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Chi G, Dietz L, Tang H, Snee M, Scacioc A, Wang D, Mckinley G, Mukhopadhyay SM, Pike AC, Chalk R, Burgess-Brown NA, Timmermans JP, van Putte W, Robinson CV, Dürr KL. Structural characterization of human urea transporters UT-A and UT-B and their inhibition. SCIENCE ADVANCES 2023; 9:eadg8229. [PMID: 37774028 PMCID: PMC10541013 DOI: 10.1126/sciadv.adg8229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2023] [Accepted: 08/30/2023] [Indexed: 10/01/2023]
Abstract
In this study, we present the structures of human urea transporters UT-A and UT-B to characterize them at molecular level and to detail the mechanism of UT-B inhibition by its selective inhibitor, UTBinh-14. High-resolution structures of both transporters establish the structural basis for the inhibitor's selectivity to UT-B, and the identification of multiple binding sites for the inhibitor will aid with the development of drug lead molecules targeting both transporters. Our study also discovers phospholipids associating with the urea transporters by combining structural observations, native MS, and lipidomics analysis. These insights improve our understanding of urea transporter function at a molecular level and provide a blueprint for a structure-guided design of therapeutics targeting these transporters.
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Affiliation(s)
- Gamma Chi
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, UK
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Nuffield Department of Medicine Research Building, Oxford OX3 7FZ, UK
| | - Larissa Dietz
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, UK
| | - Haiping Tang
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford OX1 3QU, UK
| | - Matthew Snee
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, UK
| | - Andreea Scacioc
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, UK
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Nuffield Department of Medicine Research Building, Oxford OX3 7FZ, UK
| | - Dong Wang
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, UK
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Nuffield Department of Medicine Research Building, Oxford OX3 7FZ, UK
| | - Gavin Mckinley
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, UK
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Nuffield Department of Medicine Research Building, Oxford OX3 7FZ, UK
| | - Shubhashish M. M. Mukhopadhyay
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, UK
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Nuffield Department of Medicine Research Building, Oxford OX3 7FZ, UK
| | - Ashley C. W. Pike
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, UK
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Nuffield Department of Medicine Research Building, Oxford OX3 7FZ, UK
| | - Rod Chalk
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, UK
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Nuffield Department of Medicine Research Building, Oxford OX3 7FZ, UK
| | - Nicola A. Burgess-Brown
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, UK
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Nuffield Department of Medicine Research Building, Oxford OX3 7FZ, UK
| | - Jean-Pierre Timmermans
- Laboratory of Cell Biology and Histology (CBH) at Antwerp Centre for Advanced Microscopy (ACAM), Department of Veterinary Sciences, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Wouter van Putte
- Laboratory of Cell Biology and Histology (CBH) at Antwerp Centre for Advanced Microscopy (ACAM), Department of Veterinary Sciences, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
- PUXANO, Ottergemsesteenweg Zuid 713, 9000 Gent, Belgium
| | - Carol V. Robinson
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford OX1 3QU, UK
| | - Katharina L. Dürr
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, UK
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Nuffield Department of Medicine Research Building, Oxford OX3 7FZ, UK
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Abstract
The H(+) concentration in human blood is kept within very narrow limits, ~40 nmol/L, despite the fact that dietary metabolism generates acid and base loads that are added to the systemic circulation throughout the life of mammals. One of the primary functions of the kidney is to maintain the constancy of systemic acid-base chemistry. The kidney has evolved the capacity to regulate blood acidity by performing three key functions: (i) reabsorb HCO3(-) that is filtered through the glomeruli to prevent its excretion in the urine; (ii) generate a sufficient quantity of new HCO3(-) to compensate for the loss of HCO3(-) resulting from dietary metabolic H(+) loads and loss of HCO3(-) in the urea cycle; and (iii) excrete HCO3(-) (or metabolizable organic anions) following a systemic base load. The ability of the kidney to perform these functions requires that various cell types throughout the nephron respond to changes in acid-base chemistry by modulating specific ion transport and/or metabolic processes in a coordinated fashion such that the urine and renal vein chemistry is altered appropriately. The purpose of the article is to provide the interested reader with a broad review of a field that began historically ~60 years ago with whole animal studies, and has evolved to where we are currently addressing questions related to kidney acid-base regulation at the single protein structure/function level.
