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Blaimschein N, Hariharan P, Manioglu S, Guan L, Müller DJ. Substrate-binding guides individual melibiose permeases MelB to structurally soften and to destabilize cytoplasmic middle-loop C3. Structure 2023; 31:58-67.e4. [PMID: 36525976 PMCID: PMC9825662 DOI: 10.1016/j.str.2022.11.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Revised: 11/06/2022] [Accepted: 11/18/2022] [Indexed: 12/23/2022]
Abstract
The melibiose permease MelB is a well-studied Na+-coupled transporter of the major facilitator superfamily. However, the symport mechanism of galactosides and cations is still not fully understood, especially at structural levels. Here, we use single-molecule force spectroscopy to investigate substrate-induced structural changes of MelB from Salmonella typhimurium. In the absence of substrate, MelB equally populates two different states, from which one shows higher mechanical structural stability with additional stabilization of the cytoplasmic middle-loop C3. In the presence of either melibiose or a coupling Na+-cation, however, MelB increasingly populates the mechanically less stable state, which shows a destabilized middle-loop C3. In the presence of both substrate and co-substrate, this mechanically less stable state of MelB is predominant. Our findings describe how both substrates guide MelB transporters to populate two different mechanically stabilized states, and contribute mechanistic insights to the alternating-access action for the galactoside/cation symport catalyzed by MelB.
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Affiliation(s)
- Nina Blaimschein
- Department of Biosystems Science and Engineering, Eidgenössische Technische Hochschule (ETH) Zürich, 4058 Basel, Switzerland
| | - Parameswaran Hariharan
- Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Selen Manioglu
- Department of Biosystems Science and Engineering, Eidgenössische Technische Hochschule (ETH) Zürich, 4058 Basel, Switzerland
| | - Lan Guan
- Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA.
| | - Daniel J Müller
- Department of Biosystems Science and Engineering, Eidgenössische Technische Hochschule (ETH) Zürich, 4058 Basel, Switzerland.
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2
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Katsube S, Liang R, Amin A, Hariharan P, Guan L. Molecular basis for the cation selectivity of Salmonella typhimurium melibiose permease. J Mol Biol 2022; 434:167598. [DOI: 10.1016/j.jmb.2022.167598] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Revised: 04/14/2022] [Accepted: 04/14/2022] [Indexed: 12/23/2022]
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3
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Guan L, Hariharan P. X-ray crystallography reveals molecular recognition mechanism for sugar binding in a melibiose transporter MelB. Commun Biol 2021; 4:931. [PMID: 34341464 PMCID: PMC8329300 DOI: 10.1038/s42003-021-02462-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Accepted: 07/07/2021] [Indexed: 12/15/2022] Open
Abstract
Major facilitator superfamily_2 transporters are widely found from bacteria to mammals. The melibiose transporter MelB, which catalyzes melibiose symport with either Na+, Li+, or H+, is a prototype of the Na+-coupled MFS transporters, but its sugar recognition mechanism has been a long-unsolved puzzle. Two high-resolution X-ray crystal structures of a Salmonella typhimurium MelB mutant with a bound ligand, either nitrophenyl-α-d-galactoside or dodecyl-β-d-melibioside, were refined to a resolution of 3.05 or 3.15 Å, respectively. In the substrate-binding site, the interaction of both galactosyl moieties on the two ligands with MelBSt are virturally same, so the sugar specificity determinant pocket can be recognized, and hence the molecular recognition mechanism for sugar binding in MelB has been deciphered. The conserved cation-binding pocket is also proposed, which directly connects to the sugar specificity pocket. These key structural findings have laid a solid foundation for our understanding of the cooperative binding and symport mechanisms in Na+-coupled MFS transporters, including eukaryotic transporters such as MFSD2A. Guan and Hariharan report two crystal structures of melibiose transporter MelB in complex with substrate analogs, nitrophenyl-galactoside, and dodecyl-melibioside. Both structures revealed similar specific site for sugar recognition and resolved the cation-binding pocket, advancing the understanding of MelB and related transporters.
