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Jaunet-Lahary T, Shimamura T, Hayashi M, Nomura N, Hirasawa K, Shimizu T, Yamashita M, Tsutsumi N, Suehiro Y, Kojima K, Sudo Y, Tamura T, Iwanari H, Hamakubo T, Iwata S, Okazaki KI, Hirai T, Yamashita A. Structure and mechanism of oxalate transporter OxlT in an oxalate-degrading bacterium in the gut microbiota. Nat Commun 2023; 14:1730. [PMID: 37012268 PMCID: PMC10070484 DOI: 10.1038/s41467-023-36883-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Accepted: 02/20/2023] [Indexed: 04/05/2023] Open
Abstract
An oxalate-degrading bacterium in the gut microbiota absorbs food-derived oxalate to use this as a carbon and energy source, thereby reducing the risk of kidney stone formation in host animals. The bacterial oxalate transporter OxlT selectively uptakes oxalate from the gut to bacterial cells with a strict discrimination from other nutrient carboxylates. Here, we present crystal structures of oxalate-bound and ligand-free OxlT in two distinct conformations, occluded and outward-facing states. The ligand-binding pocket contains basic residues that form salt bridges with oxalate while preventing the conformational switch to the occluded state without an acidic substrate. The occluded pocket can accommodate oxalate but not larger dicarboxylates, such as metabolic intermediates. The permeation pathways from the pocket are completely blocked by extensive interdomain interactions, which can be opened solely by a flip of a single side chain neighbouring the substrate. This study shows the structural basis underlying metabolic interactions enabling favourable symbiosis.
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Affiliation(s)
- Titouan Jaunet-Lahary
- Research Center for Computational Science, Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, 444-8585, Japan
| | - Tatsuro Shimamura
- Graduate School of Medicine, Kyoto University, Kyoto, 606-8501, Japan.
| | - Masahiro Hayashi
- Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan
| | - Norimichi Nomura
- Graduate School of Medicine, Kyoto University, Kyoto, 606-8501, Japan
| | - Kouta Hirasawa
- Graduate School of Medicine, Kyoto University, Kyoto, 606-8501, Japan
| | | | | | - Naotaka Tsutsumi
- Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan
- School of Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan
| | - Yuta Suehiro
- School of Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan
| | - Keiichi Kojima
- Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan
| | - Yuki Sudo
- Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan
| | - Takashi Tamura
- Graduate School of Environmental and Life Sciences, Okayama University, Okayama, 700-8530, Japan
| | - Hiroko Iwanari
- Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, 153-8904, Japan
| | - Takao Hamakubo
- Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, 153-8904, Japan
| | - So Iwata
- Graduate School of Medicine, Kyoto University, Kyoto, 606-8501, Japan
| | - Kei-Ichi Okazaki
- Research Center for Computational Science, Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, 444-8585, Japan.
| | | | - Atsuko Yamashita
- Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan.
- RIKEN SPring-8 Center, Sayo, 679-5148, Japan.
- School of Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan.
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Iyalomhe O, Herrick DZ, Cafiso DS, Maloney PC. Closure of the cytoplasmic gate formed by TM5 and TM11 during transport in the oxalate/formate exchanger from Oxalobacter formigenes. Biochemistry 2014; 53:7735-44. [PMID: 25409483 PMCID: PMC4270380 DOI: 10.1021/bi5012173] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
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OxlT, the oxalate/formate exchanger
of Oxalobacter
formigenes, is a member of the major facilitator superfamily
of transporters. In the present work, substrate (oxalate) was found
to enhance the reactivity of the cysteine mutant S336C on the cytoplasmic
end of helix 11 to methanethiosulfonate ethyl carboxylate. In addition,
S336C is found to spontaneously cross-link to S143C in TM5 in either
native or reconstituted membranes under conditions that support transport.
