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Multidrug-resistant Plasmodium falciparum parasites have emerged in Cambodia and neighboring countries in Southeast Asia, compromising the efficacy of first-line antimalarial combinations. Dihydroartemisinin + piperaquine (PPQ) treatment failure rates have risen to as high as 50% in some areas in this region. For PPQ, resistance is driven primarily by a series of mutant alleles of the P . falciparum chloroquine resistance transporter (PfCRT). PPQ resistance was reported in China three decades earlier, but the molecular driver remained unknown. Herein, we identify a PPQ-resistant pfcrt allele (China C) from Yunnan Province, China, whose genotypic lineage is distinct from the PPQ-resistant pfcrt alleles currently observed in Cambodia. Combining gene editing and competitive growth assays, we report that PfCRT China C confers moderate PPQ resistance while re-sensitizing parasites to chloroquine (CQ) and incurring a fitness cost that manifests as a reduced rate of parasite growth. PPQ transport assays using purified PfCRT isoforms, combined with molecular dynamics simulations, highlight differences in drug transport kinetics and in this transporter’s central cavity conformation between China C and the current Southeast Asian PPQ-resistant isoforms. We also report a novel computational model that incorporates empirically determined fitness landscapes at varying drug concentrations, combined with antimalarial susceptibility profiles, mutation rates, and drug pharmacokinetics. Our simulations with PPQ-resistant or -sensitive parasite lines predict that a three-day regimen of PPQ combined with CQ can effectively clear infections and prevent the evolution of PfCRT variants. This work suggests that including CQ in combination therapies could be effective in suppressing the evolution of PfCRT-mediated multidrug resistance in regions where PPQ has lost efficacy.

Pendrin (SLC26A4) is an anion exchanger that mediates bicarbonate (HCO 3 − ) exchange for chloride (Cl − ) and is crucial for maintaining pH and salt homeostasis in the kidney, lung, and cochlea. Pendrin also exports iodide (I − ) in the thyroid gland. Pendrin mutations in humans lead to Pendred syndrome, causing hearing loss and goiter. Inhibition of pendrin is a validated approach for attenuating airway hyperresponsiveness in asthma and for treating hypertension. However, the mechanism of anion exchange and its inhibition by drugs remains poorly understood. We applied cryo-electron microscopy to determine structures of pendrin from Sus scrofa in the presence of either Cl − , I − , HCO 3 − or in the apo-state. The structures reveal two anion-binding sites in each protomer, and functional analyses show both sites are involved in anion exchange. The structures also show interactions between the Sulfate Transporter and Anti-Sigma factor antagonist (STAS) and transmembrane domains, and mutational studies suggest a regulatory role. We also determine the structure of pendrin in a complex with niflumic acid (NFA), which uncovers a mechanism of inhibition by competing with anion binding and impeding the structural changes necessary for anion exchange. These results reveal directions for understanding the mechanisms of anion selectivity and exchange and their regulations by the STAS domain. This work also establishes a foundation for analyzing the pathophysiology of mutations associated with Pendred syndrome. Here the authors report structures of pendrin, an anion exchanger, in complex with its substrate Cl − , I − , or HCO 3 − , which reveal two anion binding sites in each protomer. The authors also identify binding sites of a pendrin inhibitor, niflumic acid.

Anion Exchanger 1 (AE1) is an elevator-type transporter that plays a key role in acid-base homeostasis of erythrocytes. Here, we report three high-resolution cryo-electron microscopy (cryo-EM) structures of distinct states of AE1: two inward-facing (IF1 and IF2) and one outward-facing (OF). Uptake assay revealed the modulatory effect of phosphatidylinositol 4,5-bisphosphate (PIP 2 ) lipids on AE1. Molecular dynamics simulations are conducted on these structures to determine the anion binding sites in AE1. We then use advanced enhanced sampling to study the OF⇌IF transition in AE1 in three systems: apo , HCO 3 – -bound, and an AE1 system in which cryo-EM-determined PIP 2 lipids had been removed. The transition pathways were then used to calculate the free energy of the OF⇌IF transition in AE1 under different conditions. The results show how substrate reduces the transition barrier against transport. Furthermore, they capture the inhibitory effect of PIP 2 lipids and provide a molecular mechanism for this inhibitory effect. AE1 is the most abundant membrane protein in erythrocytes. Here, authors report cryo-EM structures in multiple states and demonstrate the inhibitory effect of PIP2 lipids. Free energy calculations reveal the molecular mechanism for PIP 2 inhibition.

