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Rimon A, Amartely H, Padan E. The crossing of two unwound transmembrane regions that is the hallmark of the NhaA structural fold is critical for antiporter activity. Sci Rep 2024; 14:5915. [PMID: 38467695 PMCID: PMC10928194 DOI: 10.1038/s41598-024-56425-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Accepted: 03/06/2024] [Indexed: 03/13/2024] Open
Abstract
Cell pH and Na+ homeostasis requires Na+/H+ antiporters. The crystal structure of NhaA, the main Escherichia coli Na+/H+ antiporter, revealed a unique NhaA structural fold shared by prokaryotic and eukaryotic membrane proteins. Out of the 12 NhaA transmembrane segments (TMs), TMs III-V and X-XII are topologically inverted repeats with unwound TMs IV and XI forming the X shape characterizing the NhaA fold. We show that intramolecular cross-linking under oxidizing conditions of a NhaA mutant with two Cys replacements across the crossing (D133C-T340C) inhibits antiporter activity and impairs NhaA-dependent cell growth in high-salts. The affinity purified D133C-T340C protein binds Li+ (the Na+ surrogate substrate of NhaA) under reducing conditions. The cross-linking traps the antiporter in an outward-facing conformation, blocking the antiport cycle. As many secondary transporters are found to share the NhaA fold, including some involved in human diseases, our data have importance for both basic and clinical research.
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Affiliation(s)
- Abraham Rimon
- Department of Biological Chemistry, Alexander Silberman Institute of Life Sciences, Jerusalem, Israel
- The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, 91904, Jerusalem, Israel
| | - Hadar Amartely
- Wolfson Center for Applied Structural Biology, Jerusalem, Israel
- The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, 91904, Jerusalem, Israel
| | - Etana Padan
- Department of Biological Chemistry, Alexander Silberman Institute of Life Sciences, Jerusalem, Israel.
- The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, 91904, Jerusalem, Israel.
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2
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Ruiz Munevar M, Rizzi V, Portioli C, Vidossich P, Cao E, Parrinello M, Cancedda L, De Vivo M. Cation Chloride Cotransporter NKCC1 Operates through a Rocking-Bundle Mechanism. J Am Chem Soc 2024; 146:552-566. [PMID: 38146212 PMCID: PMC10786066 DOI: 10.1021/jacs.3c10258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Revised: 12/05/2023] [Accepted: 12/06/2023] [Indexed: 12/27/2023]
Abstract
The sodium, potassium, and chloride cotransporter 1 (NKCC1) plays a key role in tightly regulating ion shuttling across cell membranes. Lately, its aberrant expression and function have been linked to numerous neurological disorders and cancers, making it a novel and highly promising pharmacological target for therapeutic interventions. A better understanding of how NKCC1 dynamically operates would therefore have broad implications for ongoing efforts toward its exploitation as a therapeutic target through its modulation. Based on recent structural data on NKCC1, we reveal conformational motions that are key to its function. Using extensive deep-learning-guided atomistic simulations of NKCC1 models embedded into the membrane, we captured complex dynamical transitions between alternate open conformations of the inner and outer vestibules of the cotransporter and demonstrated that NKCC1 has water-permeable states. We found that these previously undefined conformational transitions occur via a rocking-bundle mechanism characterized by the cooperative angular motion of transmembrane helices (TM) 4 and 9, with the contribution of the extracellular tip of TM 10. We found these motions to be critical in modulating ion transportation and in regulating NKCC1's water transporting capabilities. Specifically, we identified interhelical dynamical contacts between TM 10 and TM 6, which we functionally validated through mutagenesis experiments of 4 new targeted NKCC1 mutants. We conclude showing that those 4 residues are highly conserved in most Na+-dependent cation chloride cotransporters (CCCs), which highlights their critical mechanistic implications, opening the way to new strategies for NKCC1's function modulation and thus to potential drug action on selected CCCs.
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Affiliation(s)
- Manuel
José Ruiz Munevar
- Laboratory
of Molecular Modelling & Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
| | - Valerio Rizzi
- Biomolecular
& Pharmaceutical Modelling Group, Université
de Genève, Rue Michel-Servet 1, Geneva CH-1211 4, Switzerland
| | - Corinne Portioli
- Laboratory
of Nanotechnology for Precision Medicine, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
- Laboratory
of Brain Development and Disease, Istituto
Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
| | - Pietro Vidossich
- Laboratory
of Molecular Modelling & Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
| | - Erhu Cao
- Department
of Biochemistry, University of Utah School
of Medicine, Salt Lake City, Utah 84112-5650, United States
| | - Michele Parrinello
- Laboratory
of Atomistic Simulations, Istituto Italiano
di Tecnologia, Via Morego 30, Genoa 16163, Italy
| | - Laura Cancedda
- Laboratory
of Brain Development and Disease, Istituto
Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
| | - Marco De Vivo
- Laboratory
of Molecular Modelling & Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
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Prokaryotic Na+/H+ Exchangers—Transport Mechanism and Essential Residues. Int J Mol Sci 2022; 23:ijms23169156. [PMID: 36012428 PMCID: PMC9408914 DOI: 10.3390/ijms23169156] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Revised: 08/09/2022] [Accepted: 08/13/2022] [Indexed: 11/16/2022] Open
Abstract
Na+/H+ exchangers are essential for Na+ and pH homeostasis in all organisms. Human Na+/H+ exchangers are of high medical interest, and insights into their structure and function are aided by the investigation of prokaryotic homologues. Most prokaryotic Na+/H+ exchangers belong to either the Cation/Proton Antiporter (CPA) superfamily, the Ion Transport (IT) superfamily, or the Na+-translocating Mrp transporter superfamily. Several structures have been solved so far for CPA and Mrp members, but none for the IT members. NhaA from E. coli has served as the prototype of Na+/H+ exchangers due to the high amount of structural and functional data available. Recent structures from other CPA exchangers, together with diverse functional information, have allowed elucidation of some common working principles shared by Na+/H+ exchangers from different families, such as the type of residues involved in the substrate binding and even a simple mechanism sufficient to explain the pH regulation in the CPA and IT superfamilies. Here, we review several aspects of prokaryotic Na+/H+ exchanger structure and function, discussing the similarities and differences between different transporters, with a focus on the CPA and IT exchangers. We also discuss the proposed transport mechanisms for Na+/H+ exchangers that explain their highly pH-regulated activity profile.
