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Scharnagl C, Reif M, Friedrich J. Local compressibilities of proteins: comparison of optical experiments and simulations for horse heart cytochrome-c. Biophys J 2005; 89:64-75. [PMID: 15834001 PMCID: PMC1366563 DOI: 10.1529/biophysj.104.057265] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2004] [Accepted: 04/01/2005] [Indexed: 11/18/2022] Open
Abstract
Spectroscopy with probe molecules yields local information on the environment of the probe. In this article we compare local compressibilities of cytochrome-c as obtained from molecular dynamics simulations with experimental results as obtained from spectroscopic measurements. The simulations show that the protein-core around the heme is much less compressible in a glycerol/water solvent than in pure water. The pocket is also much less compressible than the protein as a whole, although the compressibility of the water inside the rather incompressible protein-core is almost liquidlike. We show that the local compressibility values capture the collective correlations of local volume fluctuations with volume fluctuations in the surrounding protein-solvent system. The decoupling of the volume fluctuations of the core from the solvent shell explains the reduction of the heme-core-compressibility in glycerol/water solvent. This decoupling could be traced back to the suppression of the exchange between pocket-water and hydration-shell-water upon addition of glycerol as co-solvent.
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Affiliation(s)
- Christina Scharnagl
- Physik-Department E14, Lehrstuhl für Physik Weihenstephan, Technische Universität München, Freising, Germany.
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2
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Croney JC, Helms MK, Jameson DM, Larsen RW. Conformational dynamics and temperature dependence of photoinduced electron transfer within self-assembled coproporphyrin:cytochrome c complexes. Biophys J 2003; 84:4135-43. [PMID: 12770916 PMCID: PMC1302992 DOI: 10.1016/s0006-3495(03)75138-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2002] [Accepted: 01/28/2003] [Indexed: 10/21/2022] Open
Abstract
The focus of the present study is to better understand the complex factors influencing intermolecular electron transfer (ET) in biological molecules using a model system involving free-base coproporphyrin (COP) complexed with horse heart cytochrome c (Cc). Coproporphyrin exhibits bathochromic shifts in both the Soret and visible absorption bands in the presence of Cc and an absorption difference titration reveals a 1:1 complex with an association constant of 2.63 +/- 0.05 x 10(5) M(-1). At 20 degrees C, analysis of time-resolved fluorescence data reveals two lifetime components consisting of a discrete lifetime at 15.0 ns (free COP) and a Gaussian distribution of lifetimes centered at 2.8 ns (representing (1)COP --> Cc ET). Temperature-dependent, time-resolved fluorescence data demonstrate a shift in singlet lifetime as well as changes in the distribution width (associated with the complex). By fitting these data to semiclassical Marcus theory, the reorganizational energy (lambda) of the singlet state electron transfer was calculated to be 0.89 eV, consistent with values for other porphyrin/Cc intermolecular ET reactions. Using nanosecond transient absorption spectroscopy the temperature dependences of the forward and thermal back ET originating from triplet state were examined ((3)COP --> Cc ET). Fits of the temperature dependence of the rate constants to semiclassical Marcus theory gave lambda of 0.39 eV and 0.11 eV for the forward and back triplet ET, respectively (k(f) = (7.6 +/- 0.3) x 10(6) s(-1), k(b) = (2.4 +/- 0.3) x 10(5) s(-1)). The differing values of lambda for the forward and back triplet ET demonstrate that these ET reactions do not occur within a static complex. Comparing these results with previous studies of the uroporphyrin:Cc and tetrakis (4-carboxyphenyl)porphyrin:Cc complexes suggests that side-chain flexibility gives rise to the conformational distributions in the (1)COP --> Cc ET whereas differences in overall porphyrin charge regulates gating of the back ET reaction (reduced Cc --> COP(+)).