Enzymes undergo dynamic conformational changes during catalysis, yet conventional high-resolution structural methods typically capture only the most stable states. Here, we address this gap using rapid UV photolysis of a chemically caged substrate with cryogenic time-resolved electron microscopy (cryo-TREM). We elucidate the catalytic mechanism of GtrB, a membrane-bound glycosyltransferase that transfers glucose from UDP-glucose to the lipid carrier undecaprenyl phosphate. We visualized how GtrB, which has an active site ~15 Å from the membrane, transitions during the catalytic cycle to move each substrate in proximity for catalysis. From a single dataset, we resolved distinct conformational states: the initial substrate-bound state, a catalytically poised intermediate, and the product-bound state. Through molecular dynamics simulations and biochemical analyses, we identify coordinated movements within the active site that drive catalysis. These findings provide a molecular framework for understanding how glycosyltransferases function and highlight a broadly applicable strategy for capturing dynamic enzymatic states in native-like environments. Here the authors applied cryogenic time-resolved electron microscopy with rapid UV photolysis of a caged substrate to elucidate the catalytic mechanism of lipid-sugar transfer within the bacterial membrane by the glycosyltransferase GtrB.

Artemisinin-based combination therapy (ACT) is the mainstay of effective treatment of Plasmodium falciparum malaria. However, the long-term utility of ACTs is imperiled by widespread partial artemisinin resistance in Southeast Asia and its recent emergence in parts of East Africa. This underscores the need to identify chemotypes with new modes of action (MoAs) to circumvent resistance to ACTs. In this study, we characterized the asexual blood stage antiplasmodial activity and resistance mechanisms of LDT-623, a 4-aminoquinoline (4-AQ). We also detected LDT-623 activity against multiple stages (liver schizonts, stage IV-V gametocytes, and ookinetes) of Plasmodium ’s life cycle, a feature unlike other 4-AQs such as chloroquine (CQ) and piperaquine (PPQ). Using heme fractionation profiling and drug uptake studies in PfCRT-containing proteoliposomes, we observed inhibition of hemozoin formation and PfCRT-mediated transport, which constitute characteristic features of 4-AQs’ MoA. We also found minimal cross-resistance to LDT-623 in a panel of mutant pfcrt or pfmdr1 lines, but not the PfCRT F145I mutant that is highly resistant to PPQ resistance yet is very unfit. No P. falciparum parasites were recovered in an in vitro resistance selection study, suggesting a high barrier for resistance to emerge. Finally, a competitive growth assay comprising >50 barcoded parasite lines with mutated resistance mediators or major drug targets found no evidence of cross-resistance. Our findings support further exploration of this promising 4-AQ.

