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Galano-Frutos JJ, Nerín-Fonz F, Sancho J. Calculation of Protein Folding Thermodynamics Using Molecular Dynamics Simulations. J Chem Inf Model 2023; 63:7791-7806. [PMID: 37955428 PMCID: PMC10751793 DOI: 10.1021/acs.jcim.3c01107] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 10/18/2023] [Accepted: 10/18/2023] [Indexed: 11/14/2023]
Abstract
Despite advances in artificial intelligence methods, protein folding remains in many ways an enigma to be solved. Accurate computation of protein folding energetics could help drive fields such as protein and drug design and genetic interpretation. However, the challenge of calculating the state functions governing protein folding from first-principles remains unaddressed. We present here a simple approach that allows us to accurately calculate the energetics of protein folding. It is based on computing the energy of the folded and unfolded states at different temperatures using molecular dynamics simulations. From this, two essential quantities (ΔH and ΔCp) are obtained and used to calculate the conformational stability of the protein (ΔG). With this approach, we have successfully calculated the energetics of two- and three-state proteins, representatives of the major structural classes, as well as small stability differences (ΔΔG) due to changes in solution conditions or variations in an amino acid residue.
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Affiliation(s)
- Juan J. Galano-Frutos
- Department
of Biochemistry, Molecular and Cell Biology, Faculty of Science, University of Zaragoza, 50009 Zaragoza, Spain
- Biocomputation
and Complex Systems Physics Institute (BIFI), Joint Unit GBs-CSIC, University of Zaragoza, 50018 Zaragoza, Spain
| | - Francho Nerín-Fonz
- Department
of Biochemistry, Molecular and Cell Biology, Faculty of Science, University of Zaragoza, 50009 Zaragoza, Spain
| | - Javier Sancho
- Department
of Biochemistry, Molecular and Cell Biology, Faculty of Science, University of Zaragoza, 50009 Zaragoza, Spain
- Biocomputation
and Complex Systems Physics Institute (BIFI), Joint Unit GBs-CSIC, University of Zaragoza, 50018 Zaragoza, Spain
- Aragon
Health Research Institute (IIS Aragón), 50009 Zaragoza, Spain
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2
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Patel AY, Jonnalagadda KS, Paradis N, Vaden TD, Wu C, Caputo GA. Effects of Ionic Liquids on Metalloproteins. Molecules 2021; 26:514. [PMID: 33478102 PMCID: PMC7835893 DOI: 10.3390/molecules26020514] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Revised: 01/04/2021] [Accepted: 01/08/2021] [Indexed: 01/28/2023] Open
Abstract
In the past decade, innovative protein therapies and bio-similar industries have grown rapidly. Additionally, ionic liquids (ILs) have been an area of great interest and rapid development in industrial processes over a similar timeline. Therefore, there is a pressing need to understand the structure and function of proteins in novel environments with ILs. Understanding the short-term and long-term stability of protein molecules in IL formulations will be key to using ILs for protein technologies. Similarly, ILs have been investigated as part of therapeutic delivery systems and implicated in numerous studies in which ILs impact the activity and/or stability of protein molecules. Notably, many of the proteins used in industrial applications are involved in redox chemistry, and thus often contain metal ions or metal-associated cofactors. In this review article, we focus on the current understanding of protein structure-function relationship in the presence of ILs, specifically focusing on the effect of ILs on metal containing proteins.
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Affiliation(s)
- Aashka Y. Patel
- Department of Chemistry and Biochemistry, Rowan University, Glassboro, NJ 08028, USA; (A.Y.P.); (N.P.); (T.D.V.); (C.W.)
| | | | - Nicholas Paradis
- Department of Chemistry and Biochemistry, Rowan University, Glassboro, NJ 08028, USA; (A.Y.P.); (N.P.); (T.D.V.); (C.W.)
| | - Timothy D. Vaden
- Department of Chemistry and Biochemistry, Rowan University, Glassboro, NJ 08028, USA; (A.Y.P.); (N.P.); (T.D.V.); (C.W.)
| | - Chun Wu
- Department of Chemistry and Biochemistry, Rowan University, Glassboro, NJ 08028, USA; (A.Y.P.); (N.P.); (T.D.V.); (C.W.)
- Department of Molecular and Cellular Biosciences, Rowan University, Glassboro, NJ 08028, USA
| | - Gregory A. Caputo
- Department of Chemistry and Biochemistry, Rowan University, Glassboro, NJ 08028, USA; (A.Y.P.); (N.P.); (T.D.V.); (C.W.)
- Department of Molecular and Cellular Biosciences, Rowan University, Glassboro, NJ 08028, USA
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3
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Galano-Frutos JJ, Sancho J. Accurate Calculation of Barnase and SNase Folding Energetics Using Short Molecular Dynamics Simulations and an Atomistic Model of the Unfolded Ensemble: Evaluation of Force Fields and Water Models. J Chem Inf Model 2019; 59:4350-4360. [PMID: 31513394 DOI: 10.1021/acs.jcim.9b00430] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
As proteins perform most cellular functions, quantitative understanding of protein energetics is required to gain control of biological phenomena. Accurate models of native proteins can be obtained experimentally, but the lack of equally fine models of unfolded ensembles impedes the calculation of protein folding energetics from first principles. Here, we show that an atomistic unfolded ensemble model, consisting of a few dozen conformations built from a protein sequence, can be used in conjunction with an X-ray structure of its native state to calculate accurately by difference the changes in enthalpy and heat capacity of the polypeptide upon folding. The calculation is done using molecular dynamics simulations, popular force fields, and water models, and for the two model proteins studied (barnase and SNase), the results agree within error or are very close to their experimentally determined properties. The enthalpy sampling of the unfolded ensemble is done through short 2 ns simulations that do not significantly modify the representative distribution of Rg of the starting conformations. The impressive accuracy obtained opens the possibility to investigate quantitatively systems or phenomena not amenable to experiment and paves the way for addressing the calculation of protein conformational stability (i.e., the change in Gibbs energy upon folding), a central goal of structural biology. So far, these calculated enthalpy and heat capacity changes, combined with the experimentally determined melting temperatures of the corresponding protein, allow us to reproduce the stability curves of both barnase and SNase.