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Affiliation(s)
- Lan Guan
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, USA.
| | - Parameswaran Hariharan
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, USA
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Hariharan P, Guan L. Cooperative binding ensures the obligatory melibiose/Na+ cotransport in MelB. J Gen Physiol 2021; 153:212278. [PMID: 34110360 PMCID: PMC8200842 DOI: 10.1085/jgp.202012710] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2020] [Revised: 04/07/2021] [Accepted: 05/14/2021] [Indexed: 11/20/2022] Open
Abstract
MelB catalyzes the obligatory cotransport of melibiose with Na+, Li+, or H+. Crystal structure determination of the Salmonella typhimurium MelB (MelBSt) has revealed a typical major facilitator superfamily (MFS) fold at a periplasmic open conformation. Cooperative binding of Na+ and melibiose has been previously established. To determine why cotranslocation of sugar solute and cation is obligatory, we analyzed each binding in the thermodynamic cycle using three independent methods, including the determination of melting temperature by circular dichroism spectroscopy, heat capacity change (ΔCp), and regulatory phosphotransferase EIIAGlc binding with isothermal titration calorimetry (ITC). We found that MelBSt thermostability is increased by either substrate (Na+ or melibiose) and observed a cooperative effect of both substrates. ITC measurements showed that either binary formation yields a positive sign in the ΔCp, suggesting MelBSt hydration and a likely widening of the periplasmic cavity. Conversely, formation of a ternary complex yields negative values in ΔCp, suggesting MelBSt dehydration and cavity closure. Lastly, we observed that EIIAGlc, which has been suggested to trap MelBSt at an outward-open state, readily binds to the MelBSt apo state at an affinity similar to MelBSt/Na+. However, it has a suboptimal binding to the ternary state, implying that MelBSt in the ternary complex may be conformationally distant from the EIIAGlc-preferred outward-facing conformation. Our results consistently support the notion that binding of one substrate (Na+ or melibiose) favors MelBSt at open states, whereas the cooperative binding of both substrates triggers the alternating-access process, thus suggesting this conformational regulation could ensure the obligatory cotransport.
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Affiliation(s)
- Parameswaran Hariharan
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Lan Guan
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX
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5
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Hariharan P, Guan L. Thermodynamic cooperativity of cosubstrate binding and cation selectivity of Salmonella typhimurium MelB. J Gen Physiol 2017; 149:1029-1039. [PMID: 29054867 PMCID: PMC5677108 DOI: 10.1085/jgp.201711788] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2017] [Revised: 08/17/2017] [Accepted: 09/13/2017] [Indexed: 12/20/2022] Open
Abstract
The melibiose symporter MelB couples melibiose transport to that of cations such as Na+. Hariharan and Guan show that the binding of Na+ and melibiose is thermodynamically cooperative and that Na+ coupling is based on ion concentrations and competitive binding, but not ion selectivity. The Na+-coupled melibiose symporter MelB, which can also be coupled to H+ or Li+ transport, is a prototype for the glycoside-pentoside-hexuronide:cation symporter family. Although the 3-D x-ray crystal structure of Salmonella typhimurium MelB (MelBSt) has been determined, the symport mechanisms for the obligatory coupled transport are not well understood. Here, we apply isothermal titration calorimetry to determine the energetics of Na+ and melibiose binding to MelBSt, as well as protonation of this transporter. Studies of the thermodynamic cycle for the formation of the Na+–MelBSt–melibiose ternary complex at pH 7.45 reveal that the binding of Na+ and melibiose is cooperative. The binding affinity for one substrate (Na+ or melibiose) is increased by the presence of the other by about eightfold. The coupling free energies (ΔΔG) of either substrate binding are ∼5 kJ/mol, and binding of both substrates releases a free energy of ∼35 kJ/mol. Measurements of the Na+-binding enthalpy at three different pH values, including the pKa value of MelB, indicate that the binding of one Na+ displaces one H+ per MelBSt molecule. In addition, the absolute dissociation constants for Na+ and H+, determined by competitive binding, show that MelBSt is selective for H+ over Na+ by ∼1,000-fold at a pKa of 6.25. Thus, the Na+ coupling in MelBSt is based not on ion selectivity but on ion concentrations and competitive binding because of a much higher Na+ concentration under physiological conditions. Such a selectivity feature seems to be common for membrane transport proteins that can bind both H+ and Na+ at a common site.
