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Zhang Q, Padayatti PS, Leung JH. Proton-Translocating Nicotinamide Nucleotide Transhydrogenase: A Structural Perspective. Front Physiol 2017; 8:1089. [PMID: 29312000 PMCID: PMC5742237 DOI: 10.3389/fphys.2017.01089] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Accepted: 12/11/2017] [Indexed: 01/07/2023] Open
Abstract
Nicotinamide nucleotide transhydrogenase (TH) is an enzyme complex in animal mitochondria and bacteria that utilizes the electrochemical proton gradient across membranes to drive the production of NADPH. The enzyme plays an important role in maintaining the redox balance of cells with implications in aging and a number of human diseases. TH exists as a homodimer with each protomer containing a proton-translocating transmembrane domain and two soluble nucleotide binding domains that mediate hydride transfer between NAD(H) and NADP(H). The three-domain architecture of TH is conserved across species but polypeptide composition differs substantially. The complex domain coupling mechanism of TH is not fully understood despite extensive biochemical and structural characterizations. Herein the progress is reviewed, focusing mainly on structural findings from 3D crystallization of isolated soluble domains and more recently of the transmembrane domain and the holo-enzyme from Thermus thermophilus. A structural perspective and impeding challenges in further elucidating the mechanism of TH are discussed.
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Affiliation(s)
- Qinghai Zhang
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, United States
| | - Pius S Padayatti
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, United States
| | - Josephine H Leung
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, United States
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2
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Jackson JB, Leung JH, Stout CD, Schurig-Briccio LA, Gennis RB. Review and Hypothesis. New insights into the reaction mechanism of transhydrogenase: Swivelling the dIII component may gate the proton channel. FEBS Lett 2015; 589:2027-33. [PMID: 26143375 DOI: 10.1016/j.febslet.2015.06.027] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Revised: 06/17/2015] [Accepted: 06/17/2015] [Indexed: 11/26/2022]
Abstract
The membrane protein transhydrogenase in animal mitochondria and bacteria couples reduction of NADP⁺ by NADH to proton translocation. Recent X-ray data on Thermus thermophilus transhydrogenase indicate a significant difference in the orientations of the two dIII components of the enzyme dimer (Leung et al., 2015). The character of the orientation change, and a review of information on the kinetics and thermodynamics of transhydrogenase, indicate that dIII swivelling might assist in the control of proton gating by the redox state of bound NADP⁺/NADPH during enzyme turnover.
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Affiliation(s)
- J Baz Jackson
- School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK.
| | - Josephine H Leung
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92307, USA
| | - Charles D Stout
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92307, USA
| | | | - Robert B Gennis
- Department of Biochemistry, University of Illinois, Urbana, IL 61801, USA
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3
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Jackson JB. A review of the binding-change mechanism for proton-translocating transhydrogenase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1817:1839-46. [PMID: 22538293 DOI: 10.1016/j.bbabio.2012.04.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Revised: 04/04/2012] [Accepted: 04/10/2012] [Indexed: 11/17/2022]
Abstract
Proton-translocating transhydrogenase is found in the inner membranes of animal mitochondria, and in the cytoplasmic membranes of many bacteria. It catalyses hydride transfer from NADH to NADP(+) coupled to inward proton translocation. Evidence is reviewed suggesting the enzyme operates by a "binding-change" mechanism. Experiments with Escherichia coli transhydrogenase indicate the enzyme is driven between "open" and "occluded" states by protonation and deprotonation reactions associated with proton translocation. In the open states NADP(+)/NADPH can rapidly associate with, or dissociate from, the enzyme, and hydride transfer is prevented. In the occluded states bound NADP(+)/NADPH cannot dissociate, and hydride transfer is allowed. Crystal structures of a complex of the nucleotide-binding components of Rhodospirillum rubrum transhydrogenase show how hydride transfer is enabled and disabled at appropriate steps in catalysis, and how release of NADP(+)/NADPH is restricted in the occluded state. Thermodynamic and kinetic studies indicate that the equilibrium constant for hydride transfer on the enzyme is elevated as a consequence of the tight binding of NADPH relative to NADP(+). The protonation site in the translocation pathway must face the outside if NADP(+) is bound, the inside if NADPH is bound. Chemical shift changes detected by NMR may show where alterations in protein conformation resulting from NADP(+) reduction are initiated. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).
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4
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Huxley L, Quirk PG, Cotton NPJ, White SA, Jackson JB. The specificity of proton-translocating transhydrogenase for nicotinamide nucleotides. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2010; 1807:85-94. [PMID: 20732298 DOI: 10.1016/j.bbabio.2010.08.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2010] [Accepted: 08/10/2010] [Indexed: 11/29/2022]
Abstract
In its forward direction, transhydrogenase couples the reduction of NADP(+) by NADH to the outward translocation of protons across the membrane of bacteria and animal mitochondria. The enzyme has three components: dI and dIII protrude from the membrane and dII spans the membrane. Hydride transfer takes place between nucleotides bound to dI and dIII. Studies on the kinetics of a lag phase at the onset of a "cyclic reaction" catalysed by complexes of the dI and dIII components of transhydrogenase from Rhodospirillum rubrum, and on the kinetics of fluorescence changes associated with nucleotide binding, reveal two features. Firstly, the binding of NADP(+) and NADPH to dIII is extremely slow, and is probably limited by the conversion of the occluded to the open state of the complex. Secondly, dIII can also bind NAD(+) and NADH. Extrapolating to the intact enzyme this binding to the "wrong" site could lead to slip: proton translocation without change in the nucleotide redox state, which would have important consequences for bacterial and mitochondrial metabolism.
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Affiliation(s)
- Lucinda Huxley
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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5
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Tveen Jensen K, Strambini G, Gonnelli M, Broos J, Jackson JB. Mutations in transhydrogenase change the fluorescence emission state of TRP72 from 1La to 1Lb. Biophys J 2008; 95:3419-28. [PMID: 18599622 PMCID: PMC2547450 DOI: 10.1529/biophysj.108.134650] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2008] [Accepted: 06/17/2008] [Indexed: 11/18/2022] Open
Abstract
The dI component of Rhodospirillum rubrum transhydrogenase has a single Trp residue (Trp(72)), which has distinctive optical properties, including short-wavelength fluorescence emission with clear vibrational fine structure, and long-lived, well-resolved phosphorescence emission. We have made a set of mutant dI proteins in which residues contacting Trp(72) are conservatively substituted. The room-temperature fluorescence-emission spectra of our three Met(97) mutants are blue shifted by approximately 4 nm, giving them a shorter-wavelength emission than any other protein described in the literature, including azurin from Pseudomonas aeruginosa. Fluorescence spectra in low-temperature glasses show equivalent well-resolved vibrational bands in wild-type and the mutant dI proteins, and in azurin. Substitution of Met(97) in dI changes the relative intensities of some of these vibrational bands. The analysis supports the view that fluorescence from the Met(97) mutants arises predominantly from the (1)L(b) excited singlet state of Trp(72), whereas (1)L(a) is the predominant emitting state in wild-type dI. It is suggested that the sulfur atom of Met(97) promotes greater stabilization of (1)L(a) than either (1)L(b) or the ground state. The phosphorescence spectra of Met(97) mutants are also blue-shifted, indicating that the sulfur atom decreases the transition energy between the (3)L(a) state of the Trp and the ground state.
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Affiliation(s)
- Karina Tveen Jensen
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
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6
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Obiozo UM, Brondijk THC, White AJ, van Boxel G, Dafforn TR, White SA, Jackson JB. Substitution of Tyrosine 146 in the dI Component of Proton-translocating Transhydrogenase Leads to Reversible Dissociation of the Active Dimer into Inactive Monomers. J Biol Chem 2007; 282:36434-43. [PMID: 17911104 DOI: 10.1074/jbc.m705433200] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Transhydrogenase couples the redox reaction between NADH and NADP+ to proton translocation across a membrane. The protein has three components: dI binds NADH, dIII binds NADP+, and dII spans the membrane. Transhydrogenase is a "dimer" of two dI-dII-dIII "monomers"; x-ray structures suggested that the two catalytic sites alternate during turnover. Invariant Tyr146 in recombinant dI of Rhodospirillum rubrum transhydrogenase was substituted with Phe and Ala (proteins designated dI.Y146F and dI.Y146A, respectively). Analytical ultracentrifuge experiments and differential scanning calorimetry show that dI.Y146A more readily dissociates into monomers than wild-type dI. Analytical ultracentrifuge and Trp fluorescence experiments indicate that the dI.Y146A monomers bind NADH much more weakly than dimers. Wild-type dI and dI.Y146F reconstituted activity to dI-depleted membranes with similar characteristics. However, dI.Y146A reconstituted activity in its dimeric form but not in its monomeric form, this despite monomers retaining their native fold and binding to the dI-depleted membranes. It is suggested that transhydrogenase reconstructed with monomers of dI.Y146A is catalytically compromised, at least partly as a consequence of the lowered affinity for NADH, and this results from lost interactions between the nucleotide binding site and the protein beta-hairpin upon dissociation of the dI dimer. The importance of these interactions and their coupling to dI domain rotation in the mechanism of action of transhydrogenase is emphasized. Two peaks in the 1H NMR spectrum of wild-type dI are broadened in dI.Y146A and are tentatively assigned to S-methyl groups of Met resonances in the beta-hairpin, consistent with the segmental mobility of this feature in the structure.