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Affiliation(s)
- John C Croney
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA
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3
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Körner M, Tregloan PA, Eldik RV. Outer-sphere electron-transfer between horse heart cytochrome c and anionic Cu(ii/i) complexes. Evidence for precursor formation and coordination sphere reorganization for electron transfer. Dalton Trans 2003. [DOI: 10.1039/b301693e] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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4
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Tremain SM, Kostić NM. Fate of the excited triplet state of zinc cytochrome c in the presence of iron(III), iron(II), iron-free, and heme-free forms of cytochrome c. Inorganica Chim Acta 2000. [DOI: 10.1016/s0020-1693(00)00012-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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5
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Avila A, Gregory BW, Niki K, Cotton TM. An Electrochemical Approach to Investigate Gated Electron Transfer Using a Physiological Model System: Cytochrome c Immobilized on Carboxylic Acid-Terminated Alkanethiol Self-Assembled Monolayers on Gold Electrodes. J Phys Chem B 2000. [DOI: 10.1021/jp992591p] [Citation(s) in RCA: 226] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Albert Avila
- Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Chemistry, Illinois State University, Normal, Illinois 61790
| | - Brian W. Gregory
- Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Chemistry, Illinois State University, Normal, Illinois 61790
| | - Katsumi Niki
- Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Chemistry, Illinois State University, Normal, Illinois 61790
| | - Therese M. Cotton
- Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Chemistry, Illinois State University, Normal, Illinois 61790
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6
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Laberge M, Köhler M, Vanderkooi JM, Friedrich J. Sampling field heterogeneity at the heme of c-type cytochromes by spectral hole burning spectroscopy and electrostatic calculations. Biophys J 1999; 77:3293-304. [PMID: 10585951 PMCID: PMC1300600 DOI: 10.1016/s0006-3495(99)77160-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
We report on a comparative investigation of the heme pocket fields of two Zn-substituted c-type cytochromes-namely yeast and horse heart cytochromes c-using a combination of hole burning Stark spectroscopy and electrostatic calculations. The spectral hole burning experiments are consistent with different pocket fields experienced at the hemes of the respective cytochromes. In the case of horse heart Zn-cytochrome c, two distinguishable electronic origins with different electrostatic properties are observed. The yeast species, on the other hand, displays a single electronic origin. Electrostatic calculations and graphics modeling using the linearized finite-difference Poisson-Boltzmann equation performed at selected time intervals on nanosecond-molecular dynamics trajectories show that the hemes of the respective cytochromes sample different potentials as they explore conformational space. The electrostatic potentials generated by the protein matrix at the heme show different patterns in both cytochromes, and we suggest that the cytochromes differ by the number of "electrostatic substates" that they can sample, thus accounting for the different spectral populations observed in the two cytochromes.
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Affiliation(s)
- M Laberge
- Institute of Biophysics, Semmelweis University of Medicine, H-1088 Budapest, Hungary
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7
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Larsen RW, Helms MK, Everett WR, Jameson DM. Ground-and Excited-State Characterization of an Electrostatic Complex between Tetrakis-(4-Sulfonatophenyl)porphyrin and 16-Pyrimidinium Crown-4. Photochem Photobiol 1999. [DOI: 10.1111/j.1751-1097.1999.tb03308.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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8
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Ivković-Jensen MM, Ullmann GM, Crnogorac MM, Ejdebäck M, Young S, Hansson O, Kostić NM. Comparing the rates and the activation parameters for the forward reaction between the triplet state of zinc cytochrome c and cupriplastocyanin and the back reaction between the zinc cytochrome c cation radical and cuproplastocyanin. Biochemistry 1999; 38:1589-97. [PMID: 9931026 DOI: 10.1021/bi9817156] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This is a comparative study of the photoinduced (so-called forward) electron-transfer reaction 3Zncyt/pc(II) --> Zncyt+/pc(I), between the triplet state of zinc cytochrome c (3Zncyt) and cupriplastocyanin [pc(II)], and the thermal (so-called back) electron-transfer reaction Zncyt+/pc(I) --> Zncyt/pc(II), between the cation (radical) of zinc cytochrome c (Zncyt+) and cuproplastocyanin [pc(I)], which follows it. Both reactions occur between associated (docked) reactants, and the respective unimolecular rate constants are kF and kB. Our previous studies showed that the forward reaction is gated by a rearrangement of the diprotein complex. Now we examine the back reaction and complare the two. We study the effects of temperature (in the range 273.3-302.9 K) and viscosity (in the range 1.00-17.4 cP) on the rate constants and determine enthalpies (DeltaH), entropies (DeltaS), and free energies (DeltaG) of activation. We compare wild-type spinach plastocyanin, the single mutants Tyr83Leu and Glu59Lys, and the double mutant Glu59Lys/Glu60Gln. The rate constant kB for wild-type spinach plastocyanin and its mutants markedly depends on viscosity, an indication that the back reaction is also gated. The activation parameters DeltaH and DeltaS show that the forward and back reactions have similar mechanisms, involving a rearrangement of the diprotein complex from the initial binding configuration to the reactive configuration. The rearrangements of the complexes 3Zncyt/pc(II) and Zncyt+/pc(I) that gate their respective reactions are similar but not identical. Since the back reaction of all plastocyanin variants is faster than the forward reaction, the difference in free energy between the docking and the reactive configuration is smaller for the back reaction than for the forward reaction. This difference is explained by the change in the electrostatic potential on the plastocyanin surface as Cu(II) is reduced to Cu(I). It is the smaller DeltaH that makes DeltaG smaller for the back reaction than for the forward reaction.
