under physiological conditions.
Insights
Malaria parasites use the plasmodial surface anion channel (PSAC) for nutrient uptake. CLAG3 is essential for PSAC function, particularly under physiological conditions, despite dispensability in standard lab cultures.
Area of Science:
- Parasitology
- Molecular Biology
- Membrane Transport
Background:
- Malaria parasites rely on the plasmodial surface anion channel (PSAC) for nutrient acquisition from host erythrocytes.
- The CLAG3 gene family in *P. falciparum* is linked to PSAC activity, but epigenetic switching complicates understanding its precise role.
- Previous studies faced challenges in elucidating CLAG3's function due to gene duplication and switching.
Purpose of the Study:
- To definitively establish the role of CLAG3 in PSAC activity and nutrient transport in *P. falciparum*.
- To investigate the functional significance of CLAG3 under varying physiological conditions.
- To explore the potential for CLAG3 paralog interactions in channel formation.
Main Methods:
- Utilized linkage analysis in a *P. falciparum* cross with a single *clag3* gene parent to circumvent switching effects.
- Performed conditional knockdown and complete knockout of the *CLAG3* gene.
- Assessed nutrient and solute uptake using transport assays.
- Evaluated parasite fitness in standard and modified (physiological) culture media.
- Compared *CLAG3* knockout phenotypes with those of *rhoph2* and *rhoph3* mutants.
Main Results:
- Confirmed a primary role for CLAG3 in PSAC activity via Mendelian inheritance studies.
- Conditional CLAG3 knockdown showed preserved nutrient uptake, with transport remaining sensitive to inhibitors.
- Complete CLAG3 knockout resulted in incomplete loss of transport, unlike essential *rhoph2* and *rhoph3* genes.
- CLAG3 knockout parasites showed no fitness cost in nutrient-rich media but failed to propagate in a plasma-mimicking medium.
Conclusions:
- CLAG3 is crucial for PSAC-mediated transport, especially under physiological conditions mimicking human plasma.
- Oligomerization of CLAG paralogs likely contributes to PSAC channel formation.
- CLAG3 is dispensable for *P. falciparum* growth in vitro but essential for survival under conditions closer to the host environment.
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