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Affiliation(s)
- Juan José Galano-Frutos
- Department of Biochemistry and Molecular and Cellular Biology , University of Zaragoza , Pedro Cerbuna 12 , Zaragoza 50009 , Spain.,Biocomputation and Complex Systems Physics Institute (Joint Units: BIFI-IQFR (CSIC) and GBsC-CSIC) , University of Zaragoza , Mariano Esquillor s/n, Edificio I + D , Zaragoza 50018 , Spain
| | - Javier Sancho
- Department of Biochemistry and Molecular and Cellular Biology , University of Zaragoza , Pedro Cerbuna 12 , Zaragoza 50009 , Spain.,Biocomputation and Complex Systems Physics Institute (Joint Units: BIFI-IQFR (CSIC) and GBsC-CSIC) , University of Zaragoza , Mariano Esquillor s/n, Edificio I + D , Zaragoza 50018 , Spain.,Aragon Health Research Institute (IIS Aragón) , Avda. San Juan Bosco 13 , Zaragoza 50009 , Spain
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4
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Sankaranarayanan K, Dhathathreyan A, Krägel J, Miller R. Interfacial viscoelasticity of myoglobin at air/water and air/solution interfaces: role of folding and clustering. J Phys Chem B 2012; 116:895-902. [PMID: 22176527 DOI: 10.1021/jp2100733] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
This study describes the folding and organization of myoglobin (Mb) at the solution/air interface at different pH values of 2.5, 3.5, 5.5, 7.5, and 8.5. Dynamic surface tension and the associated dilational and shear viscoelasticity for Mb at these pH's have been studied using a sinusoidal surface compression and expansion for frequencies ranging from 0.01 to 0.4 Hz. The changes in dilational viscosity, elasticity, and fluorescence lifetime measurements have been related to the conformational changes of the protein films at the interface. It is observed that while acid-induced denaturation of the protein does not lead to large changes in dilational properties, the shear properties on the other hand are strongly influenced by it, and the protein behaves like a shear-thickening fluid. At higher pH, particularly at the isoelectric point, Mb is pseudoplastic indicating an increase in the shear viscosity. These results are strongly suggestive of formation of hydrophobic clusters at the protein-buffer interface because of the change in the overall charge distributions.
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5
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Norberto DR, Vieira JM, de Souza AR, Bispo JAC, Bonafe CFS. Pressure- and Urea-Induced Denaturation of Bovine Serum Albumin: Considerations about Protein Heterogeneity. ACTA ACUST UNITED AC 2012. [DOI: 10.4236/ojbiphy.2012.21002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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6
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Abstract
Following isolation and purification, it is often necessary to store proteins and peptides for extended periods of time before performing detailed biophysical, enzymatic, and structural proteomics. Therefore, it is essential that the pure target protein maintain its original biological (or functional) behavior over an extended period of storage which may range from weeks to years. Protein pharmaceuticals must remain viable following extensive shipping and storage, and they must remain devoid of all possible inactivation processes. The shelf life of a protein depends on both the intrinsic nature of the protein and the storage conditions. Proteins (especially enzymes) must be stored at an appropriate temperature and pH range and frequently in the presence of concentrated (approximately 1 M) glycerol, sucrose, or a similar substance, for the proteins to retain activity and prevent aggregation. This article discusses the major causes of protein inactivation and describes a range of measures that can be adopted to maintain the stability and solubility of proteins.
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7
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Talla-Singh D, Stites WE. Refinement of noncalorimetric determination of the change in heat capacity, DeltaC(p), of protein unfolding and validation across a wide temperature range. Proteins 2008; 71:1607-16. [PMID: 18384147 DOI: 10.1002/prot.22016] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The change in heat capacity, DeltaC(p), on protein unfolding has been usually determined by calorimetry. A noncalorimetric method which employs the Gibbs-Helmholtz relationship to determine DeltaC(p) has seen some use. Generally, in this method the free energy change on unfolding of the protein is determined at a variety of temperatures and the temperature at which DeltaG is zero, T(m), and change in enthalpy at T(m) are determined by thermal denaturation and DeltaC(p) is then calculated using the Gibbs-Helmholtz equation. We show here that an abbreviated method with stability determinations at just two temperatures gives values of DeltaC(p) consistent with values from free energy change on unfolding determination at a much wider range of temperatures. Further, even the free energy change on unfolding from a single solvent denaturation at the proper temperature, when coupled with the melting temperature, T(m), and the van't Hoff enthalpy, DeltaH(vH), from a thermal denaturation, gives a reasonable estimate of DeltaC(p), albeit with greater uncertainty than solvent denaturations at two temperatures. We also find that nonlinear regression of the Gibbs-Helmholtz equation as a function of stability and temperature while simultaneously fitting DeltaC(p), T(m), and DeltaH(vH) gives values for the last two parameters that are in excellent agreement with experimental values.
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Affiliation(s)
- Deepika Talla-Singh
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701-1201, USA
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8
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Byrne MP, Stites WE. Thermal denaturations of staphylococcal nuclease wild-type and mutants monitored by fluorescence and circular dichroism are similar: lack of evidence for other than a two state thermal denaturation. Biophys Chem 2007; 125:490-6. [PMID: 17134819 PMCID: PMC1941688 DOI: 10.1016/j.bpc.2006.10.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2006] [Revised: 10/28/2006] [Accepted: 10/29/2006] [Indexed: 11/18/2022]
Abstract
It is unclear whether the thermal denaturation of staphylococcal nuclease is a two state, three state, or variable two state process. The thermal denaturation of wild-type staphylococcal nuclease was followed by tryptophan fluorescence and circular dichroism signal at 222 nm, forty-two and fourteen times, respectively. Analysis of this data using a simple two state model gave melting temperatures of 53.0+/-0.4 degrees C (fluorescence) and 52.7+/-0.6 degrees C (CD) and van't Hoff enthalpies of 82.4+/-2.6 kcal/mol and 88.6+/-4.2 kcal/mol. Ninety-seven mutants also had these parameters determined by both fluorescence and CD. The average difference between the melting temperatures was 1.05+/-0.75 degrees and the average difference between van't Hoff enthalpies was 1.6+/-4.8 kcal/mol. These very similar results for the two spectroscopic probes of structure are discussed in the context of the different models that have been proposed for nuclease denaturation. It is concluded, for most nuclease variants, that the errors introduced by a two state assumption are negligible and either virtually all helical structure is lost in any initial unfolding event or any intermediate must have low stability.