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9
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Ivković-Jensen MM, Ullmann GM, Young S, Hansson O, Crnogorac MM, Ejdebäck M, Kostić NM. Effects of single and double mutations in plastocyanin on the rate constant and activation parameters for the rearrangement gating the electron-transfer reaction between the triplet state of zinc cytochrome c and cupriplastocyanin. Biochemistry 1998; 37:9557-69. [PMID: 9649339 DOI: 10.1021/bi9802871] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The unimolecular rate constant for the photoinduced electron-transfer reaction 3Zncyt/pc(II) --> Zncyt+/pc(I) within the electrostatic complex of zinc cytochrome c and spinach cupriplastocyanin is kF. We report the effects on kF of the following factors, all at pH 7.0: 12 single mutations on the plastocyanin surface (Leu12Asn, Leu12Glu, Leu12Lys, Asp42Asn, Asp42Lys, Glu43Asn, Glu59Gln, Glu59Lys, Glu60Gln, Glu60Lys, Gln88Glu, and Gln88Lys), the double mutation Glu59Lys/Glu60Gln, temperature (in the range 273.3-302.9 K), and solution viscosity (in the range 1. 00-116.0 cP) at 283.2 and 293.2 K. We also report the effects of the plastocyanin mutations on the association constant (Ka) and the corresponding free energy of association (DeltaGa) with zinc cytochrome c at 298.2 K. Dependence of kF on temperature yielded the activation parameters DeltaH, DeltaS, and DeltaG. Dependence of kF on solution viscosity yielded the protein friction and confirmed the DeltaG values determined from the temperature dependence. The aforementioned intracomplex reaction is not a simple electron-transfer reaction because donor-acceptor electronic coupling (HAB) and reorganizational energy (lambda), obtained by fitting of the temperature dependence of kF to the Marcus equation, deviate from the expectations based on precedents and because kF greatly depends on viscosity. This last dependence and the fact that certain mutations affect Ka but not kF are two lines of evidence against the mechanism in which the electron-transfer step is coupled with the faster, but thermodynamically unfavorable, rearrangement step. The electron-transfer reaction is gated by the slower, and thus rate determining, structural rearrangement of the diprotein complex; the rate constant kF corresponds to this rearrangement. Isokinetic correlation of DeltaH and DeltaS parameters and Coulombic energies of the various configurations of the Zncyt/pc(II) complex consistently show that the rearrangement is a facile configurational fluctuation of the associated proteins, qualitatively the same process regardless of the mutations in plastocyanin. Correlation of kF with the orientation of the cupriplastocyanin dipole moment indicates that the reactive configuration of the diprotein complex involves the area near the residue 59, between the upper acidic cluster and the hydrophobic patch. Kinetic effects and noneffects of plastocyanin mutations show that the rearrangement from the initial (docking) configuration, which involves both acidic clusters, to the reactive configuration does not involve the lower acidic cluster and the hydrophobic patch but involves the upper acidic cluster and the area near the residue 88.
