1
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Wilson LA, Melville JN, Pedroso MM, Krco S, Hoelzle R, Zaugg J, Southam G, Virdis B, Evans P, Supper J, Harmer JR, Tyson G, Clark A, Schenk G, Bernhardt PV. Kinetic, electrochemical and spectral characterization of bacterial and archaeal rusticyanins; unexpected stability issues and consequences for applications in biotechnology. J Inorg Biochem 2024; 256:112539. [PMID: 38593609 DOI: 10.1016/j.jinorgbio.2024.112539] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Revised: 03/21/2024] [Accepted: 03/21/2024] [Indexed: 04/11/2024]
Abstract
Motivated by the ambition to establish an enzyme-driven bioleaching pathway for copper extraction, properties of the Type-1 copper protein rusticyanin from Acidithiobacillus ferrooxidans (AfR) were compared with those from an ancestral form of this enzyme (N0) and an archaeal enzyme identified in Ferroplasma acidiphilum (FaR). While both N0 and FaR show redox potentials similar to that of AfR their electron transport rates were significantly slower. The lack of a correlation between the redox potentials and electron transfer rates indicates that AfR and its associated electron transfer chain evolved to specifically facilitate the efficient conversion of the energy of iron oxidation to ATP formation. In F. acidiphilum this pathway is not as efficient unless it is up-regulated by an as of yet unknown mechanism. In addition, while the electrochemical properties of AfR were consistent with previous data, previously unreported behavior was found leading to a form that is associated with a partially unfolded form of the protein. The cyclic voltammetry (CV) response of AfR immobilized onto an electrode showed limited stability, which may be connected to the presence of the partially unfolded state of this protein. Insights gained in this study may thus inform the engineering of optimized rusticyanin variants for bioleaching processes as well as enzyme-catalyzed solubilization of copper-containing ores such as chalcopyrite.
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Affiliation(s)
- Liam A Wilson
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Jamie N Melville
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Marcelo M Pedroso
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Stefan Krco
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Robert Hoelzle
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia; Australian Centre for Ecogenomics, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Julian Zaugg
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia; Australian Centre for Ecogenomics, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Gordon Southam
- School of the Environment, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Bernardino Virdis
- Australian Centre for Water and Environmental Biotechnology, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Paul Evans
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia; Australian Centre for Ecogenomics, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Jenna Supper
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia; Australian Centre for Ecogenomics, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Jeffrey R Harmer
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Gene Tyson
- Centre for Microbiome Research, Queensland University of Technology, Woolloongabba, QLD 4102, Australia
| | - Alice Clark
- Sustainable Minerals Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Gerhard Schenk
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia; Australian Centre for Ecogenomics, The University of Queensland, Brisbane, QLD 4072, Australia; Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD 4072, Australia; Sustainable Minerals Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
| | - Paul V Bernhardt
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
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2
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Khorsand FR, Aziziyan F, Khajeh K. Factors influencing amyloid fibril formation. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2024; 206:55-83. [PMID: 38811089 DOI: 10.1016/bs.pmbts.2024.03.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2024]
Abstract
Protein aggregation is a complex process with several stages that lead to the formation of complex structures and shapes with a broad variability in stability and toxicity. The aggregation process is affected by various factors and environmental conditions that disrupt the protein's original state, including internal factors like mutations, expression levels, and polypeptide chain truncation, as well as external factors, such as dense molecular surroundings, post-translation modifications, and interactions with other proteins, nucleic acids, small molecules, metal ions, chaperones, and lipid membranes. During the aggregation process, the biological activity of an aggregating protein may be reduced or eliminated, whereas the resulting aggregates may have the potential to be immunogenic, or they may have other undesirable properties. Finding the cause(s) of protein aggregation and controlling it to an acceptable level is among the most crucial topics of research in academia and biopharmaceutical companies. This chapter aims to review intrinsic pathways of protein aggregation and potential extrinsic variables that influence this process.
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Affiliation(s)
| | - Fatemeh Aziziyan
- Department of Biochemistry, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran
| | - Khosro Khajeh
- Department of Biochemistry, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran.