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Affiliation(s)
- Parameswaran Hariharan
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Lan Guan
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX
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G117C MelB, a mutant melibiose permease with a changed conformational equilibrium. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:2508-16. [PMID: 21801712 DOI: 10.1016/j.bbamem.2011.07.017] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2011] [Revised: 06/17/2011] [Accepted: 07/05/2011] [Indexed: 11/22/2022]
Abstract
Replacement of the glycine at position 117 by a cysteine in the melibiose permease creates an interesting phenotype: while the mutant transporter shows still transport activity comparable to the wild type its pre steady-state kinetic properties are drastically altered. The transient charge displacements after substrate concentration jumps are strongly reduced and the fluorescence changes disappear. Together with its maintained transport activity this indicates that substrate translocation in G117C melibiose permease is not impaired but that the initial conformation of the mutant transporter differs from that of the wild type permease. A kinetic model for the G117C melibiose permease based on a rapid dynamic equilibrium of the substrate free transporter is proposed. Implications of the kinetic model for the transport mechanism of the wild type permease are discussed.
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7
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Meyer-Lipp K, Séry N, Ganea C, Basquin C, Fendler K, Leblanc G. The Inner Interhelix Loop 4–5 of the Melibiose Permease from Escherichia coli Takes Part in Conformational Changes after Sugar Binding. J Biol Chem 2006; 281:25882-92. [PMID: 16822867 DOI: 10.1074/jbc.m601259200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cytoplasmic loop 4-5 of the melibiose permease from Escherichia coli is essential for the process of Na+-sugar translocation (Abdel-Dayem, M., Basquin, C., Pourcher, T., Cordat, E., and Leblanc, G. (2003) J. Biol. Chem. 278, 1518-1524). In the present report, we analyze functional consequences of mutating each of the three acidic amino acids in this loop into cysteines. Among the mutants, only the E142C substitution impairs selectively Na+-sugar translocation. Because R141C has a similar defect, we investigated these two mutants in more detail. Liposomes containing purified mutated melibiose permease were adsorbed onto a solid supported lipid membrane, and transient electrical currents resulting from different substrate concentration jumps were recorded. The currents evoked by a melibiose concentration jump in the presence of Na+, previously assigned to an electrogenic conformational transition (Meyer-Lipp, K., Ganea, C., Pourcher, T., Leblanc, G., and Fendler, K. (2004) Biochemistry 43, 12606-12613), were much smaller for the two mutants than the corresponding signals in cysteineless MelB. Furthermore, in R141C the stimulating effect of melibiose on Na+ affinity was lost. Finally, whereas tryptophan fluorescence spectroscopy revealed impaired conformational changes upon melibiose binding in the mutants, fluorescence resonance energy transfer measurements indicated that the mutants still show cooperative modification of their sugar binding sites by Na+. These data suggest that: 1) loop 4-5 contributes to the coordinated interactions between the ion and sugar binding sites; 2) it participates in an electrogenic conformational transition after melibiose binding that is essential for the subsequent obligatory coupled translocation of substrates. A two-step mechanism for substrate translocation in the melibiose permease is suggested.
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Affiliation(s)
- Kerstin Meyer-Lipp
- Max Planck Institute of Biophysics, Max-von-Laue-Strasse 3, 60438 Frankfurt/M, Germany
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Ding PZ. Loop X/XI, the largest cytoplasmic loop in the membrane-bound melibiose carrier of Escherichia coli, is a functional re-entrant loop. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2004; 1660:106-17. [PMID: 14757226 DOI: 10.1016/j.bbamem.2003.11.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The melibiose carrier of Escherichia coli is a membrane-bound sugar-cation cotransporter consisting of 12 transmembrane helices connected by cytoplasmic and periplasmic loops, with both N- and C-terminus on the cytoplasmic side. Using a functional cysteine-less carrier, cysteine was substituted individually for residues 347-378 that comprise the largest cytoplasmic loop X/XI. The majority of the cysteine mutants have good protein expression levels. The cysteine mutants were studied for their transport activities, and the inhibitory effects of two sulfhydryl reagents, PCMBS (7-A long) and BM (29-A long). Cysteine substitution resulted in substantial loss of transport in 12 mutants. While PCMBS caused significant inhibition in only two mutants, T373C and V376C, from the periplasmic side (in a substrate-protective manner), more extensive inhibition pattern was observed from the cytoplasmic side, in seven mutants: V353C, Y358C, V371C, Q372C, T373C, V376C and G378C, suggesting that these residues are along the sugar pathway in the aqueous channel, close to the cytoplasmic side. Furthermore, the inhibitory effect of BM on the inside-out vesicles of the above mutants was clearly less than that of PCMBS, suggesting channel space limitation to large molecules, consistent with those residues being inside the channel. Three second-site revertants (A350C/F268L, A350C/I22S, and A350C/I22N) were selected. They may suggest proximities between loop X/XI and helices I and VIII, in agreement with a re-entrant loop structure. Self thiol cross-linkings of the cysteine mutants on loop X/XI failed to form dimers, suggesting that most of the loop is not surface-exposed from cytoplasmic side. Together, these results strongly indicated a functional re-entrant loop mechanistically important in Na+-coupled transporters.