The brain depends on glucose as a source of energy. This implies the presence of glucose transporters, being GLUT1 and GLUT3 the most relevant. Expression of GLUT12 is found in mouse and human brain at low levels. We previously demonstrated GLUT12 upregulation in the frontal cortex of aged subjects that was even higher in aged Alzheimer’s disease (AD) patients. However, the cause and the mechanism through which this increase occurs are still unknown. Here, we aimed to investigate whether the upregulation of GLUT12 in AD is related with aging or Aβ deposition in comparison with GLUT1, GLUT3, and GLUT4. In the frontal cortex of two amyloidogenic mouse models (Tg2576 and APP/PS1) GLUT12 levels were increased. Contrary, expression of GLUT1 and GLUT3 were decreased, while GLUT4 did not change. In aged mice and the senescence-accelerated model SAMP8, GLUT12 and GLUT4 were upregulated in comparison with young animals. GLUT1 and GLUT3 did not show significant changes with age. The effect of β-amyloid (Aβ) deposition was also evaluated in Aβ peptide i.c.v. injected mice. In the hippocampus, GLUT12 expression increased whereas GLUT4 was not modified. Consistent with the results in the amyloidogenic models, GLUT3 and GLUT1 were downregulated. In summary, Aβ increases GLUT12 protein expression in the brain pointing out a central role of the transporter in AD pathology and opening new perspectives for the treatment of this neurodegenerative disease.

Malaria elimination efforts in Southeast Asia have been hindered by multidrug-resistant Plasmodium falciparum . High-grade resistance to piperaquine (PPQ, used in combination with dihydroartemisinin) is associated with PfCRT mutations that arose in strains expressing the PfCRT Dd2 isoform, which mediates resistance to the related 4-aminoquinoline chloroquine (CQ). The PPQ-resistant PfCRT haplotype Dd2 + F145I mediates the highest level resistance but causes a significant growth defect in intra-erythrocytic parasites. Recently, three separate mutations (F131C, I347T and C258W) have been observed on Dd2 + F145I PfCRT either during extended parasite culture or in Southeast Asian isolates no longer subject to PPQ pressure. Competitive growth assays with pfcrt -edited parasites reveal that these compensatory mutations reduce the fitness defect caused by F145I. PPQ survival assays on edited lines show a loss of PPQ resistance in two of the three variants, including the field mutant (C258W). The latter restores CQ resistance. None of these variants alter parasite susceptibility to the first-line partner drug, mefloquine. Utilizing drug transport assays with purified PfCRT isoforms reconstituted into proteoliposomes, we identify differences in mutant PfCRT-mediated transport of PPQ and CQ. Molecular dynamics energy minimization calculations predict that these same mutations cause small but significant conformational changes in PfCRT regions implicated in drug interactions. Metabolomic analyses of isogenic parasite lines reveal differences in hemoglobin-derived peptide accumulation as a hallmark of PfCRT variation. These studies highlight the transient nature of PPQ resistance upon removal of drug pressure and suggest a strategy for employing this drug as part of multiple first-line therapies. Our study leverages gene editing techniques in Plasmodium falciparum asexual blood stage parasites to profile novel mutations in mutant PfCRT, an important mediator of piperaquine resistance, which developed in Southeast Asian field isolates or in parasites cultured for long periods of time. We provide evidence that increased parasite fitness of these lines is the primary driver for the emergence of these PfCRT variants. These mutations differentially impact parasite susceptibility to piperaquine and chloroquine, highlighting the multifaceted effects of single point mutations in this transporter. Molecular features of drug resistance and parasite physiology were examined in depth using proteoliposome-based drug uptake studies and peptidomics, respectively. Energy minimization calculations, showing how these novel mutations might impact the PfCRT structure, suggested a small but significant effect on drug interactions. This study reveals the subtle interplay between antimalarial resistance, parasite fitness, PfCRT structure, and intracellular peptide availability in PfCRT-mediated parasite responses to changing drug selective pressures.

Choline is an essential nutrient that the human body needs in vast quantities for cell membrane synthesis, epigenetic modification and neurotransmission. The brain has a particularly high demand for choline, but how it enters the brain remains unknown 1 – 3 . The major facilitator superfamily transporter FLVCR1 (also known as MFSD7B or SLC49A1) was recently determined to be a choline transporter but is not highly expressed at the blood–brain barrier, whereas the related protein FLVCR2 (also known as MFSD7C or SLC49A2) is expressed in endothelial cells at the blood–brain barrier 4 – 7 . Previous studies have shown that mutations in human Flvcr2 cause cerebral vascular abnormalities, hydrocephalus and embryonic lethality, but the physiological role of FLVCR2 is unknown 4 , 5 . Here we demonstrate both in vivo and in vitro that FLVCR2 is a BBB choline transporter and is responsible for the majority of choline uptake into the brain. We also determine the structures of choline-bound FLVCR2 in both inward-facing and outward-facing states using cryo-electron microscopy. These results reveal how the brain obtains choline and provide molecular-level insights into how FLVCR2 binds choline in an aromatic cage and mediates its uptake. Our work could provide a novel framework for the targeted delivery of therapeutic agents into the brain. FLVCR2 is expressed in the blood–brain barrier of mouse and human, and is the major mediator of choline uptake into the brain.