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10
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Ivković-Jensen MM, Kostić NM. Effects of viscosity and temperature on the kinetics of the electron-transfer reaction between the triplet state of zinc cytochrome c and cupriplastocyanin. Biochemistry 1997; 36:8135-44. [PMID: 9201962 DOI: 10.1021/bi970327l] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
This is a study of the effects of viscosity (in the range of 0.8-790 cP), of temperature (in the range of 260.7-307.7 K), and of ionic strength (in the range of 2.5-20.0 mM) on the kinetics of photoinduced electron-transfer reaction 3Zncyt/pc(II) --> Zncyt+/pc(I) within the electrostatic complex of zinc cytochrome c and cupriplastocyanin at pH 7.0. The unimolecular rate constant is kF. The apparent activation parameters DeltaH*, DeltaS*, and DeltaG* for this reaction were obtained in experiments with aqueous glycerol solutions having a constant composition. The interpolation of kF values obtained at the constant composition into the dependence of kF on temperature at constant viscosity gave the proper activation parameters, which agree with those obtained in experiments with solutions having a constant viscosity. This agreement validates the latter method, which is more efficient than the former, for determining activation parameters of processes that are modulated by viscosity. The smooth change in kF is governed by the change in viscosity, not in other properties of the solvent, and it does not depend on the choice of the viscosigen. Donor/acceptor electronic coupling (HAB) and reorganizational energy (lambda), obtained by fitting of the temperature dependence of kF to the Marcus equation, are consistent with true electron transfer and with electron transfer that is coupled to, or gated by, a preceding structural rearrangement of the diprotein complex 3Zncyt/pc(II). The fact that at very high viscosity kF approaches zero shows that the reaction is probably gated throughout the investigated range of viscosity. Kinetic effects and noneffects of ionic strength, viscosity, and thermodynamic driving force indicate, but do not prove, that the reaction under consideration is gated. The kinetic effect of viscosity is analyzed in terms of two models. Because ln kF is a nonlinear function of ln eta, protein friction has to be considered in the analysis of viscosity effects on kinetics.
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11
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Harris MR, Davis DJ, Durham B, Millett F. Temperature and viscosity dependence of the electron-transfer reaction between plastocyanin and cytochrome c labeled with a ruthenium(II) bipyridine complex. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1319:147-54. [PMID: 9131042 DOI: 10.1016/s0005-2728(96)00155-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The temperature and viscosity dependence of the photo-induced electron-transfer reaction between plastocyanin and cytochrome c labeled at Lys13 with Ru(4,4'-dicarboxybipyridine)(bipyridine)(2+)2 have been investigated. In these studies, a short pulse of 450 nm light was used to excite the ruthenium complex which was oxidatively quenched by the iron center of cytochrome c. The resulting Fe(II) cytochrome c was then rapidly reoxidized by plastocyanin. The reactions were investigated over a temperature range of 3.5 to 37 degrees C under low ionic strength conditions such that protein/protein complex formation was favored. The enthalpy of activation was 7 kcal mol-1 and the entropy of activation was -20 cal mol-1 K-1. Increasing the viscosity by the addition of sucrose up to 70% resulted in a 4-fold decrease in the rate constant for electron transfer. The overall results suggest a rate-limiting step that involves either dissociation of the dominant protein/protein complex or surface diffusion of the associated proteins.
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Affiliation(s)
- M R Harris
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville 72701, USA
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12
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Ye S, Shen C, Cotton TM, Kostić NM. Characterization of zinc-substituted cytochrome c by circular dichroism and resonance Raman spectroscopic methods. J Inorg Biochem 1997; 65:219-26. [PMID: 9025273 DOI: 10.1016/s0162-0134(97)00001-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Iron(III) in cytochrome c is replaced with zinc(II) by a modification of a method published by others, and the procedure is described in full detail. Three forms of cytochrome c-those containing iron(III), iron(II), and zinc(II)-are examined by circular dichroism spectroscopy and resonance Raman spectroscopy. Spectra of both kinds show that introduction of zinc(II) ions does not appreciably alter the overall structure and conformation of cytochrome c. Resonance Raman spectra indicate the size of the porphyrin "core" that is inconsistent with six-coordination and consistent with five-coordination. Unlike the iron(III) and iron(II) ions, which are bound to two axial ligands (His 18 and Met 80), the zinc(II) ion in cytochrome c seems to be bound to only one, most probably His 18. Evidence pertaining to the question of axial coordination is discussed.