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Affiliation(s)
- U Mirian Obiozo
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
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7
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Broos J, Tveen-Jensen K, de Waal E, Hesp BH, Jackson JB, Canters GW, Callis PR. The emitting state of tryptophan in proteins with highly blue-shifted fluorescence. Angew Chem Int Ed Engl 2007; 46:5137-9. [PMID: 17539030 DOI: 10.1002/anie.200700839] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Jaap Broos
- Department of Biophysical, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
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8
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Broos J, Tveen-Jensen K, de Waal E, Hesp B, Jackson J, Canters G, Callis P. The Emitting State of Tryptophan in Proteins with Highly Blue-Shifted Fluorescence. Angew Chem Int Ed Engl 2007. [DOI: 10.1002/ange.200700839] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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9
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Bhakta T, Whitehead SJ, Snaith JS, Dafforn TR, Wilkie J, Rajesh S, White SA, Jackson JB. Structures of the dI2dIII1 complex of proton-translocating transhydrogenase with bound, inactive analogues of NADH and NADPH reveal active site geometries. Biochemistry 2007; 46:3304-18. [PMID: 17323922 DOI: 10.1021/bi061843r] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Transhydrogenase couples the redox reaction between NADH and NADP+ to proton translocation across a membrane. The enzyme comprises three components; dI binds NAD(H), dIII binds NADP(H), and dII spans the membrane. The 1,4,5,6-tetrahydro analogue of NADH (designated H2NADH) bound to isolated dI from Rhodospirillum rubrum transhydrogenase with similar affinity to the physiological nucleotide. Binding of either NADH or H2NADH led to closure of the dI mobile loop. The 1,4,5,6-tetrahydro analogue of NADPH (H2NADPH) bound very tightly to isolated R. rubrum dIII, but the rate constant for dissociation was greater than that for NADPH. The replacement of NADP+ on dIII either with H2NADPH or with NADPH caused a similar set of chemical shift alterations, signifying an equivalent conformational change. Despite similar binding properties to the natural nucleotides, neither H2NADH nor H2NADPH could serve as a hydride donor in transhydrogenation reactions. Mixtures of dI and dIII form dI2dIII1 complexes. The nucleotide charge distribution of complexes loaded either with H2NADH and NADP+ or with NAD+ and H2NADPH should more closely mimic the ground states for forward and reverse hydride transfer, respectively, than previously studied dead-end species. Crystal structures of such complexes at 2.6 and 2.3 A resolution are described. A transition state for hydride transfer between dihydronicotinamide and nicotinamide derivatives determined in ab initio quantum mechanical calculations resembles the organization of nucleotides in the transhydrogenase active site in the crystal structure. Molecular dynamics simulations of the enzyme indicate that the (dihydro)nicotinamide rings remain close to a ground state for hydride transfer throughout a 1.4 ns trajectory.
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Affiliation(s)
- Tina Bhakta
- School of Biosciences, University of Birmingham, Edgbaston, UK
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10
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Wilson R, Obiozo UM, Quirk PG, Besra GS, Jackson JB. A hybrid of the transhydrogenases from Rhodospirillum rubrum and Mycobacterium tuberculosis catalyses rapid hydride transfer but not the complete, proton-translocating reaction. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:215-23. [PMID: 16624251 DOI: 10.1016/j.bbabio.2006.03.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2006] [Revised: 02/24/2006] [Accepted: 03/05/2006] [Indexed: 11/28/2022]
Abstract
All transhydrogenases appear to have three components: dI, which binds NAD(H), and dIII, which binds NADP(H), protrude from the membrane, and dII spans the membrane. However, the polypeptide composition of the enzymes varies amongst species. The transhydrogenases of Mycobacterium tuberculosis and of Rhodospirillum rubrum have three polypeptides. Sequence analysis indicates that an ancestral three-polypeptide enzyme evolved into transhydrogenases with either two polypeptides (such as the Escherichia coli enzyme) or one polypeptide (such as the mitochondrial enzyme). The fusion steps in each case probably led to the development of an additional transmembrane helix. A hybrid transhydrogenase was constructed from the dI component of the M. tuberculosis enzyme and the dII and dIII components of the R. rubrum enzyme. The hybrid catalyses cyclic transhydrogenation but not the proton-translocating, reverse reaction. This shows that nucleotide-binding/release at the NAD(H) site, and hydride transfer, are fully functional but that events associated with NADP(H) binding/release are compromised. It is concluded that sequence mismatch in the hybrid prevents a conformational change between dI and dIII which is essential for the step accompanying proton translocation.
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Affiliation(s)
- Rosalind Wilson
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
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11
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Brondijk THC, van Boxel GI, Mather OC, Quirk PG, White SA, Jackson JB. The role of invariant amino acid residues at the hydride transfer site of proton-translocating transhydrogenase. J Biol Chem 2006; 281:13345-13354. [PMID: 16533815 DOI: 10.1074/jbc.m513230200] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Transhydrogenase couples proton translocation across a membrane to hydride transfer between NADH and NADP+. Previous x-ray structures of complexes of the nucleotide-binding components of transhydrogenase ("dI2dIII1" complexes) indicate that the dihydronicotinamide ring of NADH can move from a distal position relative to the nicotinamide ring of NADP+ to a proximal position. The movement might be responsible for gating hydride transfer during proton translocation. We have mutated three invariant amino acids, Arg-127, Asp-135, and Ser-138, in the NAD(H)-binding site of Rhodospirillum rubrum transhydrogenase. In each mutant, turnover by the intact enzyme is strongly inhibited. Stopped-flow experiments using dI2dIII1 complexes show that inhibition results from a block in the steps associated with hydride transfer. Mutation of Asp-135 and Ser-138 had no effect on the binding affinity of either NAD+ or NADH, but mutation of Arg-127 led to much weaker binding of NADH and slightly weaker binding of NAD+. X-ray structures of dI2dIII1 complexes carrying the mutations showed that their effects were restricted to the locality of the bound NAD(H). The results are consistent with the suggestion that in wild-type protein movement of the Arg-127 side chain, and its hydrogen bonding to Asp-135 and Ser-138, stabilizes the dihydronicotinamide of NADH in the proximal position for hydride transfer.
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Affiliation(s)
- T Harma C Brondijk
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - Gijs I van Boxel
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - Owen C Mather
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - Philip G Quirk
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - Scott A White
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
| | - J Baz Jackson
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
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12
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Bizouarn T, van Boxel GI, Bhakta T, Jackson JB. Nucleotide binding affinities of the intact proton-translocating transhydrogenase from Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1708:404-10. [PMID: 15935988 DOI: 10.1016/j.bbabio.2005.04.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2005] [Revised: 04/28/2005] [Accepted: 04/29/2005] [Indexed: 12/01/2022]
Abstract
Transhydrogenase (E.C. 1.6.1.1) couples the redox reaction between NAD(H) and NADP(H) to the transport of protons across a membrane. The enzyme is composed of three components. The dI and dIII components, which house the binding site for NAD(H) and NADP(H), respectively, are peripheral to the membrane, and dII spans the membrane. We have estimated dissociation constants (K(d) values) for NADPH (0.87 microM), NADP(+) (16 microM), NADH (50 microM), and NAD(+) (100-500 microM) for intact, detergent-dispersed transhydrogenase from Escherichia coli using micro-calorimetry. This is the first complete set of dissociation constants of the physiological nucleotides for any intact transhydrogenase. The K(d) values for NAD(+) and NADH are similar to those previously reported with isolated dI, but the K(d) values for NADP(+) and NADPH are much larger than those previously reported with isolated dIII. There is negative co-operativity between the binding sites of the intact, detergent-dispersed transhydrogenase when both nucleotides are reduced or both are oxidized.
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Affiliation(s)
- Tania Bizouarn
- Laboratoire de Chimie Physique, Bat 350, Université Paris XI-Orsay, 91405 Orsay, France
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13
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Whitehead SJ, Rossington KE, Hafiz A, Cotton NPJ, Jackson JB. Zinc ions selectively inhibit steps associated with binding and release of NADP(H) during turnover of proton-translocating transhydrogenase. FEBS Lett 2005; 579:2863-7. [PMID: 15878164 DOI: 10.1016/j.febslet.2005.04.026] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2005] [Revised: 04/07/2005] [Accepted: 04/07/2005] [Indexed: 10/25/2022]
Abstract
Transhydrogenase couples the redox reaction between NAD(H) and NADP(H) to proton translocation across a membrane. In membrane vesicles from Escherichia coli and Rhodospirillum rubrum, the transhydrogenase reaction (measured in the direction driving inward proton translocation) was inhibited by Zn(2+) and Cd(2+). However, depending on pH, the metal ions either had no effect on, or stimulated, "cyclic" transhydrogenation. They must, therefore, interfere specifically with steps involving binding/release of NADP(+)/NADPH: the steps thought to be associated with proton translocation. It is suggested that Zn(2+) and Cd(2+) bind in the proton-transfer pathway and block inter-conversion of states responsible for changing NADP(+)/NADPH binding energy.
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14
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Mather OC, Singh A, van Boxel GI, White SA, Jackson JB. Active-site conformational changes associated with hydride transfer in proton-translocating transhydrogenase. Biochemistry 2004; 43:10952-64. [PMID: 15323555 DOI: 10.1021/bi0497594] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Transhydrogenase couples the redox (hydride-transfer) reaction between NAD(H) and NADP(H) to proton translocation across a membrane. The redox reaction is catalyzed at the interface between two components (dI and dIII) which protrude from the membrane. A complex formed from recombinant dI and dIII (the dI(2)dIII(1) complex) from Rhodospirillum rubrum transhydrogenase catalyzes fast single-turnover hydride transfer between bound nucleotides. In this report we describe three new crystal structures of the dI(2)dIII(1) complex in different nucleotide-bound forms. The structures reveal an asymmetry in nucleotide binding that complements results from solution studies and supports the notion that intact transhydrogenase functions by an alternating site mechanism. In one structure, the redox site is occupied by NADH (on dI) and NADPH (on dIII). The dihydronicotinamide rings take up positions which may approximate to the ground state for hydride transfer: the redox-active C4(N) atoms are separated by only 3.6 A, and the perceived reaction stereochemistry matches that observed experimentally. The NADH conformation is different in the two dI polypeptides of this form of the dI(2)dIII(1) complex. Comparisons between a number of X-ray structures show that a conformational change in the NADH is driven by relative movement of the two domains which comprise dI. It is suggested that an equivalent conformational change in the intact enzyme is important in gating the hydride-transfer reaction. The observed nucleotide conformational change in the dI(2)dIII(1) complex is accompanied by rearrangements in the orientation of local amino acid side chains which may be responsible for sealing the site from the solvent and polarizing hydride transfer.