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Affiliation(s)
- Michael P Byrne
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701-1201, USA
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9
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Rashid F, Sharma S, Baig MA, Bano B. Molten globule state of human placental cystatin (HPC) at low pH conditions and the effects of trifluoroethanol (TFE) and methanol. Biochem Cell Biol 2006; 84:126-34. [PMID: 16609692 DOI: 10.1139/o05-171] [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: 11/22/2022] Open
Abstract
Acid-induced conformational changes were studied in human placental cystatin (HPC) in terms of circular dichroism (CD) spectroscopy, the binding of hydrophobic dye 1-anilinonapthalene-8-sulphonic acid (ANS), and intrinsic fluorescence measurements. Our results show the formation of an acid-induced molten globule state at pH 2.0, with significant secondary and tertiary interactions that resemble the native state, exposed hydrophobic regions and the effects of trifluoroethanol (TFE) and methanol in conversion of the acid-denatured state of HPC to the alcohol-induced state, which is characterized by increased helical content, disrupted tertiary structure, and the absence of hydrophobic clusters. Alcohol-induced formation of α-helical structures at pH 2.0 is evident from the increase in the ellipticity values at 222 nm, with native-like secondary structural features at 40% TFE. The increase in helical content was observed up to 80% TFE concentration. The ability of TFE (40%) to refold acid-denatured HPC to native-state conformation is also supported by intrinsic and ANS fluorescence measurements.Key words: human placental cystatin, molten globule, acid-induced state, trifluoroethanol, methanol, CD spectroscopy, ANS fluorescence, pH, protein folding.
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Affiliation(s)
- Fouzia Rashid
- Department of Biochemistry, Faculty of Life Sciences, Aligarh Muslim University, India
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10
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Fitch CA, Whitten ST, Hilser VJ, García-Moreno E B. Molecular mechanisms of pH-driven conformational transitions of proteins: Insights from continuum electrostatics calculations of acid unfolding. Proteins 2006; 63:113-26. [PMID: 16400648 DOI: 10.1002/prot.20797] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The acid unfolding of staphylococcal nuclease (SNase) is very cooperative (Whitten and García-Moreno, Biochemistry 2000;39:14292-14304). As many as seven hydrogen ions (H+) are bound preferentially by the acid-unfolded state relative to the native (N) state in the pH range 3.2-3.9. To investigate the mechanism of acid unfolding, structure-based pKa calculations were performed with a variety of continuum electrostatic methods. The calculations reproduced successfully the H+ binding properties of the N state between pH 5 and 9, but they systematically overestimated the number of H+ bound upon acid unfolding. The calculated pKa values of all carboxylic residues in the N state were more depressed than they should be. The discrepancy between the observed and the calculated H+ uptake upon acid unfolding was not improved by using high protein dielectric constants, structures relaxed with molecular dynamics, or other empirical modifications implemented previously by others to maximize agreement between measured and calculated pKa values. This suggests an important role for conformational fluctuations of the backbone as important determinants of pKa values of carboxylic groups. Because no global or subglobal conformational changes have been observed previously for SNase under acidic conditions above the acid-unfolding region, these fluctuations must be local. The acid unfolding of SNase does not seem to involve the disruption of the N state by accruement of intramolecular repulsive interactions, nor the protonation of key ion paired carboxylic residues. It is more consistent with modest contributions from many H+ binding groups, with an important role for local conformational fluctuations in the coupling between H+ binding and the global structural transition.
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Affiliation(s)
- Carolyn A Fitch
- Department of Biophysics, Johns Hopkins University, Baltimore, Maryland 21218, USA
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11
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Haq SK, Rasheedi S, Sharma P, Ahmad B, Khan RH. Influence of salts and alcohols on the conformation of partially folded intermediate of stem bromelain at low pH. Int J Biochem Cell Biol 2005; 37:361-74. [PMID: 15474981 DOI: 10.1016/j.biocel.2004.07.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2004] [Revised: 06/23/2004] [Accepted: 07/09/2004] [Indexed: 11/26/2022]
Abstract
The effect of salts and alcohols was examined on the partially folded intermediate (PFI) state of stem bromelain reported at low pH (Haq, Rasheedi, and Khan (2002) European Journal of Biochemistry 269, 47-52) by a combination of optical methods like circular dichroism, intrinsic fluorescence and ANS binding. ESI mass spectrometry was also performed to see the effect, if any, on the overall tertiary structure of the protein. Increase in ionic strength by the addition of salts resulted in folded structures somewhat different from the native enzyme. Salt-induced intermediates are characterized by increase in helical content and a significantly reduced exposure of hydrophobic clusters relative to the state at pH 2.0. The emission wavelength maximum of intrinsic fluorescence was shifted towards that of native enzyme. ESI-MS data show decreased accessibility of ionizable/protonation sites suggestive of a folded structure. On the other hand, alcohol-induced intermediates though exhibiting increased helical content are apparently largely unfolded as observed by ESI. Thermal denaturation of a representative intermediate, each from the group of salts and alcohols examined, was also performed to check their relative stabilities. While the alcohol-induced state showed a cooperative thermal transition, the salt-induced state shows non-cooperative thermal denaturation.
