Molecular Dynamics and Multinuclear Magnetic Resonance Studies of Zwitterions and Proteins in Concentrated Solutions

Abstract

Multinuclear spin relaxation observations were carried out for concentrated protein solutions, such as lysozyme, myosin or soy globulins. Ion-specific effects were observed and analyzed with thermodynamic linkage models involving reversible binding of hydrated ions. Molecular dynamics and multinuclear spin relaxation measurements were carried out for several proteins in order to elucidate the mechanisms for the cationic and anionic interactions with the protein binding sites. Specific interactions of the anions with the positively charged side chain groups of lysine, arginine and histidine, as well as nonspecific binding to amide groups, were found. Both anion- and cation- specific, as well as cooperative, interactions with charged side chain groups were found for myosin, tropomyosin, and for 7S and 11S globulins from soy. The comparison between the 17O and 23Na NMR results strongly suggests that water is exchanged as the hydrated ion species between the myofibrillar and/or myosin protein binding sites and the bulk, aqueous solution of electrolytes.