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Affiliation(s)
- Ping Z Ding
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA.
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9
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Abdel-Dayem M, Basquin C, Pourcher T, Cordat E, Leblanc G. Cytoplasmic loop connecting helices IV and V of the melibiose permease from Escherichia coli is involved in the process of Na+-coupled sugar translocation. J Biol Chem 2003; 278:1518-24. [PMID: 12421811 DOI: 10.1074/jbc.m210053200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous photolabeling and limited proteolysis studies suggested that one of the four basic residues (Arg-141) of the N-terminal cytoplasmic loop connecting helices IV and V (loop 4-5) of the melibiose permease (MelB) from Escherichia coli has a potential role in its symport function (Ambroise, Y., Leblanc, G., and Rousseau, B. (2000) Biochemistry 39, 1338-1345). A mutagenesis study of Arg-141 and of the other three basic residues of loop 4-5 was undertaken to further examine this hypothesis. Cys replacement analysis indicated that Arg-141 and Arg-149, but not Lys-138 and Arg-139, are essential for MelB transport activity. Replacement of Arg-141 by neutral residues (Cys or Gln) inactivated transport and energy-independent carrier-mediated flows of substrates (counterflow, efflux), whereas it had a limited effect on co-substrate binding. R141C sugar transport was partially rescued on reintroducing a positive charge with a charged and permeant thiol reagent. Whereas R149C was completely inactive, R149K and R149Q remained functional. Strikingly, introduction of an additional mutation in the C-terminal helix X (Gly for Val-343) of R149C restored sugar transport. Impermeant thiol reagents inhibited R149C/V343G transport activity in right-side-out membrane vesicles and prevented sugar binding in a sugar-protected manner. All these data suggest that MelB loop 4-5 is close to the sugar binding site and that the charged residue Arg-141 is involved in the reaction of co-substrate translocation or substrate release in the inner compartment.
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Affiliation(s)
- Manal Abdel-Dayem
- Laboratoire de Physiologie des Membranes Cellulaires, Université de Nice Sophia-Antipolis and CNRS UMR 6078, Commissariat à l'Energie Atomique (LRC-CEA 16V), Villefranche sur mer, 06230 France
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10
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Ding PZ, Wilson TH. The proximity between helix I and helix XI in the melibiose carrier of Escherichia coli as determined by cross-linking. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1514:230-8. [PMID: 11557023 DOI: 10.1016/s0005-2736(01)00385-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The melibiose carrier of Escherichia coli is a transmembrane protein that comprises 12 transmembrane helices connected by periplasmic and cytoplasmic loops, with both the N- and C-termini located on the cytoplasmic side. Our previous studies of second-site revertants suggested proximity between several helices, including helices XI and I. In this study, we constructed six double cysteine mutants, each having one cysteine in helix I and the other in helix XI: three mutants, K18C/S380C, D19C/S380C, and F20C/S380C, have their cysteine pairs near the cytoplasmic side of the carrier, and the other three, T34C/G395C, D35C/G395C, and V36C/G395C, have their cysteine pairs near the periplasmic side. In the absence of substrate, disulfide formations catalyzed by iodine and copper-(1,10-phenanthroline)(3) indicate that helix I and helix XI are in immediate proximity to each other on the periplasmic side but not on the cytoplasmic side, as shown by protease cleavage analyses. We infer that the two helices are tilted with respect to each other, with the periplasmic sides in close proximity.