Continuous wave EPR measurements are consistent with this result and
indicate that positions 143 and 336 are in close proximity in the
presence of substrate. These two residues are localized within helix
interacting GxxxG-like motifs (G140LASG144 and
S336DIFG340) at the cytoplasmic poles of TM5
and TM11. Pulse EPR measurements were used to determine distances
and distance distributions across the cytoplasmic or periplasmic ends
of OxlT and were compared with the predictions of an inside-open homology
model. The data indicate that a significant population of transporter
is in an outside-open configuration in the presence of substrate;
however, each end of the transporter exhibits significant conformational
heterogeneity, where both inside-open and outside-open configurations
are present. These data indicate that TM5 and TM11, which form part
of the transport pathway, transiently close during transport and that
there is a conformational equilibrium between inside-open and outside-open
states of OxlT in the presence of substrate.
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Affiliation(s)
- Osigbemhe Iyalomhe
- Department of Physiology, The Johns Hopkins University, School of Medicine , 725 North Wolfe Street, Baltimore, Maryland 21205, United States
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Alanine scanning mutagenesis of a high-affinity nitrate transporter highlights the requirement for glycine and asparagine residues in the two nitrate signature motifs. Biochem J 2012; 447:35-42. [DOI: 10.1042/bj20120631] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Common to all of the nitrate nitrite porter family are two conserved motifs in transmembrane helices 5 and 11 termed NS (nitrate signature) 1 and NS2. Although perfectly conserved substrate-interacting arginine residues have been described in transmembrane helices 2 and 8, the role of NSs has not been investigated. In the present study, a combination of structural modelling of NrtA (nitrate transporter from Aspergillus nidulans) with alanine scanning mutagenesis of residues within and around the NSs has been used to shed light on the probable role of conserved residues in the NSs. Models show that Asn168 in NS1 and Asn459 in NS2 are positioned approximately midway within the protein at the central pivot point in close proximity to the substrate-binding residues Arg368 and Arg87 respectively, which lie offset from the pivot point towards the cytoplasmic face. The Asn168/Arg368 and Asn459/Arg87 residue pairs are relatively widely separated on opposite sides of the probable substrate translocation pore. The results of the present study demonstrate the critical structural contribution of several glycine residues in each NS at sites of close helix packing. Given the relative locations of Asn168/Arg368 and Asn459/Arg87 pairs, the validity of the models and possible role of the NSs together with the substrate-binding arginine residues are discussed.
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Kasahara T, Shimogawara K, Kasahara M. Crucial effects of amino acid side chain length in transmembrane segment 5 on substrate affinity in yeast glucose transporter Hxt7. Biochemistry 2011; 50:8674-81. [PMID: 21892826 DOI: 10.1021/bi200958s] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
We previously identified Asp(340) in transmembrane segment 7 (TM7) as a key determinant of substrate affinity in Hxt7, a high-affinity facilitative glucose transporter of Saccharomyces cerevisiae. To gain further insight into the structural basis of substrate recognition by Hxt7, we performed cysteine-scanning mutagenesis of 21 residues in TM5 of a Cys-less form of Hxt7. Four residues were sensitive to Cys replacement, among which Gln(209) was found to be essential for high-affinity glucose transport activity. The 17 remaining sites were examined further for the accessibility of cysteine to the hydrophilic sulfhydryl reagent p-chloromercuribenzenesulfonate (pCMBS). Among the Cys mutants, T213C was the only one whose transport activity was completely inhibited by 0.5 mM pCMBS. Moreover, this mutant was protected from pCMBS inhibition by the substrate d-glucose and by 2-deoxy-D-glucose but not by L-glucose, indicating that Thr(213) is situated at or close to a substrate recognition site. The functional role of Thr(213) was further examined with its replacement with each of the other 19 amino acids in wild-type Hxt7. Such replacement generated seven functional transporters with various affinities for glucose. Only three mutants, those with Val, Cys, and Ser at position 213, exhibited high-affinity glucose transport activity. All of these residues possess a side chain length similar to that of Thr, indicating that side chain length at this position is a key determinant of substrate affinity. A working homology model of Hxt7 indicated that Gln(209) and Thr(213) face the central cavity and that Thr(213) is located within van der Waals distance of Asp(340) (TM7).
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Affiliation(s)
- Toshiko Kasahara
- Laboratory of Biophysics, School of Medicine, Teikyo University, Hachioji, Tokyo 192-0395, Japan.
