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Aquaporins Display a Diversity in their Substrates. J Membr Biol 2023; 256:1-23. [PMID: 35986775 DOI: 10.1007/s00232-022-00257-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Accepted: 07/13/2022] [Indexed: 02/07/2023]
Abstract
Aquaporins constitute a family of transmembrane proteins that function to transport water and other small solutes across the cell membrane. Aquaporins family members are found in diverse life forms. Aquaporins share the common structural fold consisting of six transmembrane alpha helices with a central water-transporting channel. Four such monomers assemble together to form tetramers as their biological unit. Initially, aquaporins were discovered as water-transporting channels, but several studies supported their involvement in mediating the facilitated diffusion of different solutes. The so-called water channel is able to transport a variety of substrates ranging from a neutral molecule to a charged molecule or a small molecule to a bulky molecule or even a gas molecule. This article gives an overview of a diverse range of substrates conducted by aquaporin family members. Prime focus is on human aquaporins where aquaporins show a wide tissue distribution and substrate specificity leading to various physiological functions. This review also highlights the structural mechanisms leading to the transport of water and glycerol. More research is needed to understand how one common fold enables the aquaporins to transport an array of solutes.
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2
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Local Attraction of Substrates and Co-Substrates Enhances Weak Acid and Base Transmembrane Transport. Biomolecules 2022; 12:biom12121794. [PMID: 36551222 PMCID: PMC9775063 DOI: 10.3390/biom12121794] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 11/25/2022] [Accepted: 11/28/2022] [Indexed: 12/03/2022] Open
Abstract
The transmembrane transport of weak acid and base metabolites depends on the local pH conditions that affect the protonation status of the substrates and the availability of co-substrates, typically protons. Different protein designs ensure the attraction of substrates and co-substrates to the transporter entry sites. These include electrostatic surface charges on the transport proteins and complexation with seemingly transport-unrelated proteins that provide substrate and/or proton antenna, or enzymatically generate substrates in place. Such protein assemblies affect transport rates and directionality. The lipid membrane surface also collects and transfers protons. The complexity in the various systems enables adjustability and regulation in a given physiological or pathophysiological situation. This review describes experimentally shown principles in the attraction and facilitation of weak acid and base transport substrates, including monocarboxylates, ammonium, bicarbonate, and arsenite, plus protons as a co-substrate.
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3
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Geistlinger K, Schmidt JDR, Beitz E. Lactic Acid Permeability of Aquaporin-9 Enables Cytoplasmic Lactate Accumulation via an Ion Trap. Life (Basel) 2022; 12:life12010120. [PMID: 35054513 PMCID: PMC8779662 DOI: 10.3390/life12010120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Revised: 01/08/2022] [Accepted: 01/12/2022] [Indexed: 11/16/2022] Open
Abstract
(1) Background: Human aquaporin-9 (AQP9) conducts several small uncharged metabolites, such as glycerol, urea, and lactic acid. Certain brain tumors were shown to upregulate AQP9 expression, and the putative increase in lactic acid permeability was assigned to severity. (2) Methods: We expressed AQP9 and human monocarboxylate transporter 1 (MCT1) in yeast to determine the uptake rates and accumulation of radiolabeled l-lactate/l-lactic acid in different external pH conditions. (3) Results: The AQP9-mediated uptake of l-lactic acid was slow compared to MCT1 at neutral and slightly acidic pH, due to low concentrations of the neutral substrate species. At a pH corresponding to the pKa of l-lactic acid, uptake via AQP9 was faster than via MCT1. Substrate accumulation was fundamentally different between AQP9 and MCT1. With MCT1, an equilibrium was reached, at which the intracellular and extracellular l-lactate/H+ concentrations were balanced. Uptake via AQP9 was linear, theoretically yielding orders of magnitude of higher substrate accumulation than MCT1. (4) Conclusions: The selectivity of AQP9 for neutral l-lactic acid establishes an ion trap for l-lactate after dissociation. This may be physiologically relevant if the transmembrane proton gradient is steep, and AQP9 acts as the sole uptake path on at least one side of a polarized cell.