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Affiliation(s)
- S Ye
- Department of Chemistry, Iowa State University, Ames 50011-3111, USA
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13
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Shen C, Kostić NM. Kinetics of Photoinduced Electron-Transfer Reactions within Sol-Gel Silica Glass Doped with Zinc Cytochrome c. Study of Electrostatic Effects in Confined Liquids. J Am Chem Soc 1997. [DOI: 10.1021/ja961867t] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Chengyu Shen
- Contribution from the Department of Chemistry, Iowa State University, Ames, Iowa 50011
| | - Nenad M. Kostić
- Contribution from the Department of Chemistry, Iowa State University, Ames, Iowa 50011
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14
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Crnogorac MM, Shen C, Young S, Hansson O, Kostić NM. Effects of mutations in plastocyanin on the kinetics of the protein rearrangement gating the electron-transfer reaction with zinc cytochrome c. Analysis of the rearrangement pathway. Biochemistry 1996; 35:16465-74. [PMID: 8987979 DOI: 10.1021/bi961914u] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
We study, by flash kinetic spectrophotometry on the microsecond time scale, the effects of ionic strength and viscosity on the kinetics of oxidative quenching of the triplet state of zinc cytochrome c (3Zncyt) by the wild-type form and the following nine mutants of cupriplastocyanin: Leu12Glu, Leu12Asn, Phe35Tyr, Gln88Glu, Tyr83Phe, Tyr83His, Asp42Asn, Glu43Asn, and the double mutant Glu59Lys/Glu60Gln. The unimolecular rate constants for the quenching reactions within the persistent diprotein complex, which predominates at low ionic strengths, and within the transient diprotein complex, which is involved at higher ionic strengths, are equal irrespective of the mutation. Evidently, the two complexes are the same. In both reactions, the rate-limiting step is rearrangement of the diprotein complex from a configuration optimal for docking to the one optimal for the subsequent electron-transfer step, which is fast. We investigate the effects of plastocyanin mutations on this rearrangement, which gates the overall electron-transfer reaction. Conversion of the carboxylate anions into amide groups in the lower acidic cluster (residues 42 and 43), replacement of Tyr83 with other aromatic residues, and mutations in the hydrophobic patch in plastocyanin do not significantly affect the rearrangement. Conversion of a pair of carboxylate anions into a cationic and a neutral residue in the upper acidic cluster (residues 59 and 60) impedes the rearrangement. Creation of an anion at position 88, between the upper acidic cluster and the hydrophobic patch, facilitates the rearrangement. The rate constant for the rearrangement smoothly decreases as the solution viscosity increases, irrespective of the mutation. Fittings of this dependence to the modified Kramers's equation and to an empirical equation show that zinc cytochrome c follows the same trajectory on the surfaces of all the plastocyanin mutants but that the obstacles along the way vary as mutations alter the electrostatic potential. Mutations that affect protein association (i.e., change the binding constant) do not necessarily affect the reaction between the associated proteins (i.e., the rate constant) and vice versa. All of the kinetic and thermodynamic effects and noneffects of mutations consistently indicate that in the protein rearrangement the basic patch of zinc cytochrome c moves from a position between the two acidic clusters to a position at or near the upper acidic cluster.
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Affiliation(s)
- M M Crnogorac
- Department of Chemistry, Iowa State University, Ames 50011, USA
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15
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Ivković-Jensen MM, Kostić NM. Effects of temperature on the kinetics of the gated electron-transfer reaction between zinc cytochrome c and plastocyanin. Analysis of configurational fluctuation of the diprotein complex. Biochemistry 1996; 35:15095-106. [PMID: 8942677 DOI: 10.1021/bi961608g] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
This is a study of the effects of temperature (in the range 273.3-307.7 K) and of ionic strength (in the range 2.5-100 mM) on the kinetics of photoinduced electron-transfer reaction 3Zncyt/pc(II)--> Zncyt+/pc(I) within the electrostatic complex of zinc cytochrome c and cupriplastocyanin at pH 7.0. In order to separate direct and indirect effects of temperature on the rate constants, viscosity of the solutions was fixed, at different values, by additions of sucrose. The activation parameters for the reaction within the preformed complex, at the low ionic strength, are delta H++ = 13 +/- 2 kJ/mol and delta S++ = -97 +/- 4 J/K mol. The activation parameters for the reaction within the encounter complex, at the higher ionic strength, are delta H++ = 13 +/- 1 kJ/mol and delta S++ = -96 +/- 3 J/K mol. Evidently, the two complexes are the same. The proteins associate similarly in the persistent and the transient complex, i.e., at different ionic strengths. In both complexes, however, electron transfer is gated by a rearrangement, as previous studies from this laboratory showed. Changes in the solution viscosity modulate this rearrangement by affecting delta H++, not delta S++. The activation parameters are analyzed by empirical methods. The thermodynamic parameters delta H and delta S for the formation of the complex Zncyt/pc(II) are determined and related to changes in hydrophilic and hydrophobic surfaces upon protein association in three configurations. A difference between the values of delta H for the configuration providing optimal electronic coupling between the redox sites and the configuration providing optimal docking equals the experimental value delta H++ = 13 kJ/mol for the rearrangement of the latter configuration into the former. Enthalpy of activation may reflect a change in the character of the exposed surface as the diprotein complex rearranges. Entropy of activation may reflect tightening of the contact between the associated proteins.