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Affiliation(s)
- Soghra Khatun Haq
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh 202002, India
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12
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Harries D, Parsegian VA. Gibbs adsorption isotherm combined with Monte Carlo sampling to see action of cosolutes on protein folding. Proteins 2004; 57:311-21. [PMID: 15340918 DOI: 10.1002/prot.20182] [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: 11/05/2022]
Abstract
Driven by conditions set by smaller solutes, proteins fold and unfold. Experimentally, these conditions are stated as intensive variables--pH and other chemical potentials--as though small solutes were infinite resources that come at an externally varied free energy cost. Computationally, the finite spaces of simulation allow only fixed numbers of these solutes. By combining the analytic Gibbs adsorption isotherm with the computational Monte Carlo sampling of polymer configurations, we have been able to overcome an inherent limitation of computer simulation. The idea is to compute analytically the free energy changes wrought by solutes on each particular configuration. Then numerical computation is needed only to sample the set of configurations as efficiently as when no bathing solute is present. For illustration, the procedure is applied to an idealized two-dimensional heteropolymer to yield lessons about the effect of cosolutes on protein stability.
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Affiliation(s)
- Daniel Harries
- Laboratory of Physical and Structural Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA.
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13
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Guzman-Casado M, Parody-Morreale A, Robic S, Marqusee S, Sanchez-Ruiz JM. Energetic evidence for formation of a pH-dependent hydrophobic cluster in the denatured state of Thermus thermophilus ribonuclease H. J Mol Biol 2003; 329:731-43. [PMID: 12787674 DOI: 10.1016/s0022-2836(03)00513-8] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
NMR studies on the denatured states of proteins indicate that residual structure often resides predominantly in hydrophobic clusters. Such hydrophobic cluster formation implies burial of apolar surface and, consequently, is expected to cause a decrease in heat capacity. We report here that, in the case of ribonuclease H from the thermophile Thermus thermophilus, a sharp decrease in denatured-state heat capacity occurs at about pH 3.8; this result points to the formation of hydrophobic clusters triggered by the protonation of several (about four) carboxylic acid groups, and indicates that the burial of apolar surface is favored by the less hydrophilic character of the uncharged forms of Asp and Glu side-chains. The process is not accompanied by large changes in optically active structure, but appears to be highly cooperative, as indicated by the sharpness of the pH-induced transition in the heat capacity. This acid-induced hydrophobic burial in denatured T.thermophilus ribonuclease H is clearly reflected in the pH dependence of the denaturation temperature (i.e. an abrupt change of slope at about pH 3.8 is seen in the plot of denaturation temperature versus pH), supporting a role for such denatured-state hydrophobic clusters in protein stability. The finding of cooperative protonation of several groups coupled to surface burial in denatured T.thermophilus ribonuclease H emphasizes the potential complexity of denatured-state electrostatics and advises caution when attempting to predict denatured-state properties on the basis of simple electrostatic models. Finally, our results suggest a higher propensity for hydrophobic cluster formation in the denatured state of T.thermophilus ribonuclease H as compared with that of its mesophilic counterpart from Escherichia coli.
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Affiliation(s)
- Mercedes Guzman-Casado
- Facultad de Ciencias, Departamento de Quimica Fisica, Universidad de Granada, 18071, Granada, Spain
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14
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Gupta P, Khan RH, Saleemuddin M. Trifluoroethanol-induced "molten globule" state in stem bromelain. Arch Biochem Biophys 2003; 413:199-206. [PMID: 12729617 DOI: 10.1016/s0003-9861(03)00126-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
2,2,2-Trifluoroethanol (TFE) denatures proteins but also stabilizes/induces alpha helical conformation in partially/completely unfolded proteins. As reported earlier from this laboratory, stem bromelain is known to exist as a partially folded intermediate (PFI) at pH 2.0. The effect of increasing concentration of TFE on the PFI of bromelain has been investigated by circular dichroism (CD), fluorescence emission spectroscopy, binding of the hydrophobic dye 1-anilino 8-naphthalene sulfonic acid (ANS), and near-UV CD temperature transition. Far-UV CD spectra show considerable accumulation of secondary structure at 70% (v/v) concentration of TFE with spectral features resembling the pH 7.0 preparation. Interestingly the partially folded intermediate regained significant tertiary structure/interactions, with increasing concentration of TFE, and at 60% (v/v) TFE approached almost that of the pseudo native (pH 7.0) state. Further increase to 70% (v/v) TFE, however, resulted in complete loss of tertiary structure/interactions. Studies on tryptophan fluorescence also suggested the induction of some compact structure at 60% (v/v) concentration of TFE. The partially folded intermediate showed enhanced binding of the fluorescent probe (ANS) in the presence of 60% (v/v) TFE. Taken together these observations suggest a "molten globule" state between 60 and 70% (v/v) TFE. Thermal transition studies in the near-UV CD region indicated cooperative transition for PFI in the presence of 60% (v/v) TFE changing to noncooperative transition at 70% (v/v) TFE. This was accompanied by a shift in the midpoint of thermal denaturation (T(m)) from 58 to 51 degrees C. Gradual transition and loss of cooperative thermal unfolding in the 60-70% (v/v) range of TFE also support the existence of the molten globule state.
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Affiliation(s)
- Pawan Gupta
- Department of Biochemistry, Faculty of Life Sciences, Aligarh Muslim University, Aligarh 202002, India
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15
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Whitten ST, Wooll JO, Razeghifard R, García-Moreno E B, Hilser VJ. The origin of pH-dependent changes in m-values for the denaturant-induced unfolding of proteins. J Mol Biol 2001; 309:1165-75. [PMID: 11399086 DOI: 10.1006/jmbi.2001.4726] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Denaturant-induced unfolding is one of the most prevalent means of evaluating the structural stability of proteins and of determining the energetic consequences of mutations or changes in solution conditions. In spite of the widespread use of this approach, controversies and inconsistencies still persist with regard to the interpretation of the results of such studies. For example, most proteins show either a significant increase or a decrease (as much as 100 %) in the denaturant-dependence of the free energy of unfolding (i.e. the m-value) under increasingly acidic conditions. The pH dependence of the m-value is given different interpretations depending on whether the m-values increase or decrease with decreasing pH. In cases where m-values decrease, the decrease is attributed to the presence of an intermediate that becomes transiently stabilized during the unfolding transition at low pH. Cases where m-values increase as pH is lowered are usually interpreted in terms of an increase in the amount of surface area exposed by the denatured state at low pH. We have developed a general thermodynamic model that accounts for both types of behavior in terms of an intermediate that is populated throughout the unfolding transition. The model provides a unified framework for explaining both types of observed behavior, and the validity of the model was tested through the analysis of the pH dependence of m-values of staphylococcal nuclease. According to the model, the observed increase in m-values with decreasing pH is consistent with the existence of an intermediate that is populated during urea and guanidine unfolding. The intermediate becomes less populated during the unfolding transition at lower pH values giving rise to the apparent increase in m-values. These results argue that the prevailing interpretation need not apply to all proteins.