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3
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Tang B, Chong K, Massefski W, Evans R. Quantitative Interpretation of Protein Diffusion Coefficients in Mixed Protiated-Deuteriated Aqueous Solvents. J Phys Chem B 2022; 126:5887-5895. [PMID: 35917500 PMCID: PMC9376945 DOI: 10.1021/acs.jpcb.2c03554] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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Diffusion-ordered nuclear magnetic resonance (NMR) spectroscopy
is widely used for the analysis of mixtures, dispersing the signals
of different species in a two-dimensional spectrum according to their
diffusion coefficients. However, interpretation of these diffusion
coefficients is typically purely qualitative, for example, to deduce
which species are bigger or smaller. In studies of proteins in solution,
important questions concern the molecular weight of the proteins,
the presence or absence of aggregation, and the degree of folding.
The Stokes–Einstein Gierer–Wirtz estimation (SEGWE)
method has been previously developed to simplify the complex relationship
between diffusion coefficient and molecular mass, allowing the prediction
of a species’ diffusion coefficient in a pure solvent based
on its molecular weight. Here, we show that SEGWE can be extended
to successfully predict both peptide and protein diffusion coefficients
in mixed protiated–deuteriated water samples and, hence, distinguish
effectively between globular and disordered proteins.
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Affiliation(s)
- Bridget Tang
- Aston Institute of Materials Research, Aston University, Birmingham B4 7ET, U.K
| | - Katie Chong
- Energy and Bioproducts Research Institute (EBRI), Aston University, Birmingham B4 7ET, U.K
| | - Walter Massefski
- Department of Chemistry Instrumentation Facility, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Robert Evans
- Aston Institute of Materials Research, Aston University, Birmingham B4 7ET, U.K
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4
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Zhan Y, Yang M, Zhang S, Zhao D, Duan J, Wang W, Yan L. Iron and sulfur oxidation pathways of Acidithiobacillus ferrooxidans. World J Microbiol Biotechnol 2019; 35:60. [PMID: 30919119 DOI: 10.1007/s11274-019-2632-y] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Accepted: 03/08/2019] [Indexed: 12/13/2022]
Abstract
Acidithiobacillus ferrooxidans is a gram-negative, autotrophic and rod-shaped bacterium. It can gain energy through the oxidation of Fe(II) and reduced inorganic sulfur compounds for bacterial growth when oxygen is sufficient. It can be used for bio-leaching and bio-oxidation and contributes to the geobiochemical circulation of metal elements and nutrients in acid mine drainage environments. The iron and sulfur oxidation pathways of A. ferrooxidans play key roles in bacterial growth and survival under extreme circumstances. Here, the electrons transported through the thermodynamically favourable pathway for the reduction to H2O (downhill pathway) and against the redox potential gradient reduce to NAD(P)(H) (uphill pathway) during the oxidation of Fe(II) were reviewed, mainly including the electron transport carrier, relevant operon and regulation of its expression. Similar to the electron transfer pathway, the sulfur oxidation pathway of A. ferrooxidans, related genes and operons, sulfur oxidation mechanism and sulfur oxidase system are systematically discussed.
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Affiliation(s)
- Yue Zhan
- Heilongjiang Provincial Key Laboratory of Environmental Microbiology and Recycling of Argo-Waste in Cold Region, College of Life Science and Biotechnology, Heilongjiang Bayi Agricultural University, 5 Xinfeng Road, Daqing, 163319, Heilongjiang Province, People's Republic of China
| | - Mengran Yang
- Heilongjiang Provincial Key Laboratory of Environmental Microbiology and Recycling of Argo-Waste in Cold Region, College of Life Science and Biotechnology, Heilongjiang Bayi Agricultural University, 5 Xinfeng Road, Daqing, 163319, Heilongjiang Province, People's Republic of China
| | - Shuang Zhang
- Heilongjiang Provincial Key Laboratory of Environmental Microbiology and Recycling of Argo-Waste in Cold Region, College of Life Science and Biotechnology, Heilongjiang Bayi Agricultural University, 5 Xinfeng Road, Daqing, 163319, Heilongjiang Province, People's Republic of China
| | - Dan Zhao
- Heilongjiang Provincial Key Laboratory of Environmental Microbiology and Recycling of Argo-Waste in Cold Region, College of Life Science and Biotechnology, Heilongjiang Bayi Agricultural University, 5 Xinfeng Road, Daqing, 163319, Heilongjiang Province, People's Republic of China
| | - Jiangong Duan
- School of Pharmacy, Lanzhou University, Donggang West Road No. 199, Lanzhou, 730020, Gansu Province, People's Republic of China
| | - Weidong Wang
- Heilongjiang Provincial Key Laboratory of Environmental Microbiology and Recycling of Argo-Waste in Cold Region, College of Life Science and Biotechnology, Heilongjiang Bayi Agricultural University, 5 Xinfeng Road, Daqing, 163319, Heilongjiang Province, People's Republic of China
| | - Lei Yan
- Heilongjiang Provincial Key Laboratory of Environmental Microbiology and Recycling of Argo-Waste in Cold Region, College of Life Science and Biotechnology, Heilongjiang Bayi Agricultural University, 5 Xinfeng Road, Daqing, 163319, Heilongjiang Province, People's Republic of China. .,College of Food Science, Heilongjiang Bayi Agricultural University, 5 Xinfeng Road, Daqing, 163319, Heilongjiang Province, People's Republic of China.