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Affiliation(s)
- Owen C Mather
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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15
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Broos J, Gabellieri E, van Boxel GI, Jackson JB, Strambini GB. Tryptophan phosphorescence spectroscopy reveals that a domain in the NAD(H)-binding component (dI) of transhydrogenase from Rhodospirillum rubrum has an extremely rigid and conformationally homogeneous protein core. J Biol Chem 2003; 278:47578-84. [PMID: 12972415 DOI: 10.1074/jbc.m309287200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The characteristics of tryptophan phosphorescence from the NAD(H)-binding component (dI) component of Rhodospirillum rubrum transhydrogenase are described. This enzyme couples hydride transfer between NAD(H) and NADP(H) to proton translocation across a membrane and is only active as a dimer. Tryptophan phosphorescence spectroscopy is a sensitive technique for the detection of protein conformational changes and was used here to characterize dI under mechanistically relevant conditions. Our results indicate that the single tryptophan in dI, Trp-72, is embedded in a rigid, compact, and homogeneous protein matrix that efficiently suppresses collisional quenching processes and results in the longest triplet lifetime for Trp ever reported in a protein at ambient temperature (2.9 s). The protein matrix surrounding Trp-72 is extraordinarily rigid up to 50 degrees C. In all previous studies on Trp-containing proteins, changes in structure were reflected in a different triplet lifetime. In dI, the lifetime of Trp-72 phosphorescence was barely affected by protein dimerization, cofactor binding, complexation with the NADP(H)-binding component (dIII), or by the introduction of two amino acid substitutions at the hydride-transfer site. It is suggested that the rigidity and structural invariance of the protein domain (dI.1) housing this Trp residue are important to the mechanism of transhydrogenase: movement of dI.1 affects the width of a cleft which, in turn, regulates the positioning of bound nucleotides ready for hydride transfer. The unique protein core in dI may be a paradigm for the design of compact and stable de novo proteins.
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Affiliation(s)
- Jaap Broos
- Department of Biochemistry and Groningen Biomolecular Science and Biotechnology Institute, University of Groningen, 9747 AG Groningen, The Netherlands
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16
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Singh A, Venning JD, Quirk PG, van Boxel GI, Rodrigues DJ, White SA, Jackson JB. Interactions between transhydrogenase and thio-nicotinamide Analogues of NAD(H) and NADP(H) underline the importance of nucleotide conformational changes in coupling to proton translocation. J Biol Chem 2003; 278:33208-16. [PMID: 12791694 DOI: 10.1074/jbc.m303061200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Transhydrogenase couples the reduction of NADP+ by NADH to inward proton translocation across mitochondrial and bacterial membranes. The coupling reactions occur within the protein by long distance conformational changes. In intact transhydrogenase and in complexes formed from the isolated, nucleotide-binding components, thio-NADP(H) is a good analogue for NADP(H), but thio-NAD(H) is a poor analogue for NAD(H). Crystal structures of the nucleotide-binding components show that the twists of the 3-carbothiamide groups of thio-NADP+ and of thio-NAD+ (relative to the planes of the pyridine rings), which are defined by the dihedral, Xam, are altered relative to the twists of the 3-carboxamide groups of the physiological nucleotides. The finding that thio-NADP+ is a good substrate despite an increased Xam value shows that approach of the NADH prior to hydride transfer is not obstructed by the S atom in the analogue. That thio-NAD(H) is a poor substrate appears to be the result of failure in the conformational change that establishes the ground state for hydride transfer. This might be a consequence of restricted rotation of the 3-carbothiamide group during the conformational change.
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Affiliation(s)
- Avtar Singh
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
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17
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Abstract
Transhydrogenase, in animal mitochondria and bacteria, couples hydride transfer between NADH and NADP(+) to proton translocation across a membrane. Within the protein, the redox reaction occurs at some distance from the proton translocation pathway and coupling is achieved through conformational changes. In an 'open' conformation of transhydrogenase, in which substrate nucleotides bind and product nucleotides dissociate, the dihydronicotinamide and nicotinamide rings are held apart to block hydride transfer; in an 'occluded' conformation, they are moved into apposition to permit the redox chemistry. In the two monomers of transhydrogenase, there is a reciprocating, out-of-phase alternation of these conformations during turnover.
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Affiliation(s)
- J Baz Jackson
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
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18
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van Boxel GI, Quirk PG, Cotton NPJ, White SA, Jackson JB. Glutamine 132 in the NAD(H)-binding component of proton-translocating transhydrogenase tethers the nucleotides before hydride transfer. Biochemistry 2003; 42:1217-26. [PMID: 12564924 DOI: 10.1021/bi027032e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Transhydrogenase, found in bacterial membranes and inner mitochondrial membranes of animal cells, couples the redox reaction between NAD(H) and NADP(H) to proton translocation. In this work, the invariant Gln132 in the NAD(H)-binding component (dI) of the Rhodospirillum rubrum transhydrogenase was substituted with Asn (to give dI.Q132N). Mixtures of the mutant protein and the NADP(H)-binding component (dIII) of the enzyme readily produced an asymmetric complex, (dI.Q132N)(2)dIII(1). The X-ray structure of the complex revealed specific changes in the interaction between bound nicotinamide nucleotides and the protein at the hydride transfer site. The first-order rate constant of the redox reaction between nucleotides bound to (dI.Q132N)(2)dIII(1) was <1% of that for the wild-type complex, and the deuterium isotope effect was significantly decreased. The nucleotide binding properties of the dI component in the complex were asymmetrically affected by the Gln-to-Asn mutation. In intact, membrane-bound transhydrogenase, the substitution completely abolished all catalytic activity. The results suggest that Gln132 in the wild-type enzyme behaves as a "tether" or a "tie" in the mutual positioning of the (dihydro)nicotinamide rings of NAD(H) and NADP(H) for hydride transfer during the conformational changes that are coupled to the translocation of protons across the membrane. This ensures that hydride transfer is properly gated and does not take place in the absence of proton translocation.
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Affiliation(s)
- Gijs I van Boxel
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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19
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Rodrigues DJ, Jackson JB. A conformational change in the isolated NADP(H)-binding component (dIII) of transhydrogenase induced by low pH: a reflection of events during proton translocation by the complete enzyme? BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1555:8-13. [PMID: 12206884 DOI: 10.1016/s0005-2728(02)00247-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Transhydrogenase couples the reduction of NADP(+) by NADH to inward proton translocation across the bacterial (or mitochondrial) membrane. Conformational changes in the NADP(H)-binding component of the enzyme (dIII) are central to the coupling mechanism. In the "open" state, NADP(H) bound to dIII can readily exchange with nucleotides in the solvent but hydride transfer [to/from NAD(H) bound to dI] is prevented. In the "occluded" state, bound NADP(H) cannot exchange with solvent nucleotides but the hydride transfer reaction is permitted. It was previously found that the conformational state of isolated, recombinant dIII is pH dependent. At neutral pH, the protein adopts a conformation resembling the occluded state, and at low pH, it adopts a conformation resembling the open state. The crystal structure of dIII indicates that the loop E "lid" might be largely responsible for the very high affinity of the protein for NADP(H). In this paper we show, using fluorescence resonance energy transfer, that the distance between the apex of loop E of isolated dIII, and the core of the protein, increases when the solution pH is lowered. This is consistent with the view that the lid is retracted to permit NADPH release during turnover of the complete enzyme.
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20
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Weston CJ, Venning JD, Jackson JB. The membrane-peripheral subunits of transhydrogenase from Entamoeba histolytica are functional only when dimerized. J Biol Chem 2002; 277:26163-70. [PMID: 12004068 DOI: 10.1074/jbc.m203514200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Unlike their bacterial and mammalian counterparts, the NADP(H)- and NAD(H)-binding components of proton-translocating transhydrogenase from the protozoan parasite Entamoeba histolytica (denoted ehdIII and ehdI, respectively) are tethered by a polypeptide linker. The recombinant tethered fragment, ehdIII-ehdI, was prepared without its membrane-spanning dII component. Dimers of ehdIII-ehdI catalyzed transhydrogenation, but monomers were inactive. The addition of ehdIII to ehdIII-ehdI monomers did not lead to an increase in the rate of transhydrogenation, showing that this inactivity is not the result of an unfavorable topology introduced by the linker. The addition of a bacterial dI to ehdIII-ehdI led to an increase in the rate of transhydrogenation, showing that the linker is flexible. A hybrid protein in which ehdIII is tethered to the bacterial dI (denoted ehdIII-rrdI) more readily formed active dimers. Data from small angle x-ray scattering by the hybrid dimers were fitted to models derived from the high-resolution crystal structure of the bacterial dI(2)dIII(1) complex (Cotton, N. P. J., White, S. A., Peake, S. J., McSweeney, S., and Jackson, J. B. (2001) Structure 9, 165-T176). The results show that the ehdIII-rrdI dimer is asymmetric; one dIII associates with dI, as in the bacterial complex, but the other is displaced. The results provide evidence for the alternating site, binding change model for proton translocation by intact transhydrogenase.
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Affiliation(s)
- Chris J Weston
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
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21
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Jackson JB, White SA, Quirk PG, Venning JD. The alternating site, binding change mechanism for proton translocation by transhydrogenase. Biochemistry 2002; 41:4173-85. [PMID: 11914062 DOI: 10.1021/bi012078d] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- J Baz Jackson
- School of Biochemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
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22
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Venning JD, Rodrigues DJ, Weston CJ, Cotton NP, Quirk PG, Errington N, Finet S, White SA, Jackson JB. The heterotrimer of the membrane-peripheral components of transhydrogenase and the alternating-site mechanism of proton translocation. J Biol Chem 2001; 276:30678-85. [PMID: 11399770 DOI: 10.1074/jbc.m104429200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Transhydrogenase undergoes conformational changes to couple the redox reaction between NAD(H) and NADP(H) to proton translocation across a membrane. The protein comprises three components: dI, which binds NAD(H); dIII, which binds NADP(H); and dII, which spans the membrane. Experiments using isothermal titration calorimetry, analytical ultracentrifugation, and small angle x-ray scattering show that, as in the crystalline state, a mixture of recombinant dI and dIII from Rhodospirillum rubrum transhydrogenase readily forms a dI(2)dIII(1) heterotrimer in solution, but we could find no evidence for the formation of a dI(2)dIII(2) tetramer using these techniques. The asymmetry of the complex suggests that there is an alternation of conformations at the nucleotide-binding sites during proton translocation by the complete enzyme. The characteristics of nucleotide interaction with the isolated dI and dIII components and with the dI(2)dIII(1) heterotrimer were investigated. (a) The rate of release of NADP(+) from dIII was decreased 5-fold when the component was incorporated into the heterotrimer. (b) The binding affinity of one of the two nucleotide-binding sites for NADH on the dI dimer was decreased about 17-fold in the dI(2)dIII(1) complex; the other binding site was unaffected. These observations lend strong support to the alternating-site mechanism.