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4
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Schmidt JDR, Beitz E. Mutational Widening of Constrictions in a Formate-Nitrite/H + Transporter Enables Aquaporin-Like Water Permeability and Proton Conductance. J Biol Chem 2021; 298:101513. [PMID: 34929166 PMCID: PMC8749060 DOI: 10.1016/j.jbc.2021.101513] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Revised: 12/14/2021] [Accepted: 12/16/2021] [Indexed: 11/30/2022] Open
Abstract
The unrelated protein families of the microbial formate–nitrite transporters (FNTs) and aquaporins (AQP) likely adapted the same protein fold through convergent evolution. FNTs facilitate weak acid anion/H+ cotransport, whereas AQP water channels strictly exclude charged substrates including protons. The FNT channel–like transduction pathway bears two lipophilic constriction sites that sandwich a highly conserved histidine residue. Because of lacking experiments, the function of these constrictions is unclear, and the protonation status of the central histidine during substrate transport remains a matter of debate. Here, we introduced constriction-widening mutations into the prototypical FNT from Escherichia coli, FocA, and assayed formate/H+ transport properties, water/solute permeability, and proton conductance. We found that enlargement of these constrictions concomitantly decreased formate/formic acid transport. In contrast to wildtype FocA, the mutants were unable to make use of a transmembrane proton gradient as a driving force. A construct in which both constrictions were eliminated exhibited water permeability, similar to AQPs, although accompanied by a proton conductance. Our data indicate that the lipophilic constrictions mainly act as barriers to isolate the central histidine from the aqueous bulk preventing protonation via proton wires. These results are supportive of an FNT transport model in which the central histidine is uncharged, and weak acid substrate anion protonation occurs in the vestibule regions of the transporter before passing the constrictions.
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Affiliation(s)
- Jana D R Schmidt
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, 24118 Kiel, Germany
| | - Eric Beitz
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, 24118 Kiel, Germany.
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5
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Nerlich C, Epalle NH, Seick P, Beitz E. Discovery and Development of Inhibitors of the Plasmodial FNT-Type Lactate Transporter as Novel Antimalarials. Pharmaceuticals (Basel) 2021; 14:1191. [PMID: 34832972 PMCID: PMC8624176 DOI: 10.3390/ph14111191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 11/17/2021] [Accepted: 11/17/2021] [Indexed: 11/19/2022] Open
Abstract
Plasmodium spp. malaria parasites in the blood stage draw energy from anaerobic glycolysis when multiplying in erythrocytes. They tap the ample glucose supply of the infected host using the erythrocyte glucose transporter 1, GLUT1, and a hexose transporter, HT, of the parasite's plasma membrane. Per glucose molecule, two lactate anions and two protons are generated as waste that need to be released rapidly from the parasite to prevent blockage of the energy metabolism and acidification of the cytoplasm. Recently, the missing Plasmodium lactate/H+ cotransporter was identified as a member of the exclusively microbial formate-nitrite transporter family, FNT. Screening of an antimalarial compound selection with unknown targets led to the discovery of specific and potent FNT-inhibitors, i.e., pentafluoro-3-hydroxy-pent-2-en-1-ones. Here, we summarize the discovery and further development of this novel class of antimalarials, their modes of binding and action, circumvention of a putative resistance mutation of the FNT target protein, and suitability for in vivo studies using animal malaria models.
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Affiliation(s)
| | | | | | - Eric Beitz
- Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Gutenbergstr. 76, 24118 Kiel, Germany; (C.N.); (N.H.E.); (P.S.)