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Mondal R, Rimon A, Masrati G, Ben-Tal N, Friedler A, Padan E. Towards Molecular Understanding of the pH Dependence Characterizing NhaA of Which Structural Fold is Shared by Other Transporters. J Mol Biol 2021; 433:167156. [PMID: 34273399 DOI: 10.1016/j.jmb.2021.167156] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2021] [Revised: 06/19/2021] [Accepted: 07/08/2021] [Indexed: 11/25/2022]
Abstract
Na+/H+ antiporters comprise a super-family (CPA) of membrane proteins that are found in all kingdoms of life and are essential in cellular homeostasis of pH, Na+ and volume. Their activity is strictly dependent on pH, a property that underpins their role in pH homeostasis. While several human homologues have long been drug targets, NhaA of Escherichia coli has become the paradigm for this class of secondary active transporters as NhaA crystal structure provided insight into the architecture of this molecular machine. However, the mechanism of the strict pH dependence of NhaA is missing. Here, as a follow up of a recent evolutionary analysis that identified a 'CPA motif', we rationally designed three E. coli NhaA mutants: D133S, I134T, and the double mutant D133S-I134T. Exploring growth phenotype, transport activity and Li+-binding of the mutants, we revealed that Asp133 does not participate directly in proton binding, nor does it directly dictate the pH-dependent transport of NhaA. Strikingly, the variant I134T lost some of the pH control, and the D133S-Il134T double mutant retained Li+ binding in a pH independent fashion. Concurrent to loss of pH control, these mutants bound Li+ more strongly than the WT. Both positions are in close vicinity to the ion-binding site of the antiporter, attributing the results to electrostatic interaction between these residues and Asp164 of the ion-binding site. This is consistent with pH sensing resulting from direct coupling between cation binding and deprotonation in Asp164, which applies also to other CPA antiporters that are involved in human diseases.
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Affiliation(s)
- R Mondal
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel
| | - A Rimon
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel
| | - G Masrati
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv, 69978 Tel-Aviv, Israel
| | - N Ben-Tal
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv, 69978 Tel-Aviv, Israel
| | - A Friedler
- Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel
| | - E Padan
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel.
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Quick M, Dwivedi M, Padan E. Insight into the direct interaction of Na + with NhaA and mechanistic implications. Sci Rep 2021; 11:7045. [PMID: 33782459 PMCID: PMC8007835 DOI: 10.1038/s41598-021-86318-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Accepted: 03/05/2021] [Indexed: 11/21/2022] Open
Abstract
Na+/H+ antiporters comprise a family of membrane proteins evolutionarily conserved in all kingdoms of life that are essential in cellular ion homeostasis. While several human homologues have long been drug targets, NhaA of Escherichia coli has become the paradigm for this class of secondary active transporters as NhaA crystals provided insight in the structure of this molecular machine. However, structural data revealing the composition of the binding site for Na+ (or its surrogate Li+) is missing, representing a bottleneck in our understanding of the correlation between the structure and function of NhaA. Here, by adapting the scintillation proximity assay (SPA) for direct determination of Na+ binding to NhaA, we revealed that (i) NhaA is well adapted as the main antiporter for Na+ homeostasis in Escherichia coli and possibly in other bacteria as the cytoplasmic Na+ concentration is similar to the Na+ binding affinity of NhaA, (ii) experimental conditions affect NhaA-mediated cation binding, (iii) in addition to Na+ and Li+, the halide Tl+ interacts with NhaA, (iv) whereas acidic pH inhibits maximum binding of Na+ to NhaA, partial Na+ binding by NhaA is independent of the pH, an important novel insight into the effect of pH on NhaA cation binding.
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Affiliation(s)
- Matthias Quick
- Department of Psychiatry and Center for Molecular Recognition, Columbia University Vagelos College of Physicians and Surgeons, and New York State Psychiatric Institute, New York, NY, 10032, USA.
| | - Manish Dwivedi
- Department of Biological Chemistry, Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, 91904, Jerusalem, Israel.,Amity Institute of Biotechnology, Amity University Uttar Pradesh, Lucknow, 226028, India
| | - Etana Padan
- Department of Biological Chemistry, Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, 91904, Jerusalem, Israel.
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