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Affiliation(s)
- Ira Kurtz
- Division of Nephrology, David Geffen School of Medicine, Los Angeles, CA; Brain Research Institute, UCLA, Los Angeles, CA
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Wall SM, Fischer MP, Glapion DM, De La Calzada M. ANG II reduces net acid secretion in rat outer medullary collecting duct. Am J Physiol Renal Physiol 2003; 285:F930-7. [PMID: 12851254 DOI: 10.1152/ajprenal.00400.2002] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In rat outer medullary collecting duct (OMCD), the mechanism(s) and regulation of H+ secretion are not understood fully. The effect of changes in acid-base balance and the renin-angiotensin system on net H+ secretion was explored. Rats received NaCl, NaHCO3, NH4Cl, or nothing in their drinking water for 7 days. Total ammonia and total CO2 (JtCO2) fluxes were measured in OMCD tubules perfused in vitro from rats in each treatment group. JtCO2 was reduced in tubules from rats drinking NH4Cl relative to those drinking NaHCO3. Because NH4Cl intake increases plasma renin and aldosterone, we asked if upregulation of the renin-angiotensin system reduces net H+ secretion. Deoxycorticosterone pivalate administered in vivo did not affect JtCO2. However, ANG II given in vivo at 0.1 ng/min reduced JtCO2 by 35%. To determine if ANG II has a direct effect on acid secretion, JtCO2 was measured with ANG II applied in vitro. ANG II (10-8 M) present in the bath solution reduced JtCO2 by 35%. This ANG II effect was not observed in the presence of the AT1 receptor blocker candesartan. In conclusion, in rat OMCD, JtCO2 is paradoxically reduced with NH4Cl ingestion. Increased circulating ANG II, as occurs during metabolic acidosis, reduces JtCO2.
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Affiliation(s)
- Susan M Wall
- Renal Division, Emory University School of Medicine, WMRB Rm. 338, 1639 Pierce Dr., N. E., Atlanta, GA 30322, USA.
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Tsuruoka S, Schwartz GJ. Metabolic acidosis stimulates H+ secretion in the rabbit outer medullary collecting duct (inner stripe) of the kidney. J Clin Invest 1997; 99:1420-31. [PMID: 9077552 PMCID: PMC507958 DOI: 10.1172/jci119301] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The outer medullary collecting duct (OMCD) absorbs HCO3- at high rates, but it is not clear if it responds to metabolic acidosis to increase H+ secretion. We measured net HCO3- transport in isolated perfused OMCDs taken from deep in the inner stripes of kidneys from control and acidotic (NH4Cl-fed for 3 d) rabbits. We used specific inhibitors to characterize the mechanisms of HCO3- transport: 10 microM Sch 28080 or luminal K+ removal to inhibit P-type H+,K+-ATPase activity, and 5-10 nM bafilomycin A1 or 1-10 nM concanamycin A to inhibit H+-ATPase activity. The results were comparable using either of each pair of inhibitors, and allowed us to show in control rabbits that 65% of net HCO3- absorption depended on H+-ATPase (H flux), and 35% depended on H+,K+-ATPase (H,K flux). Tubules from acidotic rabbits showed higher rates of HCO3- absorption (16.8+/-0.3 vs. 12.8+/-0.2 pmol/min per mm, P < 0.01). There was no difference in the H,K flux (5.9+/-0.2 vs. 5.8+/-0.2 pmol/min per mm), whereas there was a 61% higher H flux in segments from acidotic rabbits (11.3+/-0.2 vs. 7.0+/-0.2 pmol/min per mm, P < 0.01). Transport was then measured in other OMCDs before and after incubation for 1 h at pH 6.8, followed by 2 h at pH 7.4 (in vitro metabolic acidosis). Acid incubation in vitro stimulated HCO3- absorption (12.3+/-0.3 to 16.2+/-0.3 pmol/min per mm, P < 0.01), while incubation at pH 7.4 