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Affiliation(s)
- J D Venning
- School of Biosciences, University of Birmingham, Edgbaston, United Kingdom
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23
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Studley WK, Yamaguchi M, Hatefi Y, Saier MH. Phylogenetic analyses of proton-translocating transhydrogenases. MICROBIAL & COMPARATIVE GENOMICS 2001; 4:173-86. [PMID: 10587945 DOI: 10.1089/omi.1.1999.4.173] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The proton-translocating nicotinamide nucleotide transhydrogenases (TH) provide a simple model for understanding chemically coupled transmembrane proton translocation. To further our understanding of TH structure-function relationships, we have identified all sequenced homologous of these vectorial enzymes and have conducted sequence comparison studies. The NAD-binding domains of TH are homologous to bacterial alanine dehydrogenases (ADH) and eukaryotic saccharopine dehydrogenases (SDH) as well as N5(carboxyethyl)-L-ornithine synthase of Lactococcus lactis and dipicolinate synthase of Bacillus subtilis. A multiple alignment, a phylogenetic tree, and two signature sequences for this family, designated the TH-ADH-SDH or TAS superfamily, have been derived. Additionally, the TH family has been characterized. Phylogenetic analyses suggested that these proteins have evolved without inter-system shuffling. However, interdomain splicing-fusion events have occurred during the evolution of several of these systems. Analyses of the multiple alignment for the TH family revealed that domain conservation occurs in the order: NADP-binding domain (domain III) > NAD-binding domain (domain I) > proton-translocating transmembrane domain (domain II). A topologic model for the proton-translocating transmembrane domain consistent with published data is presented, and a possible involvement of specific transmembrane alpha-helical segments in channel formation is suggested.
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Affiliation(s)
- W K Studley
- Department of Biology, University of California at San Diego, La Jolla, USA
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24
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Rodrigues DJ, Venning JD, Quirk PG, Jackson JB. A change in ionization of the NADP(H)-binding component (dIII) of proton-translocating transhydrogenase regulates both hydride transfer and nucleotide release. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:1430-8. [PMID: 11231296 DOI: 10.1046/j.1432-1327.2001.02008.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Transhydrogenase couples the transfer of hydride-ion equivalents between NAD(H) and NADP(H) to proton translocation across a membrane. The enzyme has three components: dI binds NAD(H), dIII binds NADP(H) and dII spans the membrane. Coupling between transhydrogenation and proton translocation involves changes in the binding of NADP(H). Mixtures of isolated dI and dIII from Rhodospirillum rubrum transhydrogenase catalyse a rapid, single-turnover burst of hydride transfer between bound nucleotides; subsequent turnover is limited by NADP(H) release. Stopped-flow experiments showed that the rate of the hydride transfer step is decreased at low pH. Single Trp residues were introduced into dIII by site-directed mutagenesis. Two mutants with similar catalytic properties to those of the wild-type protein were selected for a study of nucleotide release. The way in which Trp fluorescence was affected by nucleotide occupancy of dIII was different in the two mutants, and hence two different procedures for determining the rate of nucleotide release were developed. The apparent first-order rate constants for NADP(+) release and NADPH release from isolated dIII increased dramatically at low pH. It is concluded that a single ionisable group in dIII controls both the rate of hydride transfer and the rate of nucleotide release. The properties of the protonated and unprotonated forms of dIII are consistent with those expected of intermediates in the NADP(H)-binding-change mechanism. The ionisable group might be a component of the proton-translocation pathway in the complete enzyme.
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Affiliation(s)
- D J Rodrigues
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham, UK
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25
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Cotton NP, White SA, Peake SJ, McSweeney S, Jackson JB. The crystal structure of an asymmetric complex of the two nucleotide binding components of proton-translocating transhydrogenase. Structure 2001; 9:165-76. [PMID: 11250201 DOI: 10.1016/s0969-2126(01)00571-8] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND Membrane-bound ion translocators have important functions in biology, but their mechanisms of action are often poorly understood. Transhydrogenase, found in animal mitochondria and bacteria, links the redox reaction between NAD(H) and NADP(H) to proton translocation across a membrane. Linkage is achieved through changes in protein conformation at the nucleotide binding sites. The redox reaction takes place between two protein components located on the membrane surface: dI, which binds NAD(H), and dIII, which binds NADP(H). A third component, dII, provides a proton channel through the membrane. Intact membrane-located transhydrogenase is probably a dimer (two copies each of dI, dII, and dIII). RESULTS We have solved the high-resolution crystal structure of a dI:dIII complex of transhydrogenase from Rhodospirillum rubrum-the first from a transhydrogenase of any species. It is a heterotrimer, having two polypeptides of dI and one of dIII. The dI polypeptides fold into a dimer. The loop on dIII, which binds the nicotinamide ring of NADP(H), is inserted into the NAD(H) binding cleft of one of the dI polypeptides. The cleft of the other dI is not occupied by a corresponding dIII component. CONCLUSIONS The redox step in the transhydrogenase reaction is readily visualized; the NC4 atoms of the nicotinamide rings of the bound nucleotides are brought together to facilitate direct hydride transfer with A-B stereochemistry. The asymmetry of the dI:dIII complex suggests that in the intact enzyme there is an alternation of conformation at the catalytic sites associated with changes in nucleotide binding during proton translocation.
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Affiliation(s)
- N P Cotton
- School of Biosciences, University of Birmingham, Edgbaston, B15 2TT, Birmingham, United Kingdom
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26
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Bergkvist A, Johansson C, Johansson T, Rydström J, Karlsson BG. Interactions of the NADP(H)-binding domain III of proton-translocating transhydrogenase from escherichia coli with NADP(H) and the NAD(H)-binding domain I studied by NMR and site-directed mutagenesis. Biochemistry 2000; 39:12595-605. [PMID: 11027139 DOI: 10.1021/bi0004091] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Using the purified NADP(H)-binding domain of proton-translocating Escherichia coli transhydrogenase (ecIII) overexpressed in (15)N- and (2)H-labeled medium, together with the purified NAD(H)-binding domain from E. coli (ecI), the interface between ecIII and ecI, the NADP(H)-binding site and the influence on the interface by NAD(P)(H) was investigated in solution by NMR chemical shift mapping. Mapping of the NADP(H)-binding site showed that the NADP(H) substrate is bound to ecIII in an extended conformation at the C-terminal end of the parallel beta-sheet. The distribution of chemical shift perturbations in the NADP(H)-binding site, and the nature of the interaction between ecI and ecIII, indicated that the nicotinamide moiety of NADP(H) is located near the loop comprising residues P346-G353, in agreement with the recently determined crystal structures of bovine [Prasad, G. S., et al. (1999) Nat. Struct. Biol. 6, 1126-1131] and human heart [White, A. W., et al. (2000) Structure 8, 1-12] transhydrogenases. Further chemical shift perturbation analysis also identified regions comprising residues G389-I406 and G430-V434 at the C-terminal end of ecIII's beta-sheet as part of the ecI-ecIII interface, which were regulated by the redox state of the NAD(P)(H) substrates. To investigate the role of these loop regions in the interaction with domain I, the single cysteine mutants T393C, R425C, G430C, and A432C were generated in ecIII and the transhydrogenase activities of the resulting mutant proteins characterized using the NAD(H)-binding domain I from Rhodospirillum rubrum (rrI). All mutants except R425C showed altered NADP(H) binding and domain interaction properties. In contrast, the R425C mutant showed almost exclusively changes in the NADP(H)-binding properties, without changing the affinity for rrI. Finally, by combining the above conclusions with information obtained by a further characterization of previously constructed mutants, the implications of the findings were considered in a mechanistic context.
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Affiliation(s)
- A Bergkvist
- Department of Biochemistry and Biophysics, Göteborg University, S-413 90 Göteborg, Sweden.
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27
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Jeeves M, Smith KJ, Quirk PG, Cotton NP, Jackson JB. Solution structure of the NADP(H)-binding component (dIII) of proton-translocating transhydrogenase from Rhodospirillum rubrum. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1459:248-57. [PMID: 11004437 DOI: 10.1016/s0005-2728(00)00159-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Transhydrogenase is a proton pump found in the membranes of bacteria and animal mitochondria. The solution structure of the expressed, 21.5 kDa, NADP(H)-binding component (dIII) of transhydrogenase from Rhodospirillum rubrum has been solved by NMR methods. This is the first description of the structure of dIII from a bacterial source. The protein adopts a Rossmann fold: an open, twisted, parallel beta-sheet, flanked by helices. However, the binding of NADP(+) to dIII is profoundly different to that seen in other Rossmann structures, in that its orientation is reversed: the adenosine moiety interacts with the first betaalphabetaalphabeta motif, and the nicotinamide with the second. Features in the structure that might be responsible for changes in nucleotide-binding affinity during catalysis, and for interaction with other components of the enzyme, are identified. The results are compared with the recently determined, high-resolution crystal structures of human and bovine dIII which also show the reversed nucleotide orientation.
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Affiliation(s)
- M Jeeves
- School of Biosciences, University of Birmingham, Edgbaston, B15 2TT, UK
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28
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Bizouarn T, Meuller J, Axelsson M, Rydström J. The transmembrane domain and the proton channel in proton-pumping transhydrogenases. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1459:284-90. [PMID: 11004441 DOI: 10.1016/s0005-2728(00)00163-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Proton-pumping nicotinamide nucleotide transhydrogenases are composed of three main domains, the NAD(H)-binding and NADP(H)-binding hydrophilic domains I (dI) and III (dIII), respectively, and the hydrophobic domain II (dII) containing the assumed proton channel. dII in the Escherichia coli enzyme has recently been characterised with regard to topology and a packing model of the helix bundle in dII is proposed. Extensive mutagenesis of conserved charged residues of this domain showed that important residues are betaHis91 and betaAsn222. The pH dependence of betaH91D, as well as betaH91C (unpublished), when compared to that of wild type shows that reduction of 3-acetylpyridine-NAD(+) by NADPH, i.e., the reverse reaction, is optimal at a pH essentially coinciding with the pK(a) of the residue in the beta91 position. It is therefore concluded that the wild-type transhydrogenase is regulated by the degree of protonation of betaHis91. The mechanisms of the interactions between dI+dIII and dII are suggested to involve pronounced conformational changes in a 'hinge' region around betaR265.
