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  • 1
    Electronic Resource
    Electronic Resource
    Configurational effects in antibody-antigen interactions studied by microcalorimetry (1995)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 21 (1995), S. 83-90 
    Details
    ISSN: 0887-3585
    Keywords: cytochrome c ; thermodynamics ; antibody binding ; microcalorimetry ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In this paper we study the binding of two monoclonal antibodies, E3 and E8, to cytochrome c using high-sensitivity isothermal titration calorimetry. We combine the calorimetric results with empirical calculations which relate changes in heat capacity to changes in entropy which arise from the hydrophobic effect. The change in heat capacity for binding E3 is -350 ± 60 cal K-1 mol-1 while for E8 it is -165 ± 40 cal K-1 mol-1. This result indicates that the hydrophobic effect makes a much larger contribution for E3 than for E8. Since the total entropy change at 25°C is very similar for both antibodies, it follows that the configurational entropy cost for binding E3 is much larger than for binding E8 (-77 ± 15 vs. -34 ± 11 cal K-1 mol-1). These results illustrate a case of entropy compensation in which the cost of restricting conformational degrees of freedom is to a large extent compensated by solvent release. We also show that the thermodynamic data can be used to make estimates of the surface area changes that occur upon binding. The results of the present study are consistent with previous hydrogen-deuterium exchange data, detected using 2D NMR, on the two antibody-antigen interactions. The NMR study indicated that protection from exchange is limited to the binding epitope for E8, but extends beyond the epitope for E3. These results were interpreted as suggesting that a larger surface area was buried on cytochrome c upon binding to E3 than to E8, and that larger changes in configurational entropy occur upon binding of E3 than E8. These findings are confirmed by the present study using isothermal titration calorimetry. © 1995 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340210202
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The enthalpy change in protein folding and binding: Refinement of parameters for structure-based calculations (1996)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 26 (1996), S. 123-133 
    Details
    ISSN: 0887-3585
    Keywords: enthalpy ; thermodynamics ; folding/unfolding ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Two effects are mainly responsible for the observed enthalpy change in protein unfolding: the disruption of internal interactions within the protein molecule (van der Waals, hydrogen bonds, etc.) and the hydration of the groups that are buried in the native state and become exposed to the solvent on unfolding. In the traditional thermodynamic analysis, the effects of hydration have usually been evaluated using the thermodynamic data for the transfer of small model compounds from the gas phase to water. The contribution of internal interactions, on the other hand, are usually estimated by subtracting the hydration effects from the experimental enthalpy of unfolding. The main drawback of this approach is that the enthalpic contributions of hydration, and those due to the disruption of internal interactions, are more than one order of magnitude larger than the experimental enthalpy value. The enthalpy contributions of hydration and disruption of internal interactions have opposite signs and cancel each other almost completely resulting in a final value that is over 10 times smaller than the individual terms. For this reason, the classical approach cannot be used to accurately predict unfolding enthalpies from structure: any error in the estimation of the hydration enthalpy will be amplified by a factor of 10 or more in the estimation of the unfolding enthalpy. Recently, it has been shown that simple parametric equations that relate the enthalpy change with certain structural parameters, especially changes in solvent accessible surface areas have considerable predictive power. In this paper, we provide a physical foundation to that parametrization and in the process we present a system of equations that explicitly includes the enthalpic effects of the packing density between the different atoms within the protein molecule. Using this approach, the error in the prediction of folding/unfolding enthalpies at 60°C, the median temperature for thermal unfolding, is better than ±3% (standard deviation = 4 kcal/mol). © 1996 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Entropy in biological binding processes: Estimation of translational entropy loss (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 63-67 
    Details
    ISSN: 0887-3585
    Keywords: entropy ; thermodynamics ; binding energetics ; translational entropy ; macromolecular interactions ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The loss of translational degrees of freedom makes an important, unfavorable contribution to the free energy of binding. Examination of experimental values suggest that calculation of this entropy using the Sackur-Tetrode equation produces largely overestimated values. Better agreement is obtained using the cratic entropy. Theoretical considerations suggest that the volumes available for the movement of a ligand in solution and in a complex are rather similar, suggesting also that the cratic entropy provides the best estimate of the loss of translational entropy. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340180108