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6
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Structural characterization of the Plasmodium falciparum lactate transporter PfFNT alone and in complex with antimalarial compound MMV007839 reveals its inhibition mechanism. PLoS Biol 2021; 19:e3001386. [PMID: 34499638 PMCID: PMC8428694 DOI: 10.1371/journal.pbio.3001386] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Accepted: 08/04/2021] [Indexed: 02/05/2023] Open
Abstract
Plasmodium falciparum, the deadliest causal agent of malaria, caused more than half of the 229 million malaria cases worldwide in 2019. The emergence and spreading of frontline drug-resistant Plasmodium strains are challenging to overcome in the battle against malaria and raise urgent demands for novel antimalarial agents. The P. falciparum formate-nitrite transporter (PfFNT) is a potential drug target due to its housekeeping role in lactate efflux during the intraerythrocytic stage. Targeting PfFNT, MMV007839 was identified as a lead compound that kills parasites at submicromolar concentrations. Here, we present 2 cryogenic-electron microscopy (cryo-EM) structures of PfFNT, one with the protein in its apo form and one with it in complex with MMV007839, both at 2.3 Å resolution. Benefiting from the high-resolution structures, our study provides the molecular basis for both the lactate transport of PfFNT and the inhibition mechanism of MMV007839, which facilitates further antimalarial drug design.
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7
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Jakobowska I, Becker F, Minguzzi S, Hansen K, Henke B, Epalle NH, Beitz E, Hannus S. Fluorescence Cross-Correlation Spectroscopy Yields True Affinity and Binding Kinetics of Plasmodium Lactate Transport Inhibitors. Pharmaceuticals (Basel) 2021; 14:ph14080757. [PMID: 34451854 PMCID: PMC8399565 DOI: 10.3390/ph14080757] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 07/27/2021] [Accepted: 07/28/2021] [Indexed: 01/13/2023] Open
Abstract
Blocking lactate export in the parasitic protozoan Plasmodium falciparum is a novel strategy to combat malaria. We discovered small drug-like molecules that inhibit the sole plasmodial lactate transporter, PfFNT, and kill parasites in culture. The pentafluoro-3-hydroxy-pent-2-en-1-one BH296 blocks PfFNT with nanomolar efficiency but an in vitro selected PfFNT G107S mutation confers resistance against the drug. We circumvented the mutation by introducing a nitrogen atom as a hydrogen bond acceptor site into the aromatic ring of the inhibitor yielding BH267.meta. The current PfFNT inhibitor efficiency values were derived from yeast-based lactate transport assays, yet direct affinity and binding kinetics data are missing. Here, we expressed PfFNT fused with a green fluorescent protein in human embryonic kidney cells and generated fluorescent derivatives of the inhibitors, BH296 and BH267.meta. Using confocal imaging, we confirmed the location of the proposed binding site at the cytosolic transporter entry site. We then carried out fluorescence cross-correlation spectroscopy measurements to assign true Ki-values, as well as kon and koff rate constants for inhibitor binding to PfFNT wildtype and the G107S mutant. BH296 and BH267.meta gave similar rate constants for binding to PfFNT wildtype. BH296 was inactive on PfFNT G107S, whereas BH267.meta bound the mutant protein albeit with weaker affinity than to PfFNT wildtype. Eventually, using a set of PfFNT inhibitor compounds, we found a robust correlation of the results from the biophysical FCCS binding assay to inhibition data of the functional transport assay.
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Affiliation(s)
- Iga Jakobowska
- Intana Bioscience GmbH, Lochhamer Str. 29a, 82152 Planegg, Germany; (I.J.); (F.B.); (S.M.); (K.H.)
| | - Frank Becker
- Intana Bioscience GmbH, Lochhamer Str. 29a, 82152 Planegg, Germany; (I.J.); (F.B.); (S.M.); (K.H.)
| | - Stefano Minguzzi
- Intana Bioscience GmbH, Lochhamer Str. 29a, 82152 Planegg, Germany; (I.J.); (F.B.); (S.M.); (K.H.)
| | - Kerrin Hansen
- Intana Bioscience GmbH, Lochhamer Str. 29a, 82152 Planegg, Germany; (I.J.); (F.B.); (S.M.); (K.H.)
| | - Björn Henke
- Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Gutenbergstr. 76, 24118 Kiel, Germany; (B.H.); (N.H.E.)
| | - Nathan Hugo Epalle
- Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Gutenbergstr. 76, 24118 Kiel, Germany; (B.H.); (N.H.E.)
| | - Eric Beitz
- Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Gutenbergstr. 76, 24118 Kiel, Germany; (B.H.); (N.H.E.)