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Affiliation(s)
- T Bizouarn
- Department of Biochemistry and Biophysics, Göteborg University, Sweden
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29
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Buckley PA, Baz Jackson J, Schneider T, White SA, Rice DW, Baker PJ. Protein-protein recognition, hydride transfer and proton pumping in the transhydrogenase complex. Structure 2000; 8:809-15. [PMID: 10997900 DOI: 10.1016/s0969-2126(00)00171-4] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND Membrane-bound ion pumps are involved in metabolic regulation, osmoregulation, cell signalling, nerve transmission and energy transduction. How the ion electrochemical gradient interacts with the scalar chemistry and how the catalytic machinery is gated to ensure high coupling efficiency are fundamental to the mechanism of action of such pumps. Transhydrogenase is a conformationally coupled proton pump linking a proton gradient to the redox reaction between NAD(H) and NADP(H). The enzyme has three components; dI binds NAD(H), dII spans the membrane and dIII binds NADP(H). RESULTS The first crystal structure of a transhydrogenase dI component (from Rhodospirillum rubrum) has been determined at 2.0 A resolution. The monomer comprises two domains. Both are involved in dimer formation, and one has a Rossmann fold that binds NAD+ in a novel mode. The two domains can adopt different conformations. In the most closed conformation, the nicotinamide ring is expelled from the cleft between the two domains and is exposed on the outside of the protein. In this conformation it is possible to dock the structure of dI/NAD+ with that of a dIII/NADP+ complex to provide the first insights into the molecular basis of the hydride-transfer step. CONCLUSIONS Analysis of the model of the dI/dIII complex identifies residues potentially involved in dI/dIII interaction and shows how domain motion in dI results in a shift in position of the nicotinamide ring of NAD+. We propose that this movement is responsible for switching between the forbidden and allowed states for hydride transfer during proton pumping.
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Affiliation(s)
- P A Buckley
- Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, UK
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30
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Venning JD, Peake SJ, Quirk PG, Jackson JB. Stopped-flow reaction kinetics of recombinant components of proton-translocating transhydrogenase with physiological nucleotides. J Biol Chem 2000; 275:19490-7. [PMID: 10747934 DOI: 10.1074/jbc.m000577200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
New information on the high resolution structure of the membrane proton pump, transhydrogenase, now provides a framework for understanding kinetic descriptions of the enzyme. Here, we have studied redox reactions catalyzed by mixtures of the recombinant NAD(H)-binding component (dI) of Rhodospirillum rubrum transhydrogenase, and the recombinant NADP(H)-binding component (dIII) of either the R. rubrum enzyme or the human enzyme. By recording changes in the fluorescence emission of native and engineered Trp residues, the rates of the redox reaction with physiological nucleotides have been measured under stopped-flow conditions, for the first time. Rate constants for the binding reaction between NAD(+)/NADH and the R. rubrum dI.dIII complex are much greater than those between nucleotide and isolated dI. For the redox step between the physiological nucleotides on the R. rubrum dI. dIII complex, the rate constant in the forward direction, k(f) approximately 2900 s(-1), and that for the reverse reaction, k(r) approximately 110 s(-1). Comparisons with reactions involving an analogue of NAD(H) indicate that the rate constants at this step are strongly affected by the redox driving force.
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Affiliation(s)
- J D Venning
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
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31
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Bizouarn T, Fjellström O, Axelsson M, Korneenko TV, Pestov NB, Ivanova MV, Egorov MV, Shakhparonov M, Rydström J. Interactions between the soluble domain I of nicotinamide nucleotide transhydrogenase from Rhodospirillum rubrum and transhydrogenase from Escherichia coli. Effects on catalytic and H+-pumping activities. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:3281-8. [PMID: 10824114 DOI: 10.1046/j.1432-1327.2000.01358.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Nicotinamide nucleotide transhydrogenase from Escherichia coli is composed of two subunits, the alpha and the beta subunits, each of which contains a hydrophilic domain, domain I and III, respectively, as well as several transmembrane helices, collectively denoted domain II. The interactions between domain I from Rhodospirillum rubrum (rrI) and the intact or the protease-treated enzyme from E. coli was investigated using the separately expressed and purified domain I from R. rubrum, and His-tagged intact and trypsin-treated E. coli transhydrogenase. Despite harsh treatments with, e.g. detergents and denaturing agents, the alpha and beta subunits remained tightly associated. A monoclonal antibody directed towards the alpha subunit was strongly inhibitory, an effect that was relieved by added rrI. In addition, rrI also reactivated the trypsin-digested E. coli enzyme in which domain I had been partly removed. This suggests that the hydrophilic domains I and III are not in permanent contact but are mobile during catalysis while being anchored to domain II. Replacement of domain I of intact, as well as trypsin-digested, E. coli transhydrogenase with rrI resulted in a markedly different pH dependence of the cyclic reduction of 3-acetyl-pyridine-NAD+ by NADH in the presence of NADP(H), suggesting that the protonation of one or more protonable groups in domain I is controlling this reaction. The reverse reaction and proton pumping showed a less pronounced change in pH dependence, demonstrating the regulatory role of domain II in these reactions.
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Affiliation(s)
- T Bizouarn
- Department of Biochemistry and Biophysics, Göteborg University, Sweden
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32
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Bizouarn T, Fjellström O, Meuller J, Axelsson M, Bergkvist A, Johansson C, Göran Karlsson B, Rydström J. Proton translocating nicotinamide nucleotide transhydrogenase from E. coli. Mechanism of action deduced from its structural and catalytic properties. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1457:211-28. [PMID: 10773166 DOI: 10.1016/s0005-2728(00)00103-1] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Transhydrogenase couples the stereospecific and reversible transfer of hydride equivalents from NADH to NADP(+) to the translocation of proton across the inner membrane in mitochondria and the cytoplasmic membrane in bacteria. Like all transhydrogenases, the Escherichia coli enzyme is composed of three domains. Domains I and III protrude from the membrane and contain the binding site for NAD(H) and NADP(H), respectively. Domain II spans the membrane and constitutes at least partly the proton translocating pathway. Three-dimensional models of the hydrophilic domains I and III deduced from crystallographic and NMR data and a new topology of domain II are presented. The new information obtained from the structures and the numerous mutation studies strengthen the proposition of a binding change mechanism, as a way to couple the reduction of NADP(+) by NADH to proton translocation and occurring mainly at the level of the NADP(H) binding site.
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Affiliation(s)
- T Bizouarn
- Department of Biochemistry and Biophysics, Göteborg University, Göteborg, Sweden
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33
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Abstract
Recent developments have led to advances in our understanding of the structure and mechanism of action of proton-translocating (or AB) transhydrogenase. There is (a) a high-resolution crystal structure, and an NMR structure, of the NADP(H)-binding component (dIII), (b) a homology-based model of the NAD(H)-binding component (dI) and (c) an emerging consensus on the position of the transmembrane helices (in dII). The crystal structure of dIII, in particular, provides new insights into the mechanism by which the energy released in proton translocation across the membrane is coupled to changes in the binding affinities of NADP(+) and NADPH that drive the chemical reaction.
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Affiliation(s)
- J B Jackson
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham, UK.
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34
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Peake SJ, Venning JD, Cotton NP, Jackson JB. Evidence for the stabilization of NADPH relative to NADP(+) on the dIII components of proton-translocating transhydrogenases from Homo sapiens and from Rhodospirillum rubrum by measurement of tryptophan fluorescence. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1413:81-91. [PMID: 10514549 DOI: 10.1016/s0005-2728(99)00084-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A unique Trp residue in the recombinant dIII component of transhydrogenase from human heart mitochondria (hsdIII), and an equivalent Trp engineered into the dIII component of Rhodospirillum rubrum transhydrogenase (rrdIII.D155W), are more fluorescent when NADP(+) is bound to the proteins, than when NADPH is bound. We have used this to determine the occupancy of the binding site during transhydrogenation reactions catalysed by mixtures of recombinant dI from the R. rubrum enzyme and either hsdIII or rrdIII.D155W. The standard redox potential of NADP(+)/NADPH bound to the dIII proteins is some 60-70 mV higher than that in free solution. This results in favoured reduction of NADP(+) by NADH at the catalytic site, and supports the view that changes in affinity at the nucleotide-binding site of dIII are central to the mechanism by which transhydrogenase is coupled to proton translocation across the membrane.
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Affiliation(s)
- S J Peake
- School of Biochemistry, University of Birmingham, Edgbaston, Birmingham, UK
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35
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Quirk PG, Smith KJ, Thomas CM, Jackson JB. The mobile loop region of the NAD(H) binding component (dI) of proton-translocating nicotinamide nucleotide transhydrogenase from Rhodospirillum rubrum: complete NMR assignment and effects of bound nucleotides. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1412:139-48. [PMID: 10393257 DOI: 10.1016/s0005-2728(99)00057-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The dI component of transhydrogenase binds NAD+ and NADH. A mobile loop region of dI plays an important role in the nucleotide binding process, and mutations in this region result in impaired hydride transfer in the complete enzyme. We have previously employed one-dimensional 1H-NMR spectroscopy to study wild-type and mutant dI proteins of Rhodospirillum rubrum and the effects of nucleotide binding. Here, we utilise two- and three-dimensional NMR experiments to assign the signals from virtually all of the backbone and side-chain protons of the loop residues. The mobile loop region encompasses 17 residues: Asp223-Met239. The assignments also provide a much strengthened basis for interpreting the structural changes occurring upon nucleotide binding, when the loop closes down onto the surface of the protein and loses mobility. The role of the mobile loop region in catalysis is discussed with particular reference to a newly-developed model of the dI protein, based on its homology with alanine dehydrogenase.