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5
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Unfolding pathway of CotA-laccase and the role of copper on the prevention of refolding through aggregation of the unfolded state. Biochem Biophys Res Commun 2012; 422:442-6. [DOI: 10.1016/j.bbrc.2012.05.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Accepted: 05/02/2012] [Indexed: 11/29/2022]
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6
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Folding and unfolding in the blue copper protein rusticyanin: role of the oxidation state. Bioinorg Chem Appl 2011:54232. [PMID: 18354738 PMCID: PMC2267886 DOI: 10.1155/2007/54232] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2007] [Revised: 05/02/2007] [Accepted: 06/27/2007] [Indexed: 11/17/2022] Open
Abstract
The unfolding process of the blue copper protein rusticyanin has been studied from the structural and the thermodynamic points of view at two pH values (pH 2.5 and 7.0). When Rc unfolds, copper ion remains bound to the polypeptide chain. Nuclear magnetic resonance data suggest that three of the copper ligands in the folded state are bound to the metal ion in the unfolded form, while the other native ligand is detached. These structural changes are reflected in the redox potentials of the protein in both folded and unfolded forms. The affinities of the copper ion in both redox states have been also determined at the two specified pH values. The results indicate that the presence of two histidine ligands in the folded protein can compensate the change in the net charge that the copper ion receives from their ligands, while, in the unfolded protein, charges of aminoacids are completely transferred to the copper ion, altering decisively the relative stability of its two-redox states.
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7
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Chaboy J, Díaz-Moreno S, Díaz-Moreno I, De la Rosa MA, Díaz-Quintana A. How the local geometry of the Cu-binding site determines the thermal stability of blue copper proteins. ACTA ACUST UNITED AC 2011; 18:25-31. [PMID: 21276936 DOI: 10.1016/j.chembiol.2010.12.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2010] [Revised: 12/09/2010] [Accepted: 12/10/2010] [Indexed: 12/16/2022]
Abstract
Identifying the factors that govern the thermal resistance of cupredoxins is essential for understanding their folding and stability, and for improving our ability to design highly stable enzymes with potential biotechnological applications. Here, we show that the thermal unfolding of plastocyanins from two cyanobacteria--the mesophilic Synechocystis and the thermophilic Phormidium--is closely related to the short-range structure around the copper center. Cu K-edge X-ray absorption spectroscopy shows that the bond length between Cu and the S atom from the cysteine ligand is a key structural factor that correlates with the thermal stability of the cupredoxins in both oxidized and reduced states. These findings were confirmed by an additional study of a site-directed mutant of Phormidium plastocyanin showing a reverse effect of the redox state on the thermal stability of the protein.
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Affiliation(s)
- Jesús Chaboy
- Instituto de Ciencia de Materiales de Aragón, Consejo Superior de Investigaciones Científicas-Universidad de Zaragoza, 50009 Zaragoza, Spain.