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Affiliation(s)
- P Z Ding
- Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
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11
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Ding PZ, Wilson TH. The effect of modifications of the charged residues in the transmembrane helices on the transport activity of the melibiose carrier of Escherichia coli. Biochem Biophys Res Commun 2001; 285:348-54. [PMID: 11444849 DOI: 10.1006/bbrc.2001.5200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The melibiose transport carrier of Escherichia coli (coded by melB gene) is a cotransport system which couples the transport of a-galactosides to protons, sodium, or lithium ions. The charged amino acid residues in membrane-spanning helices are of considerable interest because many of them have important function in substrate recognition. In most cases changing these charged residue to an uncharged residue (cysteine) results in total loss of activity. In this communication we describe experiments in which the cysteine substitution for a charged residue was chemically changed by sulfhydryl reagents (MTSEA and MTSET to restore a positive charge and MTSES a negative charge) or by iodoacetic acid or through oxidation by hydrogen peroxide so as to regain the original negative charge. In two cases (D55C and D124C) the reconstructed negative charges via the oxidation of the thiol to the sulfinic and/or sulfonic acid resulted in partial recovery of transport: D55C up to 27% of the normal and D124C up to 4% of the normal in melibiose accumulation; D55C up to 36% of the normal and D124 up to 4.5% of the normal in downhill transport. Sulfhydryl reagents and iodoacetic acid failed to recover transport in all cases. We infer that the configurations of the charges as well as the structure of the side chains that carry them are critical in the maintenance of the transport.
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Affiliation(s)
- P Z Ding
- Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
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12
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Ding PZ, Wilson TH. Physiological evidence for an interaction between helix XI and helices I, II, and V in the melibiose carrier of Escherichia coli. Biochem Biophys Res Commun 2000; 268:409-13. [PMID: 10679218 DOI: 10.1006/bbrc.2000.2149] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In a previous study 23 residues in helix XI of the cysteine-less melibiose carrier were changed individually to cysteine. Several of these cysteine mutants (K377C, A383C, F385C, L391C, G395C) had low transport activity and they were white on melibiose MacConkey fermentation plates. After several days of incubation of these white clones on melibiose MacConkey plates a rare red mutant appeared. The plasmid DNA was then isolated and sequenced. The two second site revertants from K377C were I22S and D59A. This change of aspartic acid to a neutral residue suggests that physiologically there is an interaction between K377 and D59 (possibly a salt bridge). The revertants from A383C were in positions 20 (F20L) and 22 (I22S and I22N). Revertants of F385C were intrahelical changes (I387M and A388G) and a change in C-terminal loop (R441C). Revertants of L391C were in helix I (I22N, I22T and D19E) and helix V (A152S). Revertants of G395C were in helix I (D19E and I22N). We suggest that there is an interaction between helix XI and helices I, II, and V and proximity between these helices.
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Affiliation(s)
- P Z Ding
- Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
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13
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Hirayama BA, Loo DD, Wright EM. Cation effects on protein conformation and transport in the Na+/glucose cotransporter. J Biol Chem 1997; 272:2110-5. [PMID: 8999910 DOI: 10.1074/jbc.272.4.2110] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Cation-driven cotransporters are essential membrane proteins in procaryotes and eucaryotes, which use the energy of the transmembrane electrochemical gradient to drive transport of a substrate against its concentration gradient. Do they share a common mechanism? Cation selectivity of the rabbit isoform of the Na+/glucose cotransporter (SGLT1) was examined using the twoelectrode voltage clamp and the Xenopus oocyte expression system. The effect of H+, Li+, and Na+ on kinetics of SGLT1 was compared to the effects of these cations on the bacterial melibiose. In SGLT1, substitution of H+ or Li+ for Na+ caused a kinetic penalty in that the apparent affinity for sugar (K0.5sugar) decreased by an order of magnitude or more (from 0.2 to 30 mM) depending on the membrane potential and cation. The effect of the cation on the K0.5sugar/V profiles was independent of the sugar for glucose and alpha-methyl-beta-D-glucose; this profile was maintained for galactose in Li+ and Na+, but was 2 orders of magnitude higher in H+, but the Imax for glucose, galactose, and alpha-methyl-beta-D-glucose in a given cation were identical. Li+ supported a lower maximal rate of transport (Imax) than Na+ (approximately 80% of ImaxNa), while the Imax in H+ was higher than Na+ (>/=180% of ImaxNa). Our interpretation of these results and simulations using a six-state mathematical model, are as follows. 1) Binding of the cation causes a conformational change in the sugar binding pocket, the exact conformation being determined by the specific cation. 2) Once the sugar is bound, it is transported at a characteristic rate determined by the cation. 3) Mathematical simulations suggest that the largest contribution to the kinetic variability of both cation and sugar transport is associated with cation binding. Similarity to the effects of cation substitution in MelB suggests that the mechanism of energy coupling has been evolutionarily conserved.