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Affiliation(s)
- S T Whitten
- Department of Human Biological Chemistry and Genetics, and Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX 77555, USA
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16
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Whitten ST, García-Moreno E B. pH dependence of stability of staphylococcal nuclease: evidence of substantial electrostatic interactions in the denatured state. Biochemistry 2000; 39:14292-304. [PMID: 11087378 DOI: 10.1021/bi001015c] [Citation(s) in RCA: 115] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The pH dependence of stability of staphylococcal nuclease was studied with two independent equilibrium thermodynamic approaches. First, by measurement of stability in the pH range 9 to 3.5 by fluorescence-monitored denaturation with urea (Delta), GdnHCl (Delta), and heat (Delta). Second, by numerical integration of H(+) titration curves (Delta) measured potentiometrically under native (100 mM KCl) and unfolding (6.0 M GdnHCl) conditions. The pH dependence of stability described by Delta, Delta, and Delta was comparable but significantly different from the one described by Delta. The decrease in Delta between pH 9 and pH 4 was 4 kcal/mol greater than the decrease in Delta, Delta, and Delta in the same pH range. In 6 M GdnHCl, all the ionizable groups titrated with the pK(a) values of model compounds. Therefore, Delta represents the free energy difference between the native state (N) and an ensemble of unstructured, or expanded, and highly screened conformations. In contrast, the shallower pH dependence of stability described by Delta and by Delta between pH 9 and 5 was consistent with the titration of histidines with depressed, nativelike pK(a) values in the denatured state (D). These depressed pK(a) values likely reflect long-range electrostatic interactions with the other 29 basic groups and are a consequence of the compact character of the D state. The steep change in Delta and Delta at pH < 5 suggests that near pH 5 the structural and thermodynamic character of the D state shifts toward a state in which acidic residues titrate with normal pK(a) values, presumably because the electrostatic interactions with basic residues are lost, maybe as a consequence of an expansion.
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Affiliation(s)
- S T Whitten
- Department of Biophysics, Johns Hopkins University, Baltimore, Maryland 21218, USA
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17
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Filfil R, Chalikian TV. Volumetric and spectroscopic characterizations of the native and acid-induced denatured states of staphylococcal nuclease. J Mol Biol 2000; 299:827-42. [PMID: 10835287 DOI: 10.1006/jmbi.2000.3773] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have characterized the acid-induced denaturation of staphylococcal nuclease (SNase) at different urea concentrations by a combination of ultrasonic velocimetry, high precision densimetry, and CD spectroscopy. Our CD spectroscopic results suggest that, at low salt and acidic pH, the protein is unfolded with disrupted secondary and tertiary structures. Furthermore, as judged by far UV CD spectra, the protein is further unfolded at acidic pH upon the addition of urea up to the concentration of 1.5 M. The midpoint of the transition shifts to more neutral pH values and the cooperativity of the transition decreases as the acid-induced denaturation of SNase occurs at higher urea concentrations. We find that the change in volume, Deltav, accompanying the acid-induced denaturation of SNase increases from -0.013 cm(3) g(-1) (-218 cm(3) mol(-1)) in the absence of urea to 0.011 cm(3) g(-1) (185 cm(3) mol(-1)) at 1.5 M urea. At all urea concentrations, the partial specific adiabatic compressibility, k(o)(s), of the protein decreases upon its unfolding with the values of Deltak(o)(s) equal to -6.3x10(-6) (-0.106 cm(3) mol(-1) bar(-1)), -4.5x10(-6) (-0.076 cm(3) mol(-1) bar(-1)), -4.6x10(-6) (-0.077 cm(3) mol(-1) bar(-1)), and -3.8x10(-6) (-0.064 cm(3) mol(-1) bar(-1)) cm(3) g(-1) bar(-1) at urea concentrations of 0, 0.5, 1.0, and 1.5 M, respectively. In general, our volumetric results suggest that the acid-induced denatured state of SNase is only partially unfolded with the solvent-exposed surface area equal to 70-80 % of that expected for the fully extended conformation.
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Affiliation(s)
- R Filfil
- Department of Pharmaceutical Sciences, Faculty of Pharmacy, University of Toronto, 19 Russell Street, Toronto, Ontario, M5S 2S2, Canada
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18
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Lassalle MW, Yamada H, Akasaka K. The pressure-temperature free energy-landscape of staphylococcal nuclease monitored by (1)H NMR. J Mol Biol 2000; 298:293-302. [PMID: 10764598 DOI: 10.1006/jmbi.2000.3659] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The thermodynamic stability of staphylococcal nuclease was studied against the variation of both temperature and pressure by utilizing (1)H NMR spectroscopy at 750 MHz in 20 mM Mes buffer containing 99.9 % (2)H(2)O, pH 5.3. Equilibrium fractions of folded and unfolded protein species were evaluated with the proton signals of two histidine residues as monitor in the pressure range of 30-3300 bar and in the temperature range of 1.5 degrees C-35 degrees C. From the multi-parameter fit of the experimental data to the Gibbs energy equation expressed as a simultaneous function of pressure and temperature, we determined the compressibility change (Deltabeta), the volume change at 1 bar (DeltaV degrees ) and the expansivity change (Deltaalpha) upon unfolding among other thermodynamic parameters: Deltabeta=0.02(+/-0.003) ml mol(-1) bar(-1); Deltaalpha=1.33(+/-0.2) ml mol(-1) K(-1); DeltaV degrees =-41.9(+/-6. 3) ml mol(-1) (at 24 degrees C); DeltaG degrees =13.18(+/-2) kJ mol(-1) (at 24 degrees C); DeltaC(p)=13.12(+/-2) kJ mol(-1) K(-1); DeltaS degrees =0.32(+/-0.05) kJ mol(-1) K(-1 )(at 24 degrees C). The result yields a three-dimensional free energy surface, i.e. the free energy-landscape of staphylococcal nuclease on the P-T plane. The significantly positive Deltabeta and Deltaalpha values suggest that, in the pressure-denatured state, staphylococcal nuclease forms a loosely packed and fluctuating structure. The slight but statistically significant difference between the unfolding transitions of the His8 and His124 environments is considered to reflect local fluctuations in the native state, leading to pre-melting of the His124 environment prior to the cooperative unfolding of the major part of the protein.