Obesity constitutes a global health epidemic which worsens the main leading death causes such as type 2 diabetes, cardiovascular diseases, and cancer. Changes in the metabolism in patients with obesity frequently lead to insulin resistance, along with hyperglycemia, dyslipidemia and low-grade inflammation, favoring a more aggressive tumor microenvironment. One of the hallmarks of cancer is the reprogramming of the energy metabolism, in which tumor cells change oxidative phosphorylation to aerobic glycolysis or “Warburg effect”. Aerobic glycolysis is faster than oxidative phosphorylation, but less efficient in terms of ATP production. To obtain sufficient ATP, tumor cells increase glucose uptake by the glucose transporters of the GLUT/SLC2 family. The human glucose transporter GLUT12 was isolated from the breast cancer cell line MCF7. It is expressed in adipose tissue, skeletal muscle and small intestine, where insulin promotes its translocation to the plasma membrane. Moreover, GLUT12 over‐expression in mice increases the whole‐body insulin sensitivity. Thus, GLUT12 has been proposed as a second insulin‐responsive glucose transporter. In obesity, GLUT12 is downregulated and does not respond to insulin. In contrast, GLUT12 is overexpressed in human solid tumors such as breast, prostate, gastric, liver and colon. High glucose concentration, insulin, and hypoxia upregulate GLUT12 both in adipocytes and tumor cells. Inhibition of GLUT12 mediated Warburg effect suppresses proliferation, migration, and invasion of cancer cells and xenografted tumors. This review summarizes the up-to-date information about GLUT12 physiological role and its implication in obesity and cancer, opening new perspectives to consider this transporter as a therapeutic target.

Obesity constitutes a global health epidemic which worsens the main leading death causes such as type 2 diabetes, cardiovascular diseases, and cancer. Changes in the metabolism in patients with obesity frequently lead to insulin resistance, along with hyperglycemia, dyslipidemia and low-grade inflammation, favoring a more aggressive tumor microenvironment. One of the hallmarks of cancer is the reprogramming of the energy metabolism, in which tumor cells change oxidative phosphorylation to aerobic glycolysis or “Warburg effect”. Aerobic glycolysis is faster than oxidative phosphorylation, but less efficient in terms of ATP production. To obtain sufficient ATP, tumor cells increase glucose uptake by the glucose transporters of the GLUT/SLC2 family. The human glucose transporter GLUT12 was isolated from the breast cancer cell line MCF7. It is expressed in adipose tissue, skeletal muscle and small intestine, where insulin promotes its translocation to the plasma membrane. Moreover, GLUT12 over‐expression in mice increases the whole‐body insulin sensitivity. Thus, GLUT12 has been proposed as a second insulin‐responsive glucose transporter. In obesity, GLUT12 is downregulated and does not respond to insulin. In contrast, GLUT12 is overexpressed in human solid tumors such as breast, prostate, gastric, liver and colon. High glucose concentration, insulin, and hypoxia upregulate GLUT12 both in adipocytes and tumor cells. Inhibition of GLUT12 mediated Warburg effect suppresses proliferation, migration, and invasion of cancer cells and xenografted tumors. This review summarizes the up-to-date information about GLUT12 physiological role and its implication in obesity and cancer, opening new perspectives to consider this transporter as a therapeutic target.