Effect of hapten binding on antibody-water interaction. A concept of fluctuating cavities

Abstract

Solutions of pig anti-Dnp antibodies, Fab and Fc fragments, human IgG, human serum albumin and cytochrome c were examined by infrared spectroscopy with the aim to investigate the influence of these proteins on the surrounding water. Anti-Dnp antibodies, human IgG and oxidized cytochrome c induced a shift of the maximum of the deformation—liberation band of water towards lower wave numbers. Anti-Dnp antibodies complexed with hapten, free and haptenated Fab fragments, reduced cytochrome c and serum albumin induced a shift of the maximum to higher wave numbers, while Fc fragment did not induce any significant shift. Perturbating agents such as 0.5 M sodium chloride and 20% saccharose caused a shift of the maximum of water in protein solutions to higher wave numbers. The observed phenomena are interpreted in terms of the ability of cavities and clefts in proteins such as immunoglobulins to fluctuate between two states, more or less accessible to water. This ability is thought to result in a generation of anisotropic fluctuations in the surrounding water medium, associated with lowering of the number and/or strength of hydrogen bonds between water molecules. Proteins lacking cavities or clefts affect the water medium in an opposite way; the hydrogen bond network of water becomes more firm and consolidated. Binding of hapten to the intact antibody apparently alters the domain oscillations and the geometry of the antibody molecule. Consequently in contrast to free antibody, the antibody—hapten complex consolidates the hydrogen bond network of surrounding water.