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Affiliation(s)
- M W Lassalle
- Department of Molecular Science, Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai-cho, Kobe, Nada-ku, 657-8501, Japan
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19
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Muzammil S, Kumar Y, Tayyab S. Molten globule-like state of human serum albumin at low pH. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 266:26-32. [PMID: 10542047 DOI: 10.1046/j.1432-1327.1999.00810.x] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Human serum albumin (HSA), under conditions of low pH, is known to exist in two isomeric forms, the F form at around pH 4.0 and the E form below 3.0. We studied its conformation in the acid-denatured E form using far-UV and near-UV CD, binding of a hydrophobic probe, 1-anilinonaphthalene-8-sulfonic acid (ANS), thermal transition by far-UV and near-UV CD, tryptophan fluorescence, quenching of tryptophan fluorescence using a neutral quencher, acrylamide and viscosity measurements. The results show that HSA at pH 2.0 is characterized by a significant amount of secondary structure, as evident from far-UV CD spectra. The near-UV CD spectra showed a profound loss of tertiary structure. A marked increase in ANS fluorescence signified extensive solvent exposure of non-polar clusters. The temperature-dependence of both near-UV and far-UV CD signals did not exhibit a co-operative thermal transition. The intrinsic fluorescence and acrylamide quenching of the lone tryptophan residue, Trp214, showed that, in the acid-denatured state, it is buried in the interior in a non-polar environment. Intrinsic viscosity measurements showed that the acid-denatured state is relatively compact compared with that of the denatured state in 7 M guanidine hydrochloride. These results suggest that HSA at pH 2.0 represents the molten globule state, which has been shown previously for a number of proteins under mild denaturing conditions.
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Affiliation(s)
- S Muzammil
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, India
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20
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Kaushik JK, Bhat R. Thermal Stability of Proteins in Aqueous Polyol Solutions: Role of the Surface Tension of Water in the Stabilizing Effect of Polyols. J Phys Chem B 1998. [DOI: 10.1021/jp981119l] [Citation(s) in RCA: 183] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jai K. Kaushik
- Centre for Biotechnology, Jawaharlal Nehru University, New Delhi 110067, India
| | - Rajiv Bhat
- Centre for Biotechnology, Jawaharlal Nehru University, New Delhi 110067, India
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21
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Robertson AD, Murphy KP. Protein Structure and the Energetics of Protein Stability. Chem Rev 1997; 97:1251-1268. [PMID: 11851450 DOI: 10.1021/cr960383c] [Citation(s) in RCA: 506] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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22
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Eftink MR, Ramsay GD, Beavers A. Studies of the unfolding of an unstable mutant of staphylococcal nuclease: Evidence for low temperature unfolding and compactness of the high temperature unfolded state. Proteins 1997. [DOI: 10.1002/(sici)1097-0134(199706)28:2<227::aid-prot11>3.0.co;2-k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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23
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Hilser VJ, Townsend BD, Freire E. Structure-based statistical thermodynamic analysis of T4 lysozyme mutants: structural mapping of cooperative interactions. Biophys Chem 1997; 64:69-79. [PMID: 9127939 DOI: 10.1016/s0301-4622(96)02220-x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The recent development of a structural parameterization of the energetics of protein folding has permitted the incorporation of the functions that describe the enthalpy, entropy and heat capacity changes, i.e. the individual components of the Gibbs energy, into a statistical thermodynamic formalism that describes the distribution of conformational states under equilibrium conditions. The goal of this approach is to construct with the computer a large ensemble of conformational states, and then to derive the most probable population distribution, i.e. the distribution of states that best accounts for a wide array of experimental observables. This analysis has been applied to four different mutants of T4 lysozyme (S44A, S44G, V131A, V131G). It is shown that the structural parameterization predicts well the stability of the protein and the effects of the mutations. The entire set of folding constants per residue has been calculated for the four mutants. In all cases, the effect of the mutations propagates beyond the mutation site itself through sequence and three-dimensional space. This phenomenon occurs despite the fact that the mutations are at solvent-exposed locations and do not directly affect other interactions in the protein. These results suggest that single amino acid mutations at solvent-exposed locations, or other locations that cause a minimal perturbation, can be used to identify the extent of cooperative interactions. The magnitude and extent of these effects and the accuracy of the algorithm can be tested by means of NMR-detected hydrogen exchange.
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Affiliation(s)
- V J Hilser
- Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA
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24
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Eftink MR, Ionescu R. Thermodynamics of protein unfolding: questions pertinent to testing the validity of the two-state model. Biophys Chem 1997; 64:175-97. [PMID: 17029834 DOI: 10.1016/s0301-4622(96)02237-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/1996] [Accepted: 09/11/1996] [Indexed: 10/17/2022]
Abstract
We discuss a number of questions pertaining to the analysis of data to extract thermodynamic parameters for the reversible unfolding of proteins. Simulations are presented to illustrate problems in trying to test the validity of the two-state model, vis-a-vis a more complicated unfolding model. A conceptual and practical problem is how to consider the unfolded state and how to relate the observed signal to this state. We discuss the idea that the unfolded state can be described as a single macrostate, comprising a distribution of microstates having different degrees of solvent-accessible surface area. We also discuss the possibilities and thermodynamic consequences of having more than one unfolded state and of having a denaturant which both stabilizes and destabilizes the protein's native state.