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Affiliation(s)
- B A Hirayama
- Department of Physiology, UCLA School of Medicine, Los Angeles, California 90095-1751, USA.
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14
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Mus-Veteau I, Pourcher T, Leblanc G. Melibiose permease of Escherichia coli: substrate-induced conformational changes monitored by tryptophan fluorescence spectroscopy. Biochemistry 1995; 34:6775-83. [PMID: 7756309 DOI: 10.1021/bi00020a024] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Tryptophan fluorescence spectroscopy has been used to investigate the effects of sugars and coupling cations (H+, Na+, or Li+) on the conformational properties of purified melibiose permease after reconstitution in liposomes. Melibiose permease emission fluorescence is selectively enhanced by sugars, which serve as substrates for the symport reaction, alpha-galactosides producing larger variations (13-17%) than beta-galactosides (7%). Moreover, the sugar-dependent fluorescence increase is specifically potentiated by NaCl and LiCl (5-7 times), which are well-established activators of sugar binding and transport by the permease. The potentiation effect is greater in the presence of LiCl than NaCl. On their own, sodium and lithium ions produce quenching of the fluorescence signal (2%). Evidence suggesting that sugars and cations compete for their respective binding sites is also given. Both the sugar-induced fluorescence variation and the NaCl(or LiCl)-dependent potentiation effect exhibit saturation kinetics. In each ionic condition, the half-maximal fluorescence change is found at a sugar concentration corresponding to the sugar-binding constant. Also, half-maximal potentiation of the fluorescence change by sodium or lithium occurs at a concentration comparable to the activation constant of sugar binding by each ion. The sugar- and ion-dependent fluorescence variations still take place after selective inactivation of the permease substrate translocation capacity by N-ethylmaleimide. Taken together, the data suggest that the changes in permease fluorescence reflect conformational changes occurring upon the formation of ternary sugar/cation/permease complexes.
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Affiliation(s)
- I Mus-Veteau
- Laboratoire J. Maetz, Departement de Biologie Cellulaire et Moleculaire du Commissariat à l'Energie Atomique, Villefranche sur mer, France
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15
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Zani M, Pourcher T, Leblanc G. Mutation of polar and charged residues in the hydrophobic NH2-terminal domains of the melibiose permease of Escherichia coli. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)31473-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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16
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Affiliation(s)
- B Poolman
- Department of Microbiology, University of Groningen, Haren, The Netherlands
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17
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Pourcher T, Zani M, Leblanc G. Mutagenesis of acidic residues in putative membrane-spanning segments of the melibiose permease of Escherichia coli. I. Effect on Na(+)-dependent transport and binding properties. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53679-6] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Mutagenesis of acidic residues in putative membrane-spanning segments of the melibiose permease of Escherichia coli. II. Effect on cationic selectivity and coupling properties. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53680-2] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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19
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Pourcher T, Bassilana M, Sarkar HK, Kaback HR, Leblanc G. Melibiose permease of Escherichia coli: mutation of histidine-94 alters expression and stability rather than catalytic activity. Biochemistry 1992; 31:5225-31. [PMID: 1606146 DOI: 10.1021/bi00137a018] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Previous studies utilizing site-directed mutagenesis [Pourcher et al. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 468-472] indicate that out of seven histidinyl residues in the melibiose (mel) permease of Escherichia coli, only His94 is important. The role of His94 has now been investigated by replacing the residue with Asn, Gln, or Arg. Cells expressing mel permease with Asn94 or Gln94 retain 30% or 20% of wild-type activity, respectively, and surprisingly, immunological assays demonstrate that diminished transport activity is due to a proportional reduction in the amount of permease in the membrane. Moreover, kinetic analyses of transport and ligand binding studies with right-side-out membrane vesicles indicate that both substrate recognition and turnover (kcat) are comparable in the mutant permeases and the wild-type. Mel permease with Arg in place of His94 also binds ligand and catalyzes sugar accumulation, but only when the cells are grown at 30 degrees C, and evidence is presented that Arg94 permease is inactivated at 37 degrees C. Finally, labeling studies demonstrate that expression and/or insertion of the permease, but not degradation, is strongly dependent on the amino acid present at position 94 and temperature. The findings indicate that an imidazole group at position 94 is required for proper insertion and stability of mel permease, but not for transport activity per se. Since replacement of the other six histidinyl residues in mel permease with Arg has little or no effect on transport activity, it is concluded that histidinyl residues do not play a direct role in the mechanism of this secondary transport protein.
