Dataset Information

Thermodynamics of the Binding of Lysozyme to a Dendritic Polyelectrolyte: Electrostatics Versus Hydration.

ABSTRACT: The interaction between dendritic polyglycerol sulfate (dPGS) of the second generation and lysozyme was studied by isothermal titration calorimetry (ITC) at different temperatures and salt concentrations. Analysis by ITC showed that 2-3 lysozyme molecules were bound to each dPGS. The resulting binding constant K b and the Gibbs free energy ?G o decreased markedly with increasing salt concentration but were nearly independent of temperature. The salt dependence of K b led to the conclusion that ca. 3 counterions bound to dPGS were released upon complex formation. The gain in entropy ?G ci by this counterion-release scales logarithmically with salt concentration and is the main driving force for binding. The temperature dependence of ?G o was analyzed by the nonlinear van't Hoff plot, taking into account a finite heat capacity change ?C p,vH. This evaluation led to the binding enthalpy ?H vH and the binding entropy ?S vH. Both quantities varied strongly with temperature and even changed sign, but they compensated each other throughout the entire range of temperature. Coarse-grained computer simulations with explicit salt and implicit water were used to obtain the binding free energies that agreed with ITC results. Thus, electrostatic factors were the driving forces for binding whereas all hydration contributions leading to the strongly varying ?H vH and ?S vH canceled out. The calorimetric enthalpy ?H ITC measured directly by ITC differed largely from ?H vH. ITC measurements done in two buffer systems with different ionization enthalpies revealed that binding was linked to buffer ionization and a partial protonation of the protein.

SUBMITTER: Ran Q

PROVIDER: S-EPMC6644519 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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Thermodynamics of the Binding of Lysozyme to a Dendritic Polyelectrolyte: Electrostatics Versus Hydration.

Ran Qidi Q Xu Xiao X Dzubiella Joachim J Haag Rainer R Ballauff Matthias M

ACS omega 20180814 8

The interaction between dendritic polyglycerol sulfate (dPGS) of the second generation and lysozyme was studied by isothermal titration calorimetry (ITC) at different temperatures and salt concentrations. Analysis by ITC showed that 2-3 lysozyme molecules were bound to each dPGS. The resulting binding constant K b and the Gibbs free energy ΔG o decreased markedly with increasing salt concentration but were nearly independent of temperature. The salt dependence ...[more]

PMID: 31459043

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Project description:Actomyosin is an important molecular motor, and the binding of actin and myosin is an essential research target in biophysics. Nevertheless, the physical factors driving or opposing the binding are still unclear. Here, we investigate the role of water in actin-myosin binding using the most reliable statistical-mechanical method currently available for assessing biomolecules immersed in water. This method is characterized as follows: water is treated not as a dielectric continuum but as an ensemble of molecules; the polyatomic structures of proteins are taken into consideration; and the binding free energy is decomposed into physically insightful entropic and energetic components by accounting for the hydration effect to its full extent. We find that the actin-myosin binding brings large gains of electrostatic and Lennard-Jones attractive interactions. However, these gains are accompanied by even larger losses of actin-water and myosin-water electrostatic and LJ attractive interactions. Although roughly half of the energy increase due to the losses is cancelled out by the energy decrease arising from structural reorganization of the water released upon binding, the remaining energy increase is still larger than the energy decrease brought by the gains mentioned above. Hence, the net change in system energy is positive, which opposes binding. Importantly, the binding is driven by a large gain of configurational entropy of water, which surpasses the positive change in system energy and the conformational entropy loss occurring for actin and myosin. The principal physical origin of the large water-entropy gain is as follows: the actin-myosin interface is closely packed with the achievement of high shape complementarity on the atomic level, leading to a large increase in the total volume available to the translational displacement of water molecules in the system and a resultant reduction of water crowding (i.e., entropic correlations among water molecules).

Dataset Information

Thermodynamics of the Binding of Lysozyme to a Dendritic Polyelectrolyte: Electrostatics Versus Hydration.

Publications

Thermodynamics of the Binding of Lysozyme to a Dendritic Polyelectrolyte: Electrostatics Versus Hydration.

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