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Affiliation(s)
- M R Eftink
- Department of Chemistry, University of Mississippi, University, MS 38677, USA
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25
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Makhatadze GI, Lopez MM, Privalov PL. Heat capacities of protein functional groups. Biophys Chem 1997; 64:93-101. [PMID: 17029831 DOI: 10.1016/s0301-4622(96)02234-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/1996] [Accepted: 09/13/1996] [Indexed: 10/18/2022]
Abstract
Using a precise technique of scanning calorimetry the heat capacities of a series of carboxylic acids and their sodium salts, alcohols, and N-substituted amides have been measured from 5 to 100 degrees C. From these data, the partial molar heat capacities of CH2, CONH, COOH, and COONa groups have been determined. It is shown that the heat capacity of the CH(2) group in aqueous solution is independent of the type of compound used for its determination, is positive at low temperature, and is linearly decreasing in magnitude with an increase in temperature. In contrast, the heat capacities of COOH and COONa groups in aqueous solution are negative at room temperature and their magnitude non-linearly decreases with an increase in temperature. It appears that the partial heat capacity of CONH group in aqueous solution depends on the type of model compound used for its determination. These differences correlate with the difference in the water accessible surface area of atoms in the CONH group in different model compounds.
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Affiliation(s)
- G I Makhatadze
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA.
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26
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Carra JH, Murphy EC, Privalov PL. Thermodynamic effects of mutations on the denaturation of T4 lysozyme. Biophys J 1996; 71:1994-2001. [PMID: 8889173 PMCID: PMC1233665 DOI: 10.1016/s0006-3495(96)79397-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
We investigated the folding of substantially destabilized mutant forms of T4 lysozyme using differential scanning calorimetry and circular dichroism measurements. Three mutations in an alpha-helix in the protein's N-terminal region, the alanine insertion mutations S44[A] and K48[A], and the substitution A42K had previously been observed to result in unexpectedly low apparent enthalpy changes of melting, compared to a pseudo-wild-type reference protein. The pseudo-wild-type reference protein thermally unfolds in an essentially two-state manner. However, we found that the unfolding of the three mutant proteins has reduced cooperativity, which partially explains their lower apparent enthalpy changes. A three-state unfolding model including a discrete intermediate is necessary to describe the melting of the mutant proteins. The reduction in cooperativity must be considered for accurate calculation of the energy changes of folding. Unfolding in two stages reflects the underlying two-subdomain structure of the lysozyme protein family.
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Affiliation(s)
- J H Carra
- Department of Biology and Biocalorimetry Center, Johns Hopkins University, Baltimore, Maryland 21218, USA.
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27
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Abstract
Human plasma apolipoprotein A-2 (apoA-2) is the second major protein of the high-density lipoproteins that mediate the transport and metabolism of cholesterol. Using CD spectroscopy and differential scanning calorimetry, we demonstrate that the structure of lipid-free apoA-2 in neutral low-salt solutions is most stable at approximately 25 degrees C and unfolds reversibly both upon heating and cooling from 25 degrees C. High-temperature unfolding of apoA-2, monitored by far-UV CD, extends from 25-85 degrees C with midpoint Th = 56 +/- 2 degrees C and vant Hoff's enthalpy delta H(Th) = 17 +/- 2 kcal/mol that is substantially lower than the expected enthalpy of melting of the alpha-helical structure. This suggests low-cooperativity apoA-2 unfolding. The apparent free energy of apoA-2 stabilization inferred from the CD analysis of the thermal unfolding, delta G(app)(25 degrees) = 0.82 +/- 0.15 kcal/mol, agrees with the value determined from chemical denaturation. Enhanced low-temperature stability of apoA-2 observed upon increase in Na2HPO4 concentration from 0.3 mM to 50 mM or addition of 10% glycerol may be linked to reduced water activity. The close proximity of the heat and cold unfolding transitions, that is consistent with low delta G(app)(25 degrees), indicates that lipid-free apoA-2 has a substantial hydrophobic core but is only marginally stable under near-physiological solvent conditions. This suggests that in vivo apoA-2 transfer is unlikely to proceed via the lipid-free state. Low delta H(Th) and low apparent delta Cp approximately 0.52 kcal/mol.K inferred from the far-UV CD analysis of apoA-2 unfolding, and absence of tertiary packing interactions involving Tyr groups suggested by near-UV CD, are consistent with a molten globular-like state of lipid-free apoA-2.
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Affiliation(s)
- O Gursky
- Department of Biophysics, Boston University School of Medicine, Massachusetts 02118, USA.
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28
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Poklar N, Vesnaver G, Lapanje S. Thermodynamics of denaturation of alpha-chymotrypsinogen A in aqueous urea and alkylurea solutions. JOURNAL OF PROTEIN CHEMISTRY 1995; 14:709-19. [PMID: 8747432 DOI: 10.1007/bf01886910] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The effects of pH, urea, and alkylureas on the thermal stability of alpha-chymotrypsinogen A (alpha-ctg A) have been investigated by differential scanning calorimetry (DSC) and UV spectroscopy. Heat capacity changes and enthalpies of transition of alpha-ctg A in the presence of urea and alkylureas were measured at the transition temperature. Using these data, the corresponding Gibbs free energies, enthalpies, and entropies of denaturation at 25 degrees C were calculated. Comparison of these values shows that at 25 degrees C denaturation with urea is characterized by a significantly smaller enthalpy and entropy of denaturation. At all denaturant concentrations the enthalpy term slightly dominates the entropy term in the Gibbs free energy function. The most obvious effect of alkylureas was lowering of the temperature of transition, which was increasing with alkylurea concentration and the size of alkyl chain. Destabilization of the folded protein in the presence of alkylureas appears to be primarily the result of the weakening of hydrophobic interactions due to diminished solvent ordering around the protein-molecules. At pH lower than 2.0, alpha-ctg A still exists in a very stable form, probably the acid-denatured from (A-form).