- Correspondence: (E.B.); (S.H.)
| | - Stefan Hannus
- Intana Bioscience GmbH, Lochhamer Str. 29a, 82152 Planegg, Germany; (I.J.); (F.B.); (S.M.); (K.H.)
- Correspondence: (E.B.); (S.H.)
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Köpnick AL, Geistlinger K, Beitz E. Cysteine 159 delineates a hinge region of the alternating access monocarboxylate transporter 1 and is targeted by cysteine-modifying inhibitors. FEBS J 2021; 288:6052-6062. [PMID: 33999492 DOI: 10.1111/febs.16024] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Revised: 04/14/2021] [Accepted: 05/14/2021] [Indexed: 12/16/2022]
Abstract
Monocarboxylate transporter isoforms 1-4, MCT, of the solute carrier SLC16A family facilitate proton-coupled transport of l-lactate. Growth of tumors that exhibit the Warburg effect, that is, high rates of anaerobic glycolysis despite availability of oxygen, relies on swift l-lactate export, whereas oxygenic cancer cells import circulating l-lactate as a fuel. Currently, MCTs are viewed as promising anticancer targets. Small-molecule inhibitors have been found, and, recently, high-resolution protein structures have been obtained. Key questions, however, regarding the exact binding sites of cysteine-modifying inhibitors and the substrate translocation cycle lack a conclusive experimental basis. Here, we report Cys159 of the ubiquitous human MCT1 to reside in a critical hinge region of the alternating access-type transporter. We identified Cys159 as the binding site of the organomercurial pCMBS. The inhibitory effect of pCMBS was proposed to be indirect via modification of the chaperone basigin. We provide evidence that pCMBS locks MCT1 in its outward open conformation in a wedge-like fashion. We corroborated this finding using smaller cysteine-modifying reagents that size-dependently inhibited l-lactate transport. The smallest modifiers targeted additional cysteines as shown by a C159S mutant. We found a Cys399/Cys400 pair to constitute the second hinge of the transporter that tolerated only individual replacement by serine. The hinge cysteines, in particular the selectively addressable Cys159, provide natural anchors for placing probes into MCTs to report, for instance, on the electrostatics or hydration upon binding of the transported l-lactate substrate and the proton cosubstrate.
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Affiliation(s)
- Anna-Lena Köpnick
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Germany
| | - Katharina Geistlinger
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Germany
| | - Eric Beitz
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Germany
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9
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Walloch P, Hansen C, Priegann T, Schade D, Beitz E. Pentafluoro-3-hydroxy-pent-2-en-1-ones Potently Inhibit FNT-Type Lactate Transporters from all Five Human-Pathogenic Plasmodium Species. ChemMedChem 2021; 16:1283-1289. [PMID: 33336890 PMCID: PMC8247949 DOI: 10.1002/cmdc.202000952] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Indexed: 12/16/2022]
Abstract
The protozoan parasite Plasmodium falciparum causes the most severe and prevailing form of malaria in sub-Saharan Africa. Previously, we identified the plasmodial lactate transporter, PfFNT, a member of the microbial formate-nitrite transporter family, as a novel antimalarial drug target. With the pentafluoro-3-hydroxy-pent-2-en-1-ones, we discovered PfFNT inhibitors that potently kill P. falciparum parasites in vitro. Four additional human-pathogenic Plasmodium species require attention, that is, P. vivax, most prevalent outside of Africa, and the regional P. malariae, P. ovale and P. knowlesi. Herein, we show that the plasmodial FNT variants are highly similar in terms of protein sequence and functionality. The FNTs from all human-pathogenic plasmodia and the rodent malaria parasite were efficiently inhibited by pentafluoro-3-hydroxy-pent-2-en-1-ones. We further established a phenotypic yeast-based FNT inhibitor screen, and found very low compound cytotoxicity and monocarboxylate transporter 1 off-target activity on human cells, particularly of the most potent FNT inhibitor BH267.meta, allowing these compounds to proceed towards animal model malaria studies.
