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Zhang S, Fu C, Luo Y, Xie Q, Xu T, Sun Z, Su Z, Zhou X. Cryo-EM structure of a eukaryotic zinc transporter at a low pH suggests its Zn 2+-releasing mechanism. J Struct Biol 2023; 215:107926. [PMID: 36464198 DOI: 10.1016/j.jsb.2022.107926] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Revised: 11/10/2022] [Accepted: 11/28/2022] [Indexed: 12/04/2022]
Abstract
Zinc transporter 8 (ZnT8) is mainly expressed in pancreatic islet β cells and is responsible for H+-coupled uptake (antiport) of Zn2+ into the lumen of insulin secretory granules. Structures of human ZnT8 and its prokaryotic homolog YiiP have provided structural basis for constructing a plausible transport cycle for Zn2+. However, the mechanistic role that protons play in the transport process remains unclear. Here we present a lumen-facing cryo-EM structure of ZnT8 from Xenopus tropicalis (xtZnT8) in the presence of Zn2+ at a luminal pH (5.5). Compared to a Zn2+-bound xtZnT8 structure at a cytosolic pH (7.5), the low-pH structure displays an empty transmembrane Zn2+-binding site with a disrupted coordination geometry. Combined with a Zn2+-binding assay our data suggest that protons may disrupt Zn2+ coordination at the transmembrane Zn2+-binding site in the lumen-facing state, thus facilitating Zn2+ release from ZnT8 into the lumen.
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Affiliation(s)
- Senfeng Zhang
- Department of Integrated Traditional Chinese and Western Medicine, Rare Diseases Center, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Chunting Fu
- Department of Integrated Traditional Chinese and Western Medicine, Rare Diseases Center, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Yongbo Luo
- The State Key Laboratory of Biotherapy, Department of Geriatrics and National Clinical Research Center for Geriatrics, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Qingrong Xie
- Department of Integrated Traditional Chinese and Western Medicine, Rare Diseases Center, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Tong Xu
- Department of Integrated Traditional Chinese and Western Medicine, Rare Diseases Center, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Ziyi Sun
- Department of Integrated Traditional Chinese and Western Medicine, Rare Diseases Center, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China.
| | - Zhaoming Su
- The State Key Laboratory of Biotherapy, Department of Geriatrics and National Clinical Research Center for Geriatrics, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China.
| | - Xiaoming Zhou
- Department of Integrated Traditional Chinese and Western Medicine, Rare Diseases Center, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China.
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2
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Giangregorio N, Pierri CL, Tonazzi A, Incampo G, Tragni V, De Grassi A, Indiveri C. Proline/Glycine residues of the PG-levels guide conformational changes along the transport cycle in the mitochondrial carnitine/acylcarnitine carrier (SLC25A20). Int J Biol Macromol 2022; 221:1453-1465. [PMID: 36122779 DOI: 10.1016/j.ijbiomac.2022.09.135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2022] [Revised: 09/05/2022] [Accepted: 09/15/2022] [Indexed: 11/19/2022]
Abstract
Mitochondrial carnitine/acylcarnitine carrier (CAC) is a member of the mitochondrial carrier (MC) family and imports acylcarnitine into the mitochondrial matrix in exchange for carnitine, playing a pivotal role in carnitine shuttle, crucial for fatty acid oxidation. The crystallized structure of CAC has not been solved yet, however, the availability of several in vitro/in silico studies, also based on the crystallized structures of the ADP/ATP carrier in the cytosolic-conformation and in the matrix-conformation, has made possible to confirm the hypothesis of the single-binding centered-gated pore mechanism for all the members of the MC family. In addition, our recent bioinformatics analyses allowed quantifying in silico the importance of protein residues of MC substrate binding region, of those involved in the formation of the matrix and cytosolic gates, and of those belonging to the Pro/Gly (PG) levels, proposed to be crucial for the tilting/kinking/bending of the six MC transmembrane helices, funneling the substrate translocation pathway. Here we present a combined in silico/in vitro analysis employed for investigating the role played by a group of 6 proline residues and 6 glycine residues, highly conserved in CAC, belonging to MC PG-levels. Residues of the PG-levels surround the similarly located MC common substrate binding region, and were proposed to lead conformational changes and substrate translocation, following substrate binding. For our analysis, we employed 3D molecular modeling approaches, alanine scanning site-directed mutagenesis and in vitro transport assays. Our analysis reveals that P130 (H3), G268 (H6) and G220 (H5), mutated in alanine, affect severely CAC transport activity (mutant catalytic efficiency lower than 5 % compared to the wild type CAC), most likely due to their major role in triggering CAC conformational changes, following carnitine binding. Notably, P30A (H1) and G121A (H3) CAC mutants, increase the carnitine uptake up to 217 % and 112 %, respectively, compared to the wild type CAC.