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Affiliation(s)
- N Poklar
- Department of Chemistry, University of Ljubljana, Slovenia
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29
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Myers JK, Pace CN, Scholtz JM. Denaturant m values and heat capacity changes: relation to changes in accessible surface areas of protein unfolding. Protein Sci 1995; 4:2138-48. [PMID: 8535251 PMCID: PMC2142997 DOI: 10.1002/pro.5560041020] [Citation(s) in RCA: 1444] [Impact Index Per Article: 49.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Denaturant m values, the dependence of the free energy of unfolding on denaturant concentration, have been collected for a large set of proteins. The m value correlates very strongly with the amount of protein surface exposed to solvent upon unfolding, with linear correlation coefficients of R = 0.84 for urea and R = 0.87 for guanidine hydrochloride. These correlations improve to R = 0.90 when the effect of disulfide bonds on the accessible area of the unfolded protein is included. A similar dependence on accessible surface area has been found previously for the heat capacity change (delta Cp), which is confirmed here for our set of proteins. Denaturant m values and heat capacity changes also correlate well with each other. For proteins that undergo a simple two-state unfolding mechanism, the amount of surface exposed to solvent upon unfolding is a main structural determinant for both m values and delta Cp.
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Affiliation(s)
- J K Myers
- Department of Biochemistry and Biophysics, Texas A&M University, College Station 77843, USA
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30
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Dill KA, Bromberg S, Yue K, Fiebig KM, Yee DP, Thomas PD, Chan HS. Principles of protein folding--a perspective from simple exact models. Protein Sci 1995; 4:561-602. [PMID: 7613459 PMCID: PMC2143098 DOI: 10.1002/pro.5560040401] [Citation(s) in RCA: 1174] [Impact Index Per Article: 40.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
General principles of protein structure, stability, and folding kinetics have recently been explored in computer simulations of simple exact lattice models. These models represent protein chains at a rudimentary level, but they involve few parameters, approximations, or implicit biases, and they allow complete explorations of conformational and sequence spaces. Such simulations have resulted in testable predictions that are sometimes unanticipated: The folding code is mainly binary and delocalized throughout the amino acid sequence. The secondary and tertiary structures of a protein are specified mainly by the sequence of polar and nonpolar monomers. More specific interactions may refine the structure, rather than dominate the folding code. Simple exact models can account for the properties that characterize protein folding: two-state cooperativity, secondary and tertiary structures, and multistage folding kinetics--fast hydrophobic collapse followed by slower annealing. These studies suggest the possibility of creating "foldable" chain molecules other than proteins. The encoding of a unique compact chain conformation may not require amino acids; it may require only the ability to synthesize specific monomer sequences in which at least one monomer type is solvent-averse.
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Affiliation(s)
- K A Dill
- Department of Pharmaceutical Chemistry, University of California, San Francisco 94143-1204, USA
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31
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Eftink MR. Use of multiple spectroscopic methods to monitor equilibrium unfolding of proteins. Methods Enzymol 1995; 259:487-512. [PMID: 8538469 DOI: 10.1016/0076-6879(95)59058-7] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- M R Eftink
- Department of Chemistry, University of Mississippi, University 38677, USA
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32
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Affiliation(s)
- G I Makhatadze
- Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA
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33
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Xie D, Fox R, Freire E. Thermodynamic characterization of an equilibrium folding intermediate of staphylococcal nuclease. Protein Sci 1994; 3:2175-84. [PMID: 7756977 PMCID: PMC2142756 DOI: 10.1002/pro.5560031203] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
High-sensitivity differential scanning calorimetry and CD spectroscopy have been used to probe the structural stability and measure the folding/unfolding thermodynamics of a Pro117-->Gly variant of staphylococcal nuclease. It is shown that at neutral pH the thermal denaturation of this protein is well accounted for by a 2-state mechanism and that the thermally denatured state is a fully hydrated unfolded polypeptide. At pH 3.5, thermal denaturation results in a compact denatured state in which most, if not all, of the helical structure is missing and the beta subdomain apparently remains largely intact. At pH 3.0, no thermal transition is observed and the molecule exists in the compact denatured state within the 0-100 degrees C temperature interval. At high salt concentration and pH 3.5, the thermal unfolding transition exhibits 2 cooperative peaks in the heat capacity function, the first one corresponding to the transition from the native to the intermediate state and the second one to the transition from the intermediate to the unfolded state. As is the case with other proteins, the enthalpy of the intermediate is higher than that of the unfolded state at low temperatures, indicating that, under those conditions, its stabilization must be of an entropic origin. The folding intermediate has been modeled by structural thermodynamic calculations. Structure-based thermodynamic calculations also predict that the most probable intermediate is one in which the beta subdomain is essentially intact and the rest of the molecule unfolded, in agreement with the experimental data. The structural features of the equilibrium intermediate are similar to those of a kinetic intermediate previously characterized by hydrogen exchange and NMR spectroscopy.
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Affiliation(s)
- D Xie
- Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA
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34
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Carra JH, Anderson EA, Privalov PL. Thermodynamics of staphylococcal nuclease denaturation. II. The A-state. Protein Sci 1994; 3:952-9. [PMID: 8069224 PMCID: PMC2142886 DOI: 10.1002/pro.5560030610] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Staphylococcal nuclease, at low pH and in the presence of high salt concentrations, has previously been proposed to exist in a partially folded or molten globule form called the "A-state" (Fink et al., 1993, Protein Sci 2:1155-1160). We have found that the A-state of nuclease at pH 2.1 in the presence of moderate to high salt concentrations and at low temperature exists in a substantially folded form structurally more similar to a native state. The A-state has the far-UV circular dichroism spectra characteristic of the native protein, which indicates that it has a large degree of secondary structure. Upon heating, the A-state denatures with a sigmoidal change in far-UV ellipticity and an observable peak in a differential scanning calorimeter trace, indicating that it is thermodynamically distinct from the denatured state. Three different mutations in a residue normally buried in the protein's core stabilize or destabilize the A-state in the same way as they affect the denaturation of the native state. The A-state must, therefore, contain at least some tertiary packing of side chains. Unlike the native state, which shows cold denaturation at low temperatures, the A-state is most stable at temperatures below 0 degrees C.
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Affiliation(s)
- J H Carra
- Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218
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