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Affiliation(s)
- Philipp Walloch
- Department of Pharmaceutical and Medicinal ChemistryChristian-Albrechts-University of KielGutenbergstr. 7624118KielGermany
| | - Christian Hansen
- Department of Pharmaceutical and Medicinal ChemistryChristian-Albrechts-University of KielGutenbergstr. 7624118KielGermany
| | - Till Priegann
- Department of Pharmaceutical and Medicinal ChemistryChristian-Albrechts-University of KielGutenbergstr. 7624118KielGermany
| | - Dennis Schade
- Department of Pharmaceutical and Medicinal ChemistryChristian-Albrechts-University of KielGutenbergstr. 7624118KielGermany
| | - Eric Beitz
- Department of Pharmaceutical and Medicinal ChemistryChristian-Albrechts-University of KielGutenbergstr. 7624118KielGermany
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Köpnick AL, Jansen A, Geistlinger K, Epalle NH, Beitz E. Basigin drives intracellular accumulation of l-lactate by harvesting protons and substrate anions. PLoS One 2021; 16:e0249110. [PMID: 33770122 PMCID: PMC7996999 DOI: 10.1371/journal.pone.0249110] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Accepted: 03/11/2021] [Indexed: 12/22/2022] Open
Abstract
Transmembrane transport of l-lactate by members of the monocarboxylate transporter family, MCT, is vital in human physiology and a malignancy factor in cancer. Interaction with an accessory protein, typically basigin, is required to deliver the MCT to the plasma membrane. It is unknown whether basigin additionally exerts direct effects on the transmembrane l-lactate transport of MCT1. Here, we show that the presence of basigin leads to an intracellular accumulation of l-lactate 4.5-fold above the substrate/proton concentrations provided by the external buffer. Using basigin truncations we localized the effect to arise from the extracellular Ig-I domain. Identification of surface patches of condensed opposite electrostatic potential, and experimental analysis of charge-affecting Ig-I mutants indicated a bivalent harvesting antenna functionality for both, protons and substrate anions. From these data, and determinations of the cytosolic pH with a fluorescent probe, we conclude that the basigin Ig-I domain drives lactate uptake by locally increasing the proton and substrate concentration at the extracellular MCT entry site. The biophysical properties are physiologically relevant as cell growth on lactate media was strongly promoted in the presence of the Ig-I domain. Lack of the domain due to shedding, or misfolding due to breakage of a stabilizing disulfide bridge reversed the effect. Tumor progression according to classical or reverse Warburg effects depends on the transmembrane l-lactate distribution, and this study shows that the basigin Ig-I domain is a pivotal determinant.
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Affiliation(s)
- Anna-Lena Köpnick
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, Germany
| | - Annika Jansen
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, Germany
| | - Katharina Geistlinger
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, Germany
| | - Nathan Hugo Epalle
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, Germany
| | - Eric Beitz
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, Germany
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11
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Schmidt JDR, Walloch P, Höger B, Beitz E. Aquaporins with lactate/lactic acid permeability at physiological pH conditions. Biochimie 2021; 188:7-11. [PMID: 33577940 DOI: 10.1016/j.biochi.2021.01.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2020] [Revised: 01/15/2021] [Accepted: 01/19/2021] [Indexed: 10/22/2022]
Abstract
The spectrum of putative and experimentally shown permeants of cellular water and solute channels of the ubiquitous aquaporin family is still increasing. Virtually all AQP substrates, e.g. water, glycerol, urea, hydrogen peroxide, or carbon dioxide, are permanently neutral small molecule compounds. Several reports, however, describe aquaporins that exhibit lactate permeability. Lactate in aqueous solution undergoes a pH-dependent protonation equilibrium with neutral lactic acid, which likely represents the actual substrate form passing the aquaporin channel. Certain aquaporins, however, appear to be better geared for lactate/lactic acid permeability even at low proton availability. Here, we discuss the structural properties of such aquaporins and compare them to the microbial protein family of the formate-nitrite (lactate) transporters that assume the aquaporin fold despite unrelated protein sequences.