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Riegelhaupt PM, Frame IJ, Akabas MH. Transmembrane segment 11 appears to line the purine permeation pathway of the Plasmodium falciparum equilibrative nucleoside transporter 1 (PfENT1). J Biol Chem 2010; 285:17001-10. [PMID: 20335165 DOI: 10.1074/jbc.m110.115758] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Purine transport is essential for malaria parasites to grow because they lack the enzymes necessary for de novo purine biosynthesis. The Plasmodium falciparum Equilibrative Nucleoside Transporter 1 (PfENT1) is a member of the equilibrative nucleoside transporter (ENT) gene family. PfENT1 is a primary purine transport pathway across the P. falciparum plasma membrane because PfENT1 knock-out parasites are not viable at physiologic extracellular purine concentrations. Topology predictions and experimental data indicate that ENT family members have eleven transmembrane (TM) segments although their tertiary structure is unknown. In the current work, we showed that a naturally occurring polymorphism, F394L, in TM11 affects transport substrate K(m). We investigated the structure and function of the TM11 segment using the substituted cysteine accessibility method. We showed that mutation to Cys of two highly conserved glycine residues in a GXXXG motif significantly reduces PfENT1 protein expression levels. We speculate that the conserved TM11 GXXXG glycines may be critical for folding and/or assembly. Small, cysteine-specific methanethiosulfonate (MTS) reagents reacted with four TM11 Cys substitution mutants, L393C, I397C, T400C, and Y403C. Larger MTS reagents do not react with the more cytoplasmic positions. Hypoxanthine, a transported substrate, protected L393C, I397C, and T400C from covalent modification by the MTS reagents. Plotted on an alpha-helical wheel, Leu-393, Ile-397, and Thr-400 lie on one face of the helix in a 60 degrees arc suggesting that TM11 is largely alpha helical. We infer that they line a water-accessible surface, possibly the purine permeation pathway. These results advance our understanding of the ENT structure.
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Affiliation(s)
- Paul M Riegelhaupt
- Department of Physiology and Biophysics, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, USA
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Structural and functional importance of transmembrane domain 3 (TM3) in the aspartate:alanine antiporter AspT: topology and function of the residues of TM3 and oligomerization of AspT. J Bacteriol 2009; 191:2122-32. [PMID: 19181816 DOI: 10.1128/jb.00830-08] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
AspT, the aspartate:alanine antiporter of Tetragenococcus halophilus, a membrane protein of 543 amino acids with 10 putative transmembrane (TM) helices, is the prototype of the aspartate:alanine exchanger (AAE) family of transporters. Because TM3 (isoleucine 64 to methionine 85) has many amino acid residues that are conserved among members of the AAE family and because TM3 contains two charged residues and four polar residues, it is thought to be located near (or to form part of) the substrate translocation pathway that includes the binding site for the substrates. To elucidate the role of TM3 in the transport process, we carried out cysteine-scanning mutagenesis. The substitutions of tyrosine 75 and serine 84 had the strongest inhibitory effects on transport (initial rates of l-aspartate transport were below 15% of the rate for cysteine-less AspT). Considerable but less-marked effects were observed upon the replacement of methionine 70, phenylalanine 71, glycine 74, arginine 76, serine 83, and methionine 85 (initial rates between 15% and 30% of the rate for cysteine-less AspT). Introduced cysteine residues at the cytoplasmic half of TM3 could be labeled with Oregon green maleimide (OGM), whereas cysteines close to the periplasmic half (residues 64 to 75) were not labeled. These results suggest that TM3 has a hydrophobic core on the periplasmic half and that hydrophilic residues on the cytoplasmic half of TM3 participate in the formation of an aqueous cavity in membranes. Furthermore, the presence of l-aspartate protected the cysteine introduced at glycine 62 against a reaction with OGM. In contrast, l-aspartate stimulated the reactivity of the cysteine introduced at proline 79 with OGM. These results demonstrate that TM3 undergoes l-aspartate-induced conformational alterations. In addition, nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses and a glutaraldehyde cross-linking assay suggest that functional AspT forms homo-oligomers as a functional unit.
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