Protein crowding impedes pressure-induced unfolding of staphylococcal nuclease

► We measure high-pressure Trp-fluorescence spectra of staphylococcal nuclease (SNase). ► We examine three SNase samples in the presence of crowding agents. ► All the samples exhibit a two-state behavior (native and unfolded states). ► We find SNase unfolding as a function of pressure is impeded in crowded solutions. ► The result suggests this crowding effect may also apply to the proteins in cells.