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Affiliation(s)
- T Pourcher
- Laboratoire J. Maetz, Département de Biologie Cellulaire et Moléculaire du Commissariat à l'Energie Atomique, Villefranche sur mer, France
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20
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Sugar—Cation Symport Systems in Bacteria. ACTA ACUST UNITED AC 1992. [DOI: 10.1016/s0074-7696(08)62676-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/21/2023]
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21
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Chapter 2 Chemiosmotic systems and the basic principles of cell energetics. MOLECULAR MECHANISMS IN BIOENERGETICS 1992. [DOI: 10.1016/s0167-7306(08)60170-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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22
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Skulachev VP. Chemiosmotic systems in bioenergetics: H(+)-cycles and Na(+)-cycles. Biosci Rep 1991; 11:387-441; discussion 441-4. [PMID: 1668527 DOI: 10.1007/bf01130214] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The development of membrane bioenergetic studies during the last 25 years has clearly demonstrated the validity of the Mitchellian chemiosmotic H+ cycle concept. The circulation of H+ ions was shown to couple respiration-dependent or light-dependent energy-releasing reactions to ATP formation and performance of other types of membrane-linked work in mitochondria, chloroplasts, some bacteria, tonoplasts, secretory granules and plant and fungal outer cell membranes. A concrete version of the direct chemiosmotic mechanism, in which H+ potential formation is a simple consequence of the chemistry of the energy-releasing reaction, is already proved for the photosynthetic reaction centre complexes. Recent progress in the studies on chemiosmotic systems has made it possible to extend the coupling-ion principle to an ion other than H+. It was found that, in certain bacteria, as well as in the outer membrane of the animal cell, Na+ effectively substitutes for H+ as the coupling ion (the chemiosmotic Na+ cycle). A precedent is set when the Na+ cycle appears to be the only mechanism of energy production in the bacterial cell. In the more typical case, however, the H+ and Na+ cycles coexist in one and the same membrane (bacteria) or in two different membranes of one and the same cell (animals). The sets of delta mu H+ and delta mu Na+ generators as well as delta mu H+ and delta mu Na+ consumers found in different types of biomembranes, are listed and discussed.
