Electrostatic Exploration of Biomolecular Interfaces: The Chemical Function of Interfacial Water
This chapter explores the dielectric structure of interfacial water that envelopes a soluble protein. The most striking feature arising from this epistructural analysis is the breakdown of the Debye ansatz that postulates the alignment of water polarization with the protein electrostatic field. The complexities of biological interfaces are shown to be in good measure due to this departure from the standard dielectric picture that has been historically extrapolated from the bulk interface. Accordingly, concepts like the permittivity coefficient are shown to be inadequate or at best insufficient to describe the interfacial dielectrics. The departure from bulk-like behavior is shown to enhance the physicochemical inhomogeneity of protein surfaces and enable their chemical functionality. The epistructural analysis identifies a structural defect known as dehydron as the causative of anomalous polarization effects that bring about the breakdown of the Debye standard picture. The epistructural analysis in the previous chapter revealed that interfacial tension is a central thermodynamic factor driving biomolecular events and may be stored as the electrostatic energy associated with the non-Debye component of water polarization. This chapter refines and completes this line of thought by showing that dehydrons locally induce interface basicity as a consequence of the promoted departure from Debye dielectrics. In this way, we delineate a chemical role for dehydrons as triggers of proton transfer events that enhance the nucleophilicity of enzymatically active groups nearby.
KeywordsInterfacial Tension Protein Data Bank Interfacial Water Packing Defect Residue Type
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