Thermodynamic modeling and experimental data reveal that sugars stabilize proteins according to an excluded volume mechanism

We present a new thermodynamic model to investigate therelativeeffects of excluded volume and soft interaction contributions in determiningwhether a cosolute will either destabilize or stabilize a proteinin solution. This model is unique in considering an atomisticallydetailed model of the protein and accounting for the preferentialaccumulation/exclusion of the osmolyte molecules from the proteinsurface. Importantly, we use molecular dynamics simulations and experimentsto validate the model. The experimental approach presents a uniquemeans of decoupling excluded volume and soft interaction contributionsusing a linear polymeric series of cosolutes with different numbersof glucose subunits, from 1 (glucose) to 8 (maltooctaose), as wellas an 8-mer of glucose units in the closed form (& gamma;-CD). By studyingthe stabilizing effect of cosolutes along this polymeric series usinglysozyme as a model protein, we validate the thermodynamic model andshow that sugars stabilize proteins according to an excluded volumemechanism.