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16
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Bellelli A, Brzezinski P, Arese M, Cutruzzola F, Silvestrini MC, Brunori M. Electron transfer in zinc-reconstituted nitrite reductase from Pseudomonas aeruginosa. Biochem J 1996; 319 ( Pt 2):407-10. [PMID: 8912674 PMCID: PMC1217783 DOI: 10.1042/bj3190407] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
1. The catalytic cycle of the haem-containing nitrite reductase (NIR) from Pseudomonas aeruginosa involves electron transfer between the two prosthetic groups of the enzyme, the c-haem and the d1-haem; this reaction was shown to be slow by stopped-flow analysis. The recombinant enzyme, expressed in Pseudomonas putida, contains the c-haem but no d1-haem; we have reconstituted this protein with Zn-protoporphyrin IX in the place of the d1-haem. 2. Photoexcitation of Zn-NIR is followed by electron transfer from the triplet excited state of the Zn-porphyrin to the oxidized c-haem, with a rate constant of 7 x 10(5) s-1; since the intermediate with reduced c-haem is not significantly populated, we conclude that the back reaction is probably as fast. 3. Even taking into account that in the native NIR the driving force is close to zero, the rate constant for the c-->d1 electron transfer, estimated from our experiments, is still much higher than that observed by stopped flow (k = 0.3 s-1) using reduced azurin as the electron donor. This finding may be a direct kinetic indication that reduction of the d1-haem is associated with a substantial reorganization of the co-ordination of the metal, as shown by spectroscopy of the oxidized and reduced NIR.
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Affiliation(s)
- A Bellelli
- Department of Biochemical Sciences, University of Rome La Sapienza, Italy
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17
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Shen C, Kostić NM. Reductive Quenching of the Triplet State of Zinc Cytochrome c by the Hexacyanoferrate(II) Anion and by Conjugate Bases of Ethylenediaminetetraacetic Acid. Inorg Chem 1996. [DOI: 10.1021/ic9510270] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Chengyu Shen
- Department of Chemistry, Iowa State University, Ames, Iowa 50011
| | - Nenad M. Kostić
- Department of Chemistry, Iowa State University, Ames, Iowa 50011
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18
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Qin L, Kostić NM. Enforced interaction of one molecule of plastocyanin with two molecules of cytochrome c and an electron-transfer reaction involving the hydrophobic patch on the plastocyanin surface. Biochemistry 1996; 35:3379-86. [PMID: 8639487 DOI: 10.1021/bi9516586] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Laser flash photolysis is used to study the photoinduced electron-transfer reaction cyt(III)//pc(II) + 3Zncyt --> cyt(III)//pc(I) + Zincyt+ at pH 7.0 and 25 degrees. In the covalent (symbol//) complex cyt(III)//pc(II) the acidic patch in cupriplastocyanin is directly cross-linked to the basic patch in ferricytochrome c. The triplet state of zinc cytochrome c reduces the pc(II) moiety, not the cyt(III) moiety, of the covalent complex. The reaction is strictly bimolecular in the entire range of ionic strength studied, from 1.25 mM to 1.00 M. The two reactants interact only transiently, in a collisional complex, and do not form a persistent complex cyt(III)//pc(II)/Zncyt. Because noncovalent (symbol/) association of three separate protein molecules is far less probable than association of the covalent complex and another protein molecule, we conclude that, without the aid of covalent cross-links, one molecule of plastocyanin will not form a ternary complex with two molecules of cytochrome c, cyt/pc/cyt. Dependence of the rate constant on ionic strength is analyzed in terms of van Leeuwen theory of electrostatic interactions, which recognizes the importance of dipole moments of the proteins. This analysis shows that 3Zncyt reacts with the hydrophobic patch in the pc(II) moiety of the covalent complex cyt(III)//pc(II). At high ionic strength, at which electrostatic interactions are practically abolished, the blue copper site is reduced with approximately equal rates via the hydrophobic patch in the pc(II) moiety of the complex and via the acidic patch in free pc(II). This is evidence that the two distinct patches on the plastocyanin surface are comparable in their intrinsic "conductivity" for electrons coming to the copper site. Positively charged and electroneutral redox partners tend to react at the acidic patch (although not necessarily at the initial docking site in this broad patch) for electrostatic, not electronic, reasons. Earlier theorectical studies disagreed about the relative electronic conductivities of the two patches. This experimental study corroborates very recent theoretical studies that found the two patches to be comparable in the efficiency of electron transfer.