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  • 4
    Electronic Resource
    Electronic Resource
    Structural energetics of peptide recognition: Angiotensin II/antibody binding (1993)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 15 (1993), S. 113-120 
    Details
    ISSN: 0887-3585
    Keywords: thermodynamics ; calorimetry ; protein-hormone interaction ; drug design ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The ability to predict the strength of the association of peptide hormones or other ligands with their protein receptors is of fundamental importance in the fields of protein engineering and rational drug design. To form a tight complex between a flexible peptide hormone and its receptor, the large loss of configurational entropy must be overcome. Recently, the crystallographic structure of the complex between angiotensin II and the Fab fragment of a high affinity monoclonal antibody has been determined (Garcia, K. C., Ronco, P. M., Verroust, P. J., Brünger, A. T., Amzel, L. M. Three-dimensional structure of an angiotensin II-Fab complex at 3 Å: Hormone recognition by an anti-idiotypic antibody. Science 257:502-507, 1992). In this paper we present a study of the thermodynamics of the association by high sensitivity isothermal titration calorimetry. The results of the experiments indicate that at 30°C the binding is characterized by (1) a ΔH of -8.9 ± 0.7 kcal mol-1, (2) a ΔCp of -240 ± 20 cal K-1 mol-1, and (3) the release of 1.1 ± 0.1 protons per binding site in the pH range 6.0-7.3. Using these values and the previously determined binding constant in phosphate buffer, ΔG at 30°C is estimated as -11 kcal mol-1 and ΔS as 6.9 cal K-1 mol-1. The calorimetric data indicate that binding is favored both enthalpically and entropically. These results have been complemented by structural thermodynamic calculations. The calculated and experimentally determined thermodynamic quantities are in good agreement. Entropically, the loss of configurational entropy is more than compensated by the entropy gain from solvent release associated with the hydrophobic effect. Enthalpically, binding is favored by polar interactions (hydrogen bonding). Consequently, the problem of binding flexible hormones is solved in much the same way as the folding of an unstructured polypeptide chain into a globular protein. © 1993 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340150203
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  • 5
    Electronic Resource
    Electronic Resource
    The heat capacity of proteins (1995)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 22 (1995), S. 404-412 
    Details
    ISSN: 0887-3585
    Keywords: protein thermodynamics ; protein folding ; protein stability ; protein thermodynamics ; energetics ; protein design ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The heat capacity plays a major role in the determination of the energetics of protein folding and molecular recognition. As such, a better understanding of this thermodynamic parameter and its structural origin will provide new insights for the development of better molecular design strategies. In this paper we have analyzed the absolute heat capacity of proteins in different conformations. The results of these studies indicate that three major terms account for the absolute heat capacity of a protein: (1) one term that depends only on the primary or covalent structure of a protein and contains contributions from vibrational frequencies arising from the stretching and bending modes of each valence bond and internal rotations; (2) a term that contains the contributions of noncovalent interactions arising from secondary and tertiary structure; and (3) a term that contains the contributions of hydration. For a typical globular protein in solution the bulk of the heat capacity at 25°C is given by the covalent structure term (close to 85% of the total). The hydration term contributes about 15 and 40% to the total heat capacity of the native and unfolded states, respectively. The contribution of non-covalent structure to the total heat capacity of the native state is positive but very small and does not amount to more than 3% at 25°C. The change in heat capacity upon unfolding is primarily given by the increase in the hydration term (about 95%) and to a much lesser extent by the loss of noncovalent interactions (up to ∼5%). It is demonstrated that a single universal mathematical function can be used to represent the partial molar heat capacity of the native and unfolded states of proteins in solution. This function can be experimentally written in terms of the molecular weight, the polar and apolar solvent accessible surface areas, and the total area buried from the solvent. This unique function accurately predicts the different magnitude and temperature dependences of the heat capacity of both the native and unfolded states, and therefore of the heat capacity changes associated with folding/unfolding transitions. © 1995 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340220410
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