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Affiliation(s)
- P G Quirk
- School of Biochemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
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36
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Peake SJ, Venning JD, Jackson JB. A catalytically active complex formed from the recombinant dI protein of Rhodospirillum rubrum transhydrogenase, and the recombinant dIII protein of the human enzyme. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1411:159-69. [PMID: 10216162 DOI: 10.1016/s0005-2728(99)00013-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Transhydrogenase is a proton pump. It has three components: dI and dIII protrude from the membrane and contain the binding sites for NAD(H) and NADP(H), respectively, and dII spans the membrane. We have expressed dIII from Homo sapiens transhydrogenase (hsdIII) in Escherichia coli. The purified protein was associated with stoichiometric amounts of NADP(H) bound to the catalytic site. The NADP+ and NADPH were released only slowly from the protein, supporting the suggestion that nucleotide-binding by dIII is regulated by the membrane-spanning dII. HsdIII formed a catalytically active complex with recombinant dI from Rhodospirillum rubrum (rrdI), even in the absence of dII. The rates of forward and reverse transhydrogenation catalysed by this complex are probably limited by slow release from dIII of NADPH and NADP+, respectively. The hybrid complex also catalysed high rates of 'cyclic' transhydrogenation, indicating that hydride transfer, and exchange of nucleotides with dI, are rapid. Stopped-flow experiments revealed a rapid, monoexponential, single-turnover burst of reverse transhydrogenation in pre-steady-state. The apparent first-order rate constant of the burst increased with the concentration of rrdI. A deuterium isotope effect (kH/kD approximately 2 at 27 degrees C) was observed when [4B-1H]NADPH was replaced with [4B-2H]NADPH. The characteristics of the burst of transhydrogenation with rrdI:hsdIII differed from those previously reported for rrdI:rrdIII (J.D. Venning et al., Eur. J. Biochem. 257 (1998) 202-209), but the differences are readily explained by a greater dissociation constant of the hybrid complex. The steady-state rate of reverse transhydrogenation by the rrdI:hsdIII complex was almost independent of pH, but there was a single apparent pKa ( approximately 9.1) associated with the cyclic reaction. The reactions of the dI:dIII complex probably proceed independently of those protonation/deprotonation reactions which, in the complete enzyme, are associated with H+ translocation.
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Affiliation(s)
- S J Peake
- School of Biochemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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37
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Quirk PG, Jeeves M, Cotton NP, Smith JK, Jackson BJ. Structural changes in the recombinant, NADP(H)-binding component of proton translocating transhydrogenase revealed by NMR spectroscopy. FEBS Lett 1999; 446:127-32. [PMID: 10100628 DOI: 10.1016/s0014-5793(99)00198-2] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We have analysed 1H, 15N-HSQC spectra of the recombinant, NADP(H)-binding component of transhydrogenase in the context of the emerging three dimensional structure of the protein. Chemical shift perturbations of amino acid residues following replacement of NADP+ with NADPH were observed in both the adenosine and nicotinamide parts of the dinucleotide binding site and in a region which straddles the protein. These observations reflect the structural changes resulting from hydride transfer. The interactions between the recombinant, NADP(H)-binding component and its partner, NAD(H)-binding protein, are complicated. Helix B of the recombinant, NADP(H)-binding component may play an important role in the binding process.
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Affiliation(s)
- P G Quirk
- School of Biochemistry, University of Birmingham, Edgbaston, UK
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38
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Fjellström O, Axelsson M, Bizouarn T, Hu X, Johansson C, Meuller J, Rydström J. Mapping of residues in the NADP(H)-binding site of proton-translocating nicotinamide nucleotide transhydrogenase from Escherichia coli. A study of structure and function. J Biol Chem 1999; 274:6350-9. [PMID: 10037725 DOI: 10.1074/jbc.274.10.6350] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Conformational changes in proton pumping transhydrogenases have been suggested to be dependent on binding of NADP(H) and the redox state of this substrate. Based on a detailed amino acid sequence analysis, it is argued that a classical betaalphabetaalphabeta dinucleotide binding fold is responsible for binding NADP(H). A model defining betaA, alphaB, betaB, betaD, and betaE of this domain is presented. To test this model, four single cysteine mutants (cfbetaA348C, cfbetaA390C, cfbetaK424C, and cfbetaR425C) were introduced into a functional cysteine-free transhydrogenase. Also, five cysteine mutants were constructed in the isolated domain III of Escherichia coli transhydrogenase (ecIIIH345C, ecIIIA348C, ecIIIR350C, ecIIID392C, and ecIIIK424C). In addition to kinetic characterizations, effects of sulfhydryl-specific labeling with N-ethylmaleimide, 2-(4'-maleimidylanilino)naphthalene-6-sulfonic acid, and diazotized 3-aminopyridine adenine dinucleotide (phosphate) were examined. The results are consistent with the view that, in agreement with the model, beta-Ala348, beta-Arg350, beta-Ala390, beta-Asp392, and beta-Lys424 are located in or close to the NADP(H) site. More specifically, beta-Ala348 succeeds betaB. The remarkable reactivity of betaR350C toward NNADP suggests that this residue is close to the nicotinamide moiety of NADP(H). beta-Ala390 and beta-Asp392 terminate or succeed betaD, and are thus, together with the region following betaA, creating the switch point crevice where NADP(H) binds. beta-Asp392 is particularly important for the substrate affinity, but it could also have a more complex role in the coupling mechanism for transhydrogenase.
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Affiliation(s)
- O Fjellström
- Department of Biochemistry and Biophysics, Göteborg University and Chalmers University of Technology, S-405 30, Göteborg, Sweden
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39
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Hu X, Zhang J, Fjellström O, Bizouarn T, Rydström J. Site-directed mutagenesis of charged and potentially proton-carrying residues in the beta subunit of the proton-translocating nicotinamide nucleotide transhydrogenase from Escherichia coli. Characterization of the beta H91, beta D392, and beta K424 mutants. Biochemistry 1999; 38:1652-8. [PMID: 9931033 DOI: 10.1021/bi981654b] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Conserved and semiconserved acidic and basic residues of the beta subunit of the proton-pumping nicotinamide nucleotide transhydrogenase from Escherichia coli potentially involved in proton pumping were investigated. Out of 16 charged residues studied, 6 have not been previously investigated. The most dramatic effects of mutation were observed with beta H91, beta D392, and beta K424. beta H91E showed a pronounced shift of the pH optimum for both reduction of thio-NADP+ by NADH (forward reaction) and reduction of 3-acetylpyridine-NAD+ by NADPH (reverse reaction) to lower pH. This mutant catalyzed a cyclic reduction of 3-acetylpyridine-NAD+ by NADH in the presence of NADP(H) with a pH profile also shifted toward a lower pH. These results are consistent with a mechanism where the normal forward and reverse reactions are indeed limited by protonation/deprotonation of beta H91. The cyclic reaction was affected by mutations of beta H91, probably through conformational changes involving the active NADP(H) site. The beta D392A mutant was inactive with regard to forward and reverse reactions, but showed a wild-type-like pH dependence for the partly active cyclic reaction. However, Km,app for NADP(H) in this reaction was elevated 50-100-fold, suggesting that beta D392 is located in or near the NADP(H)-binding site. Transhydrogenases contain a conserved beta K424-beta R425-beta S426 sequence that has been proposed to be important for NADP(H) binding. beta K424R was strongly inhibited and showed an 18-fold increased Km,app for NADPH in the reverse reaction as compared to wild type. Consequently, this mutation affected all NADP(H)-linked activities and essentially abolished the unspecific interaction of NAD(H) with this site. The pH dependences of the forward and reverse reactions, as well as the cyclic reaction, were shifted to a lower pH as compared to the wild-type enzyme, and the salt dependence was also altered.
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Affiliation(s)
- X Hu
- Department of Biochemistry and Biophysics, Göteborg University, Chalmers University of Technology, Sweden
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40
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Fjellström O, Bizouarn T, Zhang JW, Rydström J, Venning JD, Jackson JB. Catalytic properties of hybrid complexes of the NAD(H)-binding and NADP(H)-binding domains of the proton-translocating transhydrogenases from Escherichia coli and Rhodospirillum rubrum. Biochemistry 1999; 38:415-22. [PMID: 9890924 DOI: 10.1021/bi9817111] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Transhydrogenase couples reversible hydride transfer from NADH to NADP+ to proton translocation across the inner membrane in mitochondria and the cytoplasmic membrane in bacteria. The enzyme is composed of three parts. Domain I (dI) and domain III (dIII) are water soluble and contain the binding sites for NAD(H) and NADP(H), respectively; domain II (dII) spans the membrane. In the present investigation, dI from Rhodospirillum rubrum (rrI) and Escherichia coli (ecI), and dIII from R. rubrum (rrIII) and E. coli (ecIII) were overexpressed in E. coli and subsequently purified. Also, a preparation of a partially degraded E. coli transhydrogenase (ecbeta) was examined. Catalytic activities were analyzed in various dI+dIII and dI+ecbeta combinations. The abilities of the different dI+dIII combinations to catalyze cyclic transhydrogenation, i.e., the reduction of AcPyAD+ by NADH mediated via tightly bound NADP(H) in dIII, varied in the order: rrI+ecIII approximately rrI+rrIII > rrI+ecbeta >> ecI+ecIII; no measurable activities for ecI+rrIII and ecI+ecbeta were detected. Thus, rrI has a much greater apparent affinity than ecI for ecIII or rrIII or ecbeta. The pH dependences of the cyclic reaction seem to be determined by scalar protonation events on dI, both in rrI+rrIII and ecI+ecIII mixtures as well as in the wild-type R. rubrum and possibly in the E. coli enzyme. Higher reverse activities for rrI+ecbeta than for rrI+ecIII confirmed the regulatory role of dII for the association and dissociation rates of NADP(H).