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Affiliation(s)
- L Qin
- Department of Chemistry, Iowa State University, Ames 50011, USA
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Angiolillo PJ, Vanderkooi JM. Electron paramagnetic resonance of the excited triplet state of metal-free and metal-substituted cytochrome c. Biophys J 1995; 68:2505-18. [PMID: 7647253 PMCID: PMC1282160 DOI: 10.1016/s0006-3495(95)80433-9] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The photoactivated metastable triplate states of the porphyrin (free-base, i.e., metal-free) zinc and tin derivatives of horse cytochrome c were investigated using electron paramagnetic resonance. Zero-field splitting parameters, line shape, and Jahn-Teller distortion in the temperature range 3.8-150 K are discussed in terms of porphyrin-protein interactions. The zero-field splitting parameters D for the free-base, Zn and Sn derivatives are 465 x 10(-4), 342 x 10(-4) and 353 x 10(-4) cm-1, respectively, and are temperature invariant over the temperature ranges studied. AN E value at 4 K of 73 x 10(-4) cm-1 was obtained for Zn cytochrome c, larger than any previously found for Zn porphyrins derivatives of hemeproteins, showing that the heme site of cytochrome c imposes an asymmetric field. Though the E value for Zn cytochrome c is large, the geometry of the site appears quite constrained, as indicated by a spectral line shape showing a single species. Intersystem crossing occurred predominantly to the T2 > zero-field spin sublevel. EPR line shape changes with respect to temperature of Zn cyt c are interpreted in terms of vibronic coupling, and a maximum Jahn-Teller crystal-field splitting of approximately 180 cm-1 is obtained. Sn cytochrome c in comparison with the Zn protein exhibits a photoactivated triplet line shape that is less well resolved in the X-Y region. The magnitude of E value is approximately 60 x 10(-4) cm-1 at 4 K; its value rapidly tends toward zero with increasing temperature, from which a value for the Jahn-Teller crystal-field splitting of > or = 40 cm-1 is estimated. In contrast to those for the metal cytochromes, the magnitude of E value for the free-base derivative was essentially zero at all temperatures studied. This finding is discussed as a consequence of an excited-state tautomerization process that occurs even at 4 K.
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Affiliation(s)
- P J Angiolillo
- Johnson Research Foundation, Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia 19104, USA
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Abstract
The developments in the field of biological electron transfer over the past 2 years are reviewed. Attention is given to theoretical developments, especially with respect to the concept of 'electronic pathways' inside proteins, and the association process of redox proteins in solution and the idea of 'conformational gating'.