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Affiliation(s)
- V P Skulachev
- Department of Bioenergetics, A. N. Belozersky Laboratory of Molecular Biology and Bioorganic Chemistry, Moscow State University, USSR
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23
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Dibrov PA. The role of sodium ion transport in Escherichia coli energetics. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1056:209-24. [PMID: 1848102 DOI: 10.1016/s0005-2728(05)80052-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- P A Dibrov
- Department of Bioenergetics, A.N. Belozersky Laboratory of Molecular Biology and Bioorganic Chemistry, Moscow State University, U.S.S.R
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24
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Abstract
The cell membranes of various bacteria contain proton-linked transport systems for D-xylose, L-arabinose, D-galactose, D-glucose, L-rhamnose, L-fucose, lactose, and melibiose. The melibiose transporter of E. coli is linked to both Na+ and H+ translocation. The substrate and inhibitor specificities of the monosaccharide transporters are described. By locating, cloning, and sequencing the genes encoding the sugar/H+ transporters in E. coli, the primary sequences of the transport proteins have been deduced. Those for xylose/H+, arabinose/H+, and galactose/H+ transport are homologous to each other. Furthermore, they are just as similar to the primary sequences of the following: glucose transport proteins found in a Cyanobacterium, yeast, alga, rat, mouse, and man; proteins for transport of galactose, lactose, or maltose in species of yeast; and to a developmentally regulated protein of Leishmania for which a function is not yet established. Some of these proteins catalyze facilitated diffusion of the sugar without cation transport. From the alignments of the homologous amino acid sequences, predictions of common structural features can be made: there are likely to be twelve membrane-spanning alpha-helices, possibly in two groups of six; there is a central hydrophilic region, probably comprised largely of alpha-helix; the highly conserved amino acid residues (40-50 out of 472-522 total) form discrete patterns or motifs throughout the proteins that are presumably critical for substrate recognition and the molecular mechanism of transport. Some of these features are found also in other transport proteins for citrate, tetracycline, lactose, or melibiose, the primary sequences of which are not similar to each other or to the homologous series of transporters. The glucose/Na+ transporter of rabbit and man is different in primary sequence to all the other sugar transporters characterized, but it is homologous to the proline/Na+ transporter of E. coli, and there is evidence for its structural similarity to glucose/H+ transporters in Plants. In vivo and in vitro mutagenesis of the lactose/H+ and melibiose/Na+ (H+) transporters of E. coli has identified individual amino acid residues alterations of which affect sugar and/or cation recognition and parameters of transport. Most of the bacterial transport proteins have been identified and the lactose/H+ transporter has been purified. The directions of future investigations are discussed.
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Affiliation(s)
- P J Henderson
- Department of Biochemistry, University of Cambridge, United Kingdom
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25
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Pourcher T, Bassilana M, Sarkar HK, Kaback HR, Leblanc G. The melibiose/Na+ symporter of Escherichia coli: kinetic and molecular properties. Philos Trans R Soc Lond B Biol Sci 1990; 326:411-23. [PMID: 1970646 DOI: 10.1098/rstb.1990.0021] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The role of the co-transported cation in the coupling mechanism of the melibiose permease of Escherichia coli has been investigated by analysing its sugar-binding activity, facilitated diffusion reactions and energy-dependent transport reactions catalysed by the carrier functioning either as an H+, Na+ or Li(+)-sugar symporter. The results suggest that the coupling cation not only acts as an activator for sugar-binding on the carrier but also regulates the rate of dissociation of the co-substrates in the cytoplasm by controlling the stability of the ternary complex cation-sugar-carrier facing the cell interior. Furthermore, there is some evidence that the membrane potential enhances the rate of symport activity by increasing the rate of dissociation of the co-substrates from the carrier in the cellular compartment. Identification of the melibiose permease as a membrane protein of 39 kDa by using a T7 RNA polymerase/promoter expression system is described. Site-directed mutagenesis has been used to replace individual carrier histidine residues by arginine to probe the functional contribution of each of the seven histidine residues to the symport mechanism. Only substitution of arginine for His94 greatly interferes with the carrier function. It is finally shown that mutations affecting the glutamate residue in position 361 inactivate translocation of the co-substrates but not their recognition by the permease.
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Affiliation(s)
- T Pourcher
- Laboratoire J. Maetz, Departement de Biologie du CEA, Villefranche sur Mer, France
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26
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Glaser R. The influence of membrane electric field on cellular functions. SPRINGER SERIES IN BIOPHYSICS 1990. [DOI: 10.1007/978-3-642-74471-6_10] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
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27
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Bassilana M, Pourcher T, Leblanc G. Melibiose permease of Escherichia coli. Characteristics of co-substrates release during facilitated diffusion reactions. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(19)81568-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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28
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Bassilana M, Pourcher T, Leblanc G. Facilitated diffusion properties of melibiose permease in Escherichia coli membrane vesicles. Release of co-substrates is rate limiting for permease cycling. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(18)45463-4] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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29
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Damiano-Forano E, Bassilana M, Leblanc G. Sugar binding properties of the melibiose permease in Escherichia coli membrane vesicles. Effects of Na+ and H+ concentrations. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(19)62700-6] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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