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Affiliation(s)
- Nicola Giangregorio
- CNR Institute of Biomembranes, Bioenergetics and Molecular Biotechnologies (IBIOM), Via Amendola 122/O, 70126 Bari, Italy.
| | - Ciro Leonardo Pierri
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Italy, Via E. Orabona, 4, 70126 Bari, Italy.
| | - Annamaria Tonazzi
- CNR Institute of Biomembranes, Bioenergetics and Molecular Biotechnologies (IBIOM), Via Amendola 122/O, 70126 Bari, Italy
| | - Giovanna Incampo
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Italy, Via E. Orabona, 4, 70126 Bari, Italy
| | - Vincenzo Tragni
- CNR Institute of Biomembranes, Bioenergetics and Molecular Biotechnologies (IBIOM), Via Amendola 122/O, 70126 Bari, Italy; Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Italy, Via E. Orabona, 4, 70126 Bari, Italy
| | - Anna De Grassi
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Italy, Via E. Orabona, 4, 70126 Bari, Italy
| | - Cesare Indiveri
- CNR Institute of Biomembranes, Bioenergetics and Molecular Biotechnologies (IBIOM), Via Amendola 122/O, 70126 Bari, Italy; Department DiBEST (Biologia, Ecologia, Scienze della Terra) Unit of Biochemistry and Molecular Biotechnology, University of Calabria, Via Bucci 4C, 87036 Arcavacata di Rende, Italy
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3
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Millan CR, Francis M, Khandelwal NK, Thompson VF, Thaker TM, Tomasiak TM. A Conserved Motif in Intracellular Loop 1 Stabilizes the Outward-Facing Conformation of TmrAB. J Mol Biol 2021; 433:166834. [PMID: 33524413 DOI: 10.1016/j.jmb.2021.166834] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Revised: 01/14/2021] [Accepted: 01/15/2021] [Indexed: 02/05/2023]
Abstract
The ATP binding cassette (ABC) family of transporters moves small molecules (lipids, sugars, peptides, drugs, nutrients) across membranes in nearly all organisms. Transport activity requires conformational switching between inward-facing and outward-facing states driven by ATP-dependent dimerization of two nucleotide binding domains (NBDs). The mechanism that connects ATP binding and hydrolysis in the NBDs to conformational changes in a substrate binding site in the transmembrane domains (TMDs) is currently an outstanding question. Here we use sequence coevolution analyses together with biochemical characterization to investigate the role of a highly conserved region in intracellular loop 1 we define as the GRD motif in coordinating domain rearrangements in the heterodimeric peptide exporter from Thermus thermophilus, TmrAB. Mutations in the GRD motif alter ATPase activity as well as transport. Disulfide crosslinking, evolutionary trace, and evolutionary coupling analysis reveal that these effects are likely due to the destabilization of a network in which the GRD motif in TmrA bridges residues of the Q-loop, X-loop, and ABC motif in the NBDs to residues in the TmrAB peptide substrate binding site, thus providing an avenue for conformational coupling. We further find that disruption of this network in TmrA versus TmrB has different functional consequences, hinting at an intrinsic asymmetry in heterodimeric ABC transporters extending beyond that of the NBDs. These results support a mechanism in which the GRD motifs help coordinate a transition to an outward open conformation, and each half of the transporter likely plays a different role in the conformational cycle of TmrAB.
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Affiliation(s)
- Cinthia R Millan
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA.
| | - Martina Francis
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA.
| | | | - Valery F Thompson
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA.
| | - Tarjani M Thaker
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA.
| | - Thomas M Tomasiak
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA.
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Szöllősi D, Rose-Sperling D, Hellmich UA, Stockner T. Comparison of mechanistic transport cycle models of ABC exporters. Biochim Biophys Acta Biomembr 2017; 1860:818-832. [PMID: 29097275 PMCID: PMC7610611 DOI: 10.1016/j.bbamem.2017.10.028] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Revised: 10/23/2017] [Accepted: 10/25/2017] [Indexed: 12/25/2022]
Abstract
ABC (ATP binding cassette) transporters, ubiquitous in all kingdoms of life, carry out essential substrate transport reactions across cell membranes. Their transmembrane domains bind and translocate substrates and are connected to a pair of nucleotide binding domains, which bind and hydrolyze ATP to energize import or export of substrates. Over four decades of investigations into ABC transporters have revealed numerous details from atomic-level structural insights to their functional and physiological roles. Despite all these advances, a comprehensive understanding of the mechanistic principles of ABC transporter function remains elusive. The human multidrug resistance transporter ABCB1, also referred to as P-glycoprotein (P-gp), is one of the most intensively studied ABC exporters. Using ABCB1 as the reference point, we aim to compare the dominating mechanistic models of substrate transport and ATP hydrolysis for ABC exporters and to highlight the experimental and computational evidence in their support. In particular, we point out in silico studies that enhance and complement available biochemical data. “This article is part of a Special Issue entitled: Beyond the Structure Function Horizon of Membrane Proteins edited by Ute Hellmich, Rupak Doshi and Benjamin McIlwain.”
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Affiliation(s)
- Dániel Szöllősi
- Medical University of Vienna, Institute of Pharmacology, Waehringerstr. 13A, Vienna 1090, Austria
| | - Dania Rose-Sperling
- Johannes Gutenberg-University, Department of Pharmacy and Biochemistry, Johann-Joachim-Becher-Weg 30, Mainz 55128, Germany; Centre for Biomolecular Magnetic Resonance (BMRZ), Goethe-University Frankfurt, Max von Laue-Str. 9, 60438 Frankfurt am Main, Germany
| | - Ute A Hellmich
- Johannes Gutenberg-University, Department of Pharmacy and Biochemistry, Johann-Joachim-Becher-Weg 30, Mainz 55128, Germany; Centre for Biomolecular Magnetic Resonance (BMRZ), Goethe-University Frankfurt, Max von Laue-Str. 9, 60438 Frankfurt am Main, Germany
| | - Thomas Stockner
- Medical University of Vienna, Institute of Pharmacology, Waehringerstr. 13A, Vienna 1090, Austria.
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