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Affiliation(s)
- O Fjellström
- School of Biochemistry, University of Birmingham, UK
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41
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Gupta S, Quirk PG, Venning JD, Slade J, Bizouarn T, Grimley RL, Cotton NP, Jackson JB. Mutation of amino acid residues in the mobile loop region of the NAD(H)-binding domain of proton-translocating transhydrogenase. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1409:25-38. [PMID: 9804876 DOI: 10.1016/s0005-2728(98)00146-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The effects of single amino acid substitutions in the mobile loop region of the recombinant NAD(H)-binding domain (dI) of transhydrogenase have been examined. The mutations lead to clear assignments of well-defined resonances in one-dimensional 1H-NMR spectra. As with the wild-type protein, addition of NADH, or higher concentrations of NAD+, led to broadening and some shifting of the well-defined resonances. With many of the mutant dI proteins more nucleotide was required for these effects than with wild-type protein. Binding constants of the mutant proteins for NADH were determined by equilibrium dialysis and, where possible, by NMR. Generally, amino acid changes in the mobile loop region gave rise to a 2-4-fold increase in the dI-nucleotide dissociation constants, but substitution of Ala236 for Gly had a 10-fold effect. The mutant dI proteins were reconstituted with dI-depleted bacterial membranes with apparent docking affinities that were indistinguishable from that of wild-type protein. In the reconstituted system, most of the mutants were more inhibited in their capacity to perform cyclic transhydrogenation (reduction of acetyl pyridine adenine dinucleotide, AcPdAD+, by NADH in the presence of NADP+) than in either the simple reduction of AcPdAD+ by NADPH, or the light-driven reduction of thio-NADP+ by NADH, which suggests that they are impaired at the hydride transfer step. A cross-peak in the 1H-1H nuclear Overhauser enhancement spectrum of a mixture of wild-type dI and NADH was assigned to an interaction between the A8 proton of the nucleotide and the betaCH3 protons of Ala236. It is proposed that, following nucleotide binding, the mobile loop folds down on to the surface of the dI protein, and that contacts, especially from Tyr235 in a Gly-Tyr-Ala motif with the adenosine moiety of the nucleotide, set the position of the nicotinamide ring of NADH close to that of NADP+ in dIII to effect direct hydride transfer.
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Affiliation(s)
- S Gupta
- School of Biochemistry, University of Birmingham, Edgbaston B15 2TT, UK
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42
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Rydström J, Hu X, Fjellström O, Meuller J, Zhang J, Johansson C, Bizouarn T. Domains, specific residues and conformational states involved in hydride ion transfer and proton pumping by nicotinamide nucleotide transhydrogenase from Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1365:10-6. [PMID: 9693716 DOI: 10.1016/s0005-2728(98)00038-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Nicotinamide nucleotide transhydrogenase constitutes a proton pump which links the NAD(H) and NADP(H) pools in the cell by catalyzing a reversible reduction of NADP+ by NADH. The recent cloning and characterization of several proton-pumping transhydrogenases show that they share a number of features. They are composed of three domains, i.e., the hydrophilic domains I and III containing the NAD(H)- and NADP(H)-binding sites, respectively, and domain II containing the transmembrane and proton-conducting region. When expressed separately, the two hydrophilic domains interact directly and catalyze hydride transfer reactions similar to those catalyzed by the wild-type enzyme. An extensive mutagenesis program has established several amino acid residues as important for both catalysis and proton pumping. Conformational changes mediating the redox-driven proton pumping by the enzyme are being characterized. With the cloned, well-characterized and easily accessible transhydrogenases from E. coli and Rhodospirillum rubrum at hand, the overall aim of the transhydrogenase research, the understanding of the conformationally driven proton pumping mechanism, is within reach.
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Affiliation(s)
- J Rydström
- Department of Chemistry, Göteborg University, Sweden
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43
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Jackson JB, Quirk PG, Cotton NP, Venning JD, Gupta S, Bizouarn T, Peake SJ, Thomas CM. Interdomain hydride transfer in proton-translocating transhydrogenase. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1365:79-86. [PMID: 9693725 DOI: 10.1016/s0005-2728(98)00046-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We describe the use of the recombinant, nucleotide-binding domains (domains I and III) of transhydrogenase to study structural, functional and dynamic features of the protein that are important in hydride transfer and proton translocation. Experiments on the transient state kinetics of the reaction show that hydride transfer takes place extremely rapidly in the recombinant domain I:III complex, even in the absence of the membrane-spanning domain II. We develop the view that proton translocation through domain II is coupled to changes in the binding characteristics of NADP+ and NADPH in domain III. A mobile loop region which emanates from the surface of domain I, and which interacts with NAD+ and NADH during nucleotide binding has been studied by NMR spectroscopy and site-directed mutagenesis. An important role for the loop region in the process of hydride transfer is revealed.
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Affiliation(s)
- J B Jackson
- School of Biochemistry, University of Birmingham, Edgbaston, UK.
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44
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Grimley RL, Quirk PG, Bizouarn T, Thomas CM, Jackson JB. Role of methionine-239, an amino acid residue in the mobile-loop region of the NADH-binding domain (domain I) of proton-translocating transhydrogenase. Biochemistry 1997; 36:14762-70. [PMID: 9398196 DOI: 10.1021/bi971832l] [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: 02/05/2023]
Abstract
Transhydrogenase couples the transfer of hydride equivalents between NAD(H) and NADP(H) to proton translocation across a membrane. The one-dimensional proton NMR spectrum of the recombinant NAD(H)-binding domain (domain I) of transhydrogenase from Rhodospirillum rubrum reveals well-defined resonances, several of which arise from a mobile loop at the protein surface. Four have been assigned to Met residues (MetA-MetD). Substitution of Met239 with either Ile (dI.M239I) or Phe (dI.M239F) resulted in loss of MetA from the NMR spectrum. Broadening and shifting of the mobile loop resonances consequent on NAD(H) binding indicate that the loop closes down on the protein surface. More NAD(H) had to be added to mutant domain I than to wild type to give comparable resonance broadening. The Kd of domain I for NADH, measured by equilibrium dialysis, was increased about three-fold by the Met239 mutations. Mutant and wild-type domain I were reconstituted with domain I-depleted membranes from R. rubrum, and with recombinant domain III of transhydrogenase. With membranes, the Km for acetylpyridine adenine dinucleotide during reverse transhydrogenation was 5x and > 6x greater in dI.M239I and dI.M239F, respectively, than in wild-type. Cyclic transhydrogenation (in membranes and the recombinant system) was substantially more inhibited (70% in dI.M239I, and 84% in dI.M239F) than either forward or reverse transhydrogenation. The docking affinities of dI.M239I and dI.M239F to the depleted membranes were similar to those of wild-type. It is concluded that Met239 is MetA in the mobile loop of domain I, and that in proteins with amino acid substitutions at this position, the binding affinity of NAD(H) is decreased, and the hydride transfer step is inhibited.
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Affiliation(s)
- R L Grimley
- School of Biochemistry, University of Birmingham, Edgbaston, U.K
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45
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Bizouarn T, Stilwell S, Venning J, Cotton NP, Jackson JB. The pH dependences of reactions catalyzed by the complete proton-translocating transhydrogenase from Rhodospirillum rubrum, and by the complex formed from its recombinant nucleotide-binding domains. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1322:19-32. [PMID: 9398076 DOI: 10.1016/s0005-2728(97)00065-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Transhydrogenase couples the translocation of protons across a membrane to the transfer of reducing equivalents between NAD(H) and NADP(H). Using transhydrogenase from Rhodospirillum rubrum we have examined the pH dependences of the 'forward' and 'reverse' reactions, and of the 'cyclic' reaction (NADP(H)-dependent reduction of the analogue, acetyl pyridine adenine dinucleotide, by NADH). In the case of the membrane-bound protein in chromatophores, the imposition of a protonmotive force through the action of the light-driven electron-transport system, stimulated forward transhydrogenation, inhibited reverse transhydrogenation, but had no effect on the cyclic reaction. The differential response at a range of pH values provides evidence that hydride transfer per se is not coupled to proton translocation and supports the view that energy transduction occurs at the level of NADP(H) binding. Chromatophore transhydrogenase and the detergent-dispersed enzyme both have bell-shaped pH dependences for forward and reverse transhydrogenation. The cyclic reaction, however, is rapid at low and neutral pH, and is attenuated only at high pH. A mixture of recombinant purified NAD(H)-binding domain I, and NADP(H)-binding domain III, of R. rubrum transhydrogenase carry out the cyclic reaction with a similar pH profile to that of the complete enzyme, but the forward and reverse reactions were much less pH dependent. The rates of release of NADP+ and of NADPH from isolated domain III were pH independent. The results are consistent with a model for transhydrogenation, in which proton binding from one side of the membrane is consequent upon the binding of NADP+ to the enzyme, and then proton release on the other side of the membrane precedes NADPH release.
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Affiliation(s)
- T Bizouarn
- School of Biochemistry, University of Birmingham, Edgbaston, UK
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46
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Venning JD, Grimley RL, Bizouarn T, Cotton NP, Jackson JB. Evidence that the transfer of hydride ion equivalents between nucleotides by proton-translocating transhydrogenase is direct. J Biol Chem 1997; 272:27535-8. [PMID: 9346886 DOI: 10.1074/jbc.272.44.27535] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The molecular masses of the purified, recombinant nucleotide-binding domains (domains I and III) of transhydrogenase from Rhodospirillum rubrum were determined by electrospray mass spectrometry. The values obtained, 40,273 and 21,469 Da, for domains I and III, respectively, are similar to those estimated from the amino acid sequences of the proteins. Evidently, there are no prosthetic groups or metal centers that can serve as reducible intermediates in hydride transfer between nucleotides bound to these proteins. The transient-state kinetics of hydride transfer catalyzed by mixtures of recombinant domains I and III were studied by stopped-flow spectrophotometry. The data indicate that oxidation of NADPH, bound to domain III, and reduction of acetylpyridine adenine dinucleotide (an NAD+ analogue), bound to domain I, are simultaneous and very fast. The transient-state reaction proceeds as a biphasic burst of hydride transfer before establishment of a steady state, which is limited by slow release of NADP+. Hydride transfer between the nucleotides is evidently direct. This conclusion indicates that the nicotinamide rings of the nucleotides are in close apposition during the hydride transfer reaction, and it imposes firm constraints on the mechanism by which transhydrogenation is linked to proton translocation.