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Affiliation(s)
- Jana D R Schmidt
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, Germany
| | - Philipp Walloch
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, Germany
| | - Bastian Höger
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, Germany
| | - Eric Beitz
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, Germany.
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12
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Lyu M, Su CC, Kazura JW, Yu EW. Structural basis of transport and inhibition of the Plasmodium falciparum transporter PfFNT. EMBO Rep 2021; 22:e51628. [PMID: 33471955 DOI: 10.15252/embr.202051628] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Revised: 12/07/2020] [Accepted: 12/10/2020] [Indexed: 12/14/2022] Open
Abstract
The intra-erythrocyte stage of P. falciparum relies primarily on glycolysis to generate adenosine triphosphate (ATP) and the energy required to support growth and reproduction. Lactic acid, a metabolic byproduct of glycolysis, is potentially toxic as it lowers the pH inside the parasite. Plasmodium falciparum formate-nitrite transporter (PfFNT), a 34-kDa transmembrane protein, has been identified as a novel drug target as it exports lactate from inside the parasite to the surrounding parasitophorous vacuole within the erythrocyte cytosol. The structure and detailed molecular mechanism of this membrane protein are not yet available. Here we present structures of PfFNT in the absence and presence of the functional inhibitor MMV007839 at resolutions of 2.56 Å and 2.78 Å using single-particle cryo-electron microscopy. Genetic analysis and transport assay indicate that PfFNT is able to transfer lactate across the membrane. Combined, our data suggest a stepwise displacement mechanism for substrate transport. The PfFNT membrane protein is capable of picking up lactate ions from the parasite's cytosol, converting them to lactic acids and then exporting these acids into the extracellular space.
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Affiliation(s)
- Meinan Lyu
- Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Chih-Chia Su
- Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - James W Kazura
- Center for Global Health & Diseases, Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Edward W Yu
- Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, OH, USA
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13
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The Ionophores CCCP and Gramicidin but Not Nigericin Inhibit Trypanosoma brucei Aquaglyceroporins at Neutral pH. Cells 2020; 9:cells9102335. [PMID: 33096791 PMCID: PMC7589649 DOI: 10.3390/cells9102335] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 10/16/2020] [Accepted: 10/20/2020] [Indexed: 12/16/2022] Open
Abstract
Human African trypanosomiasis (HAT) is caused by Trypanosoma brucei parasites. The T. brucei aquaglyceroporin isoform 2, TbAQP2, has been linked to the uptake of pentamidine. Negative membrane potentials and transmembrane pH gradients were suggested to promote transport of the dicationic antitrypanosomal drug. Application of ionophores to trypanosomes further hinted at direct inhibition of TbAQP2 by carbonyl cyanide m-chlorophenyl hydrazone (CCCP). Here, we tested for direct effects of three classical ionophores (CCCP, nigericin, gramicidin) on the functionality of TbAQP2 and the related TbAQP3 at conditions that are independent from the membrane potential or a proton gradient. We expressed TbAQP2 and TbAQP3 in yeast, and determined permeability of uncharged glycerol at neutral pH using stopped-flow light scattering. The mobile proton carrier CCCP directly inhibited TbAQP2 glycerol permeability at an IC50 of 2 µM, and TbAQP3 to a much lesser extent (IC50 around 1 mM) likely due to different selectivity filter layouts. Nigericin, another mobile carrier, left both isoforms unaffected. The membrane-integral pore-forming gramicidin evenly inhibited TbAQP2 and TbAQP2 in the double-digit micromolar range. Our data exemplify the need for suitable controls to detect unwanted ionophore side effects even when used at concentrations that are typically recommended to disturb the transmembrane ion distribution.
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