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| Alan Cooper - | |
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Microcalorimetry of Protein-Ligand Interactions
Alan Cooper
Chemistry Department, Glasgow University, Glasgow G12 8QQ
The thermodynamic forces that control biomolecular interactions in solution can now be measured directly using microcalorimetric methods, and a large body of empirical data is now available for protein folding, protein-ligand and protein-protein interactions. Most physico-chemical processes have an associated heat effect and microcalorimetry can now be used routinely both for straightforward analytical applications as well as for more fundamental studies of underlying thermodynamic principles. Examples will include the use of differential scanning calorimetry (DSC) and isothermal titration calorimetry (ITC) for the study of protein-protein and protein-ligand binding, and the recently introduced technique of pressure perturbation calorimetry (PPC) which is giving new information about hydration changes in biomolecular processes. Two general features are emerging from studies on a wide variety of systems: (i) the thermodynamics are frequently dominated by large heat capacity ( Cp) effects, with a consequent strong temperature dependence for H0 and S0 ; (ii) entropy and enthalpy values vary enormously in response to experimental conditions or mutagenesis, but in a compensatory fashion that leads to much smaller changes in free energy. Such H-S compensation constitutes a form of 'thermodynamic homeostasis' that may be of biological significance, but represents a major challenge to modeling and understanding the forces involved. Conventionally, these large Cp effects have been ascribed to hydrophobic interactions and changes in accessible non-polar surface areas. However, more recently we have shown that both Cp and entropy-enthalpy compensation effects are a much more general property of macromolecular systems comprising a multiplicity of weak, cooperative interactions. Thermodynamic models based on cooperative hydrogen-bonded lattices can reproduce these observations very effectively.
References:
A. Cooper, Heat capacity of hydrogen-bonded networks: an alternative view of protein folding thermodynamics, Biophys. Chem. (2000) 85, 25-39.
A. Cooper, C.M. Johnson, J.H. Lakey, M. Nöllmann, Heat does not come in different colours: entropy-enthalpy compensation, free energy windows, quantum confinement, pressure perturbation calorimetry, solvation and the multiple causes of heat capacity effects in biomolecular interactions, Biophys.Chem. (2001) 93, 215-230.
C. Clarke, R. J. Woods, J. Gluska, A. Cooper, M. A. Nutley, G. J. Boons, Involvement of water in carbohydrate-protein binding, J. Am. Chem. Soc. (2001) 123, 12238-12247.
H-I. Jung, A. Cooper, R.N. Perham, Interactions of the peripheral subunit-binding domain of the dihydrolipoyl acetyltransferase component in the assembly of the pyruvate dehydrogenase multienzyme complex of Bacillus stearothermophilus. Eur. J.Biochem. (2003) 270, 4488-4496.
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