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8
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Muñoz-López FJ, Beltrán EF, Díaz-Moreno S, Díaz-Moreno I, Subías G, De la Rosa MA, Díaz-Quintana A. Modulation of copper site properties by remote residues determines the stability of plastocyanins. FEBS Lett 2010; 584:2346-50. [PMID: 20398655 DOI: 10.1016/j.febslet.2010.04.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Revised: 04/07/2010] [Accepted: 04/07/2010] [Indexed: 11/18/2022]
Abstract
The metal cofactor determines the thermal stability in cupredoxins, but how the redox state of copper modulates their melting points remains unknown. The metal coordination environment is highly conserved in cyanobacterial plastocyanins. However, the oxidised form is more stable than the reduced one in thermophilic Phormidium, but the opposite occurs in mesophilic Synechocystis. We have performed neutral amino-acid substitutions at loops of Phormidium plastocyanin far from the copper site. Notably, mutation P49G/G50P confers a redox-dependent thermal stability similar to that of the mesophilic plastocyanin. Moreover, X-ray absorption spectroscopy reveals that P49G/G50P mutation makes the electron density distribution at the oxidised copper site shift towards that of Synechocystis plastocyanin.
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Affiliation(s)
- Francisco J Muñoz-López
- Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla y CSIC, Sevilla, Spain
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9
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Kapoor D, Singh B, Subramanian K, Guptasarma P. Creation of a new eye lens crystallin (Gambeta) through structure-guided mutagenic grafting of the surface of betaB2 crystallin onto the hydrophobic core of gammaB crystallin. FEBS J 2009; 276:3341-53. [PMID: 19438717 DOI: 10.1111/j.1742-4658.2009.07059.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The degree of conservation of three-dimensional folds in protein superfamilies is greater than that of amino acid sequences. Therefore, very different groups of residues (and schemes of residue packing) can be found displayed upon similar structural scaffolds. We have previously demonstrated the workability of a protein engineering-based method for rational mixing of the interior features of an all-beta enzyme with the substrate-binding and catalytic (surface) features of another enzyme whose sequence is not similar but which is structurally homologous to the first enzyme. Here, we extend this method to whole-protein surfaces and interiors. We show how two all-beta Greek key proteins, betaB2 crystallin and gammaB crystallin, can be recombined to produce a new protein through rational transplantation of the entire surface of betaB2 crystallin upon the structure of gammaB crystallin, without altering the latter's interior. This new protein, Gambeta, consists of 61 residues possessing the same identity at structurally equivalent positions in betaB2- and gammaB crystallin, 91 surface residues unique to betaB2 crystallin, and 27 interior residues unique to gammaB crystallin. Gambeta displays a mixture of the structural/biochemical characteristics, surface features and colligative properties of its progenitor crystallins. It also displays optical properties common to both progenitor crystallins (i.e. retention of transparency at high concentrations, as well as high refractivity). The folding of a protein with such a 'patchwork' residue ancestry suggests that interior/surface transplants involving all-beta proteins are a feasible engineering strategy.
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Affiliation(s)
- Divya Kapoor
- Division of Protein Science & Engineering, Institute of Microbial Technology, Chandigarh 160036, Council of Scientific & Industrial Research, New Delhi, India
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10
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Fernandes AT, Martins LO, Melo EP. The hyperthermophilic nature of the metallo-oxidase from Aquifex aeolicus. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2008; 1794:75-83. [PMID: 18930169 DOI: 10.1016/j.bbapap.2008.09.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2008] [Revised: 08/22/2008] [Accepted: 09/11/2008] [Indexed: 10/21/2022]
Abstract
The stability of the Aquifex aeolicus multicopper oxidase (McoA) was studied by spectroscopy, calorimetry and chromatography to understand its thermophilic nature. The enzyme is hyperthermostable as deconvolution of the differential scanning calorimetry trace shows that thermal unfolding is characterized by temperature values at the mid-point of 105, 110 and 114 degrees C. Chemical denaturation revealed however a very low stability at room temperature (2.8 kcal/mol) because copper bleaching/depletion occur before the unfolding of the tertiary structure and McoA is highly prone to aggregate. Indeed, unfolding kinetics measured with the stopped-flow technique quantified the stabilizing effect of copper on McoA (1.5 kcal/mol) and revealed quite an uncommon observation further confirmed by light scattering and gel filtration chromatography: McoA aggregates in the presence of guanidinium hydrochloride, i.e., under unfolding conditions. The aggregation process results from the accumulation of a quasi-native state of McoA that binds to ANS and is the main determinant of the stability curve of McoA. Kinetic partitioning between aggregation and unfolding leads to a very low heat capacity change and determines a flat dependence of stability on temperature.