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Affiliation(s)
- J D Venning
- School of Biochemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
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47
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Fjellström O, Johansson C, Rydström J. Structural and catalytic properties of the expressed and purified NAD(H)- and NADP(H)-binding domains of proton-pumping transhydrogenase from Escherichia coli. Biochemistry 1997; 36:11331-41. [PMID: 9298952 DOI: 10.1021/bi970958f] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Proton-pumping nicotinamide nucleotide transhydrogenase from Escherichia coli contains three domains: the hydrophilic domains I and III harbor the binding sites for NAD(H) and NADP(H), respectively, and domain II represents the membrane-spanning region. Proton translocation involves primarily domain II but possibly also domain III, which contains the essential betaAsp392 residue. In the present investigation, the major portions of domain I (EcTHSalpha1 and EcTHSalpha2) and domain III (EcTHSbeta1) were overexpressed in E. coli and purified therefrom. EcTHSbeta1 was purified mainly in its holoform containing approximately 95% NADP+ and 5% NADPH. When combined, EcTHSalpha1/EcTHSalpha2 and EcTHSbeta1 were catalytically active, indicating native-like structures. Due to the lack of structural information and its possible role in proton pumping, EcTHSbeta1 was primarily characterized. Substrate-binding characteristics and conformational changes were investigated by fluorescence and CD. Fluorescence arising from the single betaTrp415 of EcTHSbeta1 was quenched upon binding of NADPH by resonance energy transfer, an effect that provides an important tool for investigating substrate interactions with this domain and the determination of Kd values. The apparent relative binding affinity for NADPH was found to be about 50 times higher than that for NADP+. Circular dichroism was used to estimate secondary structure content and for conformational analysis of EcTHSbeta1 in the absence and presence of added substrates at various temperatures. Results show that domain III complexed with NADPH or NADP+ adopts different conformations. Isoelectric focusing and native gel electrophoresis experiments support this finding. It is proposed that these structural differences play a central role in a conformationally-driven proton pump mechanism of the intact enzyme.
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Affiliation(s)
- O Fjellström
- Department of Biochemistry and Biophysics, Göteborg University and Chalmers University of Technology, S-413 90 Göteborg, Sweden
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48
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Bizouarn T, Grimley R, Diggle C, Thomas CM, Jackson JB. Mutations at tyrosine-235 in the mobile loop region of domain I protein of transhydrogenase from Rhodospirillum rubrum strongly inhibit hydride transfer. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1320:265-74. [PMID: 9230921 DOI: 10.1016/s0005-2728(97)00030-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Transhydrogenase from mitochondrial and bacterial membranes couples proton translocation to hydride transfer between NAD(H) and NADP(H). The enzyme has three domains, of which domains I and III protrude from the membrane. These possess the NAD(H)- and NADP(H)-binding sites, respectively, whereas domain II spans the membrane. In domain I there is a mobile loop which emanates from the surface of the protein, but which closes down upon NAD(H) binding. In this report we show that the NADP(H)-dependent reduction of acetylpyridine adenine dinucleotide by NADH catalysed by Rhodospirillum rubrum transhydrogenase has 'ping-pong' kinetics, confirming that the reaction is cyclic. We then describe the kinetic and thermodynamic properties of mutants of recombinant domain I protein from the R. rubrum enzyme, in which Tyr-235 in the mobile loop has been substituted with Phe or Asn residues (dI.Y235F and dI.Y235N, respectively). (1) Equilibrium dialysis measurements show that dI.Y235F and dI.Y235N bind NADH more weakly than wild-type domain I protein (the Kd increases twofold and fourfold, respectively). (2) Reverse transhydrogenation rates (in steady state) of domain I-depleted membrane vesicles reconstituted with either dI.Y235F or dI.Y235N are inhibited by about 50% and 78%, respectively, relative to those obtained in reconstitutions with wild-type domain I protein. (3) Reverse transhydrogenation rates (in steady state) of mixtures of recombinant domain III protein and either dI.Y235F or dI.Y235N are inhibited only by about 10% and 20%, respectively, relative to those obtained in mixtures with wild-type protein. (4) Forward transhydrogenation rates (in both the complete enzyme and in domain I:III complexes) are inhibited even less by the mutations than the reverse reactions. (5) In contrast with (1), (2) and (3), cyclic transhydrogenation was strongly inhibited in both the reconstituted membrane system and in the recombinant domain I:III complexes (only 7-8% activity remains with dI.Y235F, and only 2-3% with dI.Y235N). It was recently established that, in contrast to forward and reverse transhydrogenation, the cyclic reaction is substantially limited by the rate of hydride transfer. It is therefore concluded that mutations at Tyr-235 in the mobile loop severely disrupt the hydride transfer step in the catalytic reaction of transhydrogenase.
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Affiliation(s)
- T Bizouarn
- School of Biochemistry, University of Birmingham, Edgbaston, UK
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Stilwell SN, Bizouarn T, Jackson JB. The reduction of acetylpyridine adenine dinucleotide by NADH: is it a significant reaction of proton-translocating transhydrogenase, or an artefact? BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1320:83-94. [PMID: 9186780 DOI: 10.1016/s0005-2728(97)00016-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Transhydrogenase is a proton pump. It has separate binding sites for NAD+/NADH (on domain I of the protein) and for NADP+/NADPH (on domain III). Purified, detergent-dispersed transhydrogenase from Escherichia coli catalyses the reduction of the NAD+ analogue, acetylpyridine adenine dinucleotide (AcPdAD+), by NADH at a slow rate in the absence of added NADP+ or NADPH. Although it is slow, this reaction is surprising, since transhydrogenase is generally thought to catalyse hydride transfer between NAD(H)--or its analogues and NADP(H)--or its analogues, by a ternary complex mechanism. It is shown that hydride transfer occurs between the 4A position on the nicotinamide ring of NADH and the 4A position of AcPdAD+. On the basis of the known stereospecificity of the enzyme, this eliminates the possibilities of transhydrogenation(a) from NADH in domain I to AcPdAD+ wrongly located in domain III; and (b) from NADH wrongly located in domain III to AcPdAD+ in domain I. In the presence of low concentrations of added NADP+ or NADPH, detergent-dispersed E. coli transhydrogenase catalyses the very rapid reduction of AcPdAD+ by NADH. This reaction is cyclic; it takes place via the alternate oxidation of NADPH by AcPdAD+ and the reduction of NADP+ by NADH, while the NADPH and NADP+ remain tightly bound to the enzyme. In the present work, it is shown that the rate of the cyclic reaction and the rate of reduction of AcPdAD+ by NADH in the absence of added NADP+/NADPH, have similar dependences on pH and on MgSO4 concentration and that they have a similar kinetic character. It is therefore suggested that the reduction of AcPdAD+ by NADH is actually a cyclic reaction operating, either with tightly bound NADP+/NADPH on a small fraction (< 5%) of the enzyme, or with NAD+/NADH (or AcPdAD+/AcPdADH) unnaturally occluded within the domain III site. Transhydrogenase associated with membrane vesicles (chromatophores) of Rhodospirillum rubrum also catalyses the reduction of AcPdAD+ by NADH in the absence of added NADP+/NADPH. When the chromatophores were stripped of transhydrogenase domain I, that reaction was lost in parallel with 'normal reverse' transhydrogenation (e.g., the reduction of AcPdAD+ by NADPH). The two reactions were fully recovered upon reconstitution with recombinant domain I protein. However, after repeated washing of the domain I-depleted chromatophores, reverse transhydrogenation activity (when assayed in the presence of domain I) was retained, whereas the reduction of AcPdAD+ by NADH declined in activity. Addition of low concentrations of NADP+ or NADPH always supported the same high rate of the NADH-->AcPdAD+ reaction independently of how often the membranes were washed. It is concluded that, as with the purified E. coli enzyme, the reduction of AcPdAD+ by NADH in chromatophores is a cyclic reaction involving nucleotides that are tightly bound in the domain III site of transhydrogenase. However, in the case of R. rubrum membranes it can be shown with some certainty that the bound nucleotides are NADP+ or NADPH. The data are thus adequately explained without recourse to suggestions of multiple nucleotide-binding sites on transhydrogenase.
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Affiliation(s)
- S N Stilwell
- School of Biochemistry, University of Birmingham, Edgbaston, UK
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Diggle C, Bizouarn T, Cotton NP, Jackson JB. Properties of the purified, recombinant, NADP(H)-binding domain III of the proton-translocating nicotinamide nucleotide transhydrogenase from Rhodospirillum rubrum. EUROPEAN JOURNAL OF BIOCHEMISTRY 1996; 241:162-70. [PMID: 8898902 DOI: 10.1111/j.1432-1033.1996.0162t.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Transhydrogenase comprises three domains. Domains I and III are peripheral to the membrane and possess the NAD(H)- and NADP(H)-binding sites, respectively, and domain II spans the membrane. Domain III of transhydrogenase from Rhodospirillum rubrum was expressed at high levels in Escherichia coli, and purified. The purified protein was associated with substoichiometric quantities of tightly bound NADP+ and NADPH. Fluorescence spectra of the domain III protein revealed emissions due to Tyr residues. Energy transfer was detected between Tyr residue(s) and the bound NADPH, indicating that the amino acid residue(s) and the nucleotide are spatially close. The rate constants for NADP+ release and NADPH release from domain III were 0.03 s-1 and 5.6 x 10(4) s-1, respectively. In the absence of domain II a mixture of the recombinant domain III protein, plus the previously described recombinant domain I protein, catalysed reduction of acetylpyridine-adenine dinucleotide (AcPdAD+) by NADPH (reverse transhydrogenation) at a rate that was limited by the release of NADP+ from domain III. Similarly, the mixture catalysed reduction of thio-NADP+ by NADH (forward transhydrogenation) at a rate limited by release of thio-NADPH from domain III. The mixture also catalysed very rapid reduction of AcPdAD+ by NADH, probably by way of a cyclic reaction mediated by the tightly bound NADP(H). Measurement of the rates of the transhydrogenation reactions during titrations of domain I with domain III and vice versa indicated (a) that during reduction of AcPdAD+ by NADPH, a single domain I protein can visit and transfer H equivalents to about 60 domain III proteins during the time taken for a single domain III to release its NADP+, whereas (b) the cyclic reaction is rapid on the timescale of formation and break-down of the domain I. III complex. The rate of the hydride transfer reaction was similar in the domain I.III complex to that in the complete membrane-bound transhydrogenase, but the rates of forward and reverse transhydrogenation were much slower in the I.III complex due to the greatly decreased rates of release of NADP+ and NADPH. It is concluded that, in the complete enzyme, conformational changes in the membrane-spanning domain II, which result from proton translocation, lead to changes in the binding affinity of domain III for NADP+ and for NADPH.
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Affiliation(s)
- C Diggle
- School of Biochemistry, University of Birmingham, UK
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