for 3 h did not change basal rate (11.8+/-0.4 to 11.7+/-0.4 pmol/min per mm). After acid incubation the H,K flux did not change, (4.7+/-0.4 to 4.6+/-0.4 pmol/min per mm), however, there was a 60% increase in H flux (6.6+/-0.3 to 10.8+/-0.3 pmol/min per mm, P < 0.01). In OMCDs from acidotic animals, and in OMCDs incubated in acid in vitro, there was a higher basal rate and a further increase in HCO3- absorption (16.7+/-0.4 to 21.3+/-0.3 pmol/min per mm, P < 0.01) because of increased H flux (11.5+/-0.3 to 15.7+/-0.2 pmol/min per mm, P < 0.01) without any change in H,K flux (5.4+/-0.3 to 5.6+/-0.3 pmol/min per mm). These data indicate that HCO3- absorption (H+ secretion) in OMCD is stimulated by metabolic acidosis in vivo and in vitro by an increase in H+-ATPase-sensitive HCO3- absorption. The mechanism of adaptation may involve increased synthesis and exocytosis to the apical membrane of proton pumps. This adaptation helps maintain homeostasis during metabolic acidosis.
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Affiliation(s)
- S Tsuruoka
- Department of Pediatrics, University of Rochester School of Medicine, New York 14642, USA
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Muto S, Yasoshima K, Yoshitomi K, Imai M, Asano Y. Electrophysiological identification of alpha- and beta-intercalated cells and their distribution along the rabbit distal nephron segments. J Clin Invest 1990; 86:1829-39. [PMID: 2254448 PMCID: PMC329815 DOI: 10.1172/jci114913] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
By cable analysis and intracellular microelectrode impalement in the in vitro perfused renal tubule, we identified alpha- and beta-intercalated (IC) cells along the rabbit distal nephron segments, including the connecting tubule (CNT), the cortical collecting duct (CCD), and the outer medullary collecting duct in the inner stripe (OMCDi). IC cells were distinguished from collecting duct (CD) cells by a relatively low basolateral membrane potential (VB), a higher fractional apical membrane resistance, and apparent high Cl- conductances of the basolateral membrane. Two functionally different subtypes of IC cells in the CCD were identified based on different responses of VB upon reduction of the perfusate Cl- from 120 to 12 mM: the basolateral membrane of beta-IC cells was hyperpolarized, whereas that of alpha-IC cells was unchanged. This is in accord with the hypothesis that the apical membrane of beta-IC cells contains some Cl(-)-dependent entry processes, possibly a Cl-/HCO3- exchanger. Further characterization of electrical properties of both subtypes of IC cells were performed upon lowering bath or perfusate Cl- from 120 to 12 mM, and raising bath or perfusate K+ from 5 to 50 mM. A 10-fold increase in the perfusate K+ had no effect on VB in both subtypes of IC cells. Upon abrupt changes in Cl- or K+ concentration in the bath, a large or a small depolarization of the basolateral membrane, respectively, was observed in both subtypes of IC cells. The electrical properties of alpha- and beta-IC cells were similar among the distal nephron segments, but their distribution was different: in the CNT, which consists of IC cells and CNT cells, 97.3% (36/37) of IC cells were of the beta type. In the CCD, which consists of IC cells and CD cells, 79.8% (79/99) of IC cells were of the beta-type, whereas in the OMCDi 100% (19/19) were of the alpha type, suggesting that the beta type predominates in the earlier and the alpha type in the later segment.
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Affiliation(s)
- S Muto
- Department of Nephrology, Jichi Medical School, Tochigi, Japan
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