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Affiliation(s)
- André T Fernandes
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2781-901 Oeiras, Portugal
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11
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Feio MJ, Díaz-Quintana A, Navarro JA, De la Rosa MA. Thermal unfolding of plastocyanin from the mesophilic cyanobacterium Synechocystis sp. PCC 6803 and comparison with its thermophilic counterpart from Phormidium laminosum. Biochemistry 2006; 45:4900-6. [PMID: 16605257 DOI: 10.1021/bi052312q] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The thermal unfolding of plastocyanin from the mesophilic cyanobacterium Synechocystis is described herein, and the results are compared with those obtained for the homologous thermophilic protein from Phormidium laminosum. The thermal unfolding is irreversible under all the conditions that were investigated. Plastocyanin from the thermophilic organism, both in the native state and in the apoprotein form, proved to be more thermostable than its mesophilic counterpart under all experimental conditions. Synechocystis reduced plastocyanin has been shown to be more stable than the oxidized species, both with respect to the required temperature for protein unfolding and with respect to the kinetics of the process. This behavior contrasts with that observed for Phormidium plastocyanin, in which the oxidized form is the more stable one. The unfolding pH dependence and kinetic studies indicate that around physiological pH, the most kinetically stable form is also the one more resistant to temperature variations, suggesting a close compromise between function and stability. Molecular dynamics simulations suggest that Phormidium and Synechocystis plastocyanins follow different unfolding pathways that affect different protein areas and which could be responsible for the observed dissimilar thermal resistance.
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Affiliation(s)
- Maria J Feio
- Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla y Consejo Superior de Investigaciones Científicas, Centro de Investigaciones Científicas Isla de la Cartuja, Sevilla, Spain
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12
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Alcaraz LA, Donaire A. Rapid binding of copper(I) to folded aporusticyanin. FEBS Lett 2005; 579:5223-6. [PMID: 16165132 DOI: 10.1016/j.febslet.2005.08.048] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2005] [Revised: 08/19/2005] [Accepted: 08/19/2005] [Indexed: 11/17/2022]
Abstract
Kinetics of copper uptake in both oxidation states by the folded and unfolded forms of the type 1 copper protein rusticyanin have been studied. The speed of the binding of copper(I) to the folded rusticyanin is fast, and of the same order of magnitude as copper(I) uptake by the unfolded form. Thus, the binding of copper can be subsequent to the protein folding, contrary to previous proposals. Implications for the mechanism of the formation of the active holoprotein in vivo are discussed.
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Affiliation(s)
- Luis A Alcaraz
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández de Elche, Edificio Torregaitán, Avda. de la Universidad, s/n, 03202 Elche Alicante, Spain
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13
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Alcaraz LA, Jiménez B, Moratal JM, Donaire A. An NMR view of the unfolding process of rusticyanin: Structural elements that maintain the architecture of a beta-barrel metalloprotein. Protein Sci 2005; 14:1710-22. [PMID: 15987900 PMCID: PMC2253362 DOI: 10.1110/ps.051337505] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The unfolding process of the blue copper protein rusticyanin (Rc) as well as its dynamic and D(2)O/H(2)O exchange properties in an incipient unfolded state have been studied by heteronuclear NMR spectroscopy. Titrations of apo, Cu(I), and Cu(II)Rc with guanidinium chloride (GdmCl) show that the copper ion stabilizes the folded species and remains bound in the completely unfolded state. The oxidized state of the copper ion is more efficient than the reduced form in this respect. The long loop of Rc (where the first ligand of the copper ion is located) is one of the most mobile domains of the protein. This region has no defined secondary structure elements and is prone to exchange its amide protons. In contrast, the last loop (including a short alpha-helix) and the last beta-strand (where the other three ligands of the metal ion are located) form the most rigid domain of the protein. The results taken as a whole suggest that the first ligand detaches from the metal ion when the protein unfolds, while the other three ligands remain bound to it. The implications of these findings for the biological folding process of Rc are also discussed.
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Affiliation(s)
- Luis A Alcaraz
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Edificio Torregaitán, Elche (Alicante), Spain
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