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Affiliation(s)
- G W Canters
- Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, The Netherlands
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21
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Abstract
Plastocyanin is one of the best characterized of the photosynthetic electron transfer proteins. Since the determination of the structure of poplar plastocyanin in 1978, the structure of algal (Scenedesmus, Enteromorpha, Chlamydomonas) and plant (French bean) plastocyanins has been determined either by crystallographic or NMR methods, and the poplar structure has been refined to 1.33 A resolution. Despite the sequence divergence among plastocyanins of algae and vascular plants (e.g., 62% sequence identity between the Chlamydomonas and poplar proteins), the three-dimensional structures are remarkably conserved (e.g., 0.76 A rms deviation in the C alpha positions between the Chlamydomonas and poplar proteins). Structural features include a distorted tetrahedral copper binding site at one end of an eight-stranded antiparallel beta-barrel, a pronounced negative patch, and a flat hydrophobic surface. The copper site is optimized for its electron transfer function, and the negative and hydrophobic patches are proposed to be involved in recognition of physiological reaction partners. Chemical modification, cross-linking, and site-directed mutagenesis experiments have confirmed the importance of the negative and hydrophobic patches in binding interactions with cytochrome f and Photosystem I, and validated the model of two functionally significant electron transfer paths in plastocyanin. One putative electron transfer path is relatively short (approximately 4 A) and involves the solvent-exposed copper ligand His-87 in the hydrophobic patch, while the other is more lengthy (approximately 12-15 A) and involves the nearly conserved residue Tyr-83 in the negative patch.
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Affiliation(s)
- M R Redinbo
- Department of Chemistry and Biochemistry and Molecular Biology Institute, University of California, Los Angeles 90024
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Meyer TE, Tollin G, Cusanovich MA. Protein interaction sites obtained via sequence homology. The site of complexation of electron transfer partners of cytochrome c revealed by mapping amino acid substitutions onto three-dimensional protein surfaces. Biochimie 1994; 76:480-8. [PMID: 7880887 DOI: 10.1016/0300-9084(94)90172-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Amino acid substitutions in all but the most divergent of cytochromes c have been categorized as being conservative or radical and mapped onto the three-dimensional structure of yeast cytochrome c. Color-coded, space-filling representations reveal a large 24 A diameter surface area which is invariant or conservatively substituted on the front left face of the cytochrome c molecule. Chemical modifications and mutations which inhibit complex formation and electron transfer with reaction partners also map to this surface. In sharp contrast, the back side of the protein is randomly substituted with both conservative and radical replacements. The invariant/conservatively substituted surface on the front of cytochrome c thus defines the site of interaction with redox partners and provides a measure of its dimensions. Further, this analysis strongly suggests that there is only a single site of oxidation and reduction on cytochrome c for all of its physiological reactions. The same analysis applied to bacterial cytochrome c2 shows that its conserved surface is similar in size and location to that of cytochrome c. Analyses of native and model reaction partners of cytochromes c and c2, such as cytochrome b5, plastocyanin, and bacterial photosynthetic reaction centers, also reveal probable active site surfaces for complexation and electron transfer, which are complementary in size to that of the c-type cytochromes. The availability of a three-dimensional structure and of several closely related amino acid sequences for a given functional class of protein is the only limitation on this type of analysis, which can then serve as a basis for designing site-directed mutagenesis experiments.
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Affiliation(s)
- T E Meyer
- Department of Biochemistry, University of Arizona, Tucson 85721
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Qin L, Kostić NM. Importance of protein rearrangement in the electron-transfer reaction between the physiological partners cytochrome f and plastocyanin. Biochemistry 1993; 32:6073-80. [PMID: 8507642 DOI: 10.1021/bi00074a019] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Cytochrome f from turnip and plastocyanin from French bean were noninvasively cross-linked in the presence of the carbodiimide EDC so that the exposed heme edge in the former protein abuts the acidic patch remote from the copper site in the latter [Morand, L.Z., Frame, M.K., Colvert, K.K., Johnson, D.A., Krogmann, D.W., & Davis, D.J. (1989) Biochemistry 28, 8039]. The molecular mass, reduction potentials, and UV-visible and ESR spectra of the covalent complex were consistent with the composition cyt/pc and with a lack of noticeable structural perturbations of the protein molecules. Isoelectric focusing showed the presence of N-acylurea groups, byproducts of the cross-linking reaction [Zhou, J.S., Brothers, H.M. II, Neddersen, J.P., Peerey, L.M., Cotton, T.M., & Kostić, N.M. (1992) Bioconjugate Chem. 3, 382]. Laser flash spectroscopy, with riboflavin semiquinone as the reductant, showed that the electrontransfer reaction within the covalent complex cyt(II)/pc(II) is either undetectably slow or reversible. The question was resolved by monitoring, during redox titrations, the 1H NMR line widths of the heme methyl groups in free ferricytochrome f and in this protein cross-linked to plastocyanin.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- L Qin
- Department of Chemistry, Iowa State University, Ames 50011
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