A computational study of the effect of matrix structural order on water sorption by Trp-cage miniproteins.

We present the first simulation study of the impact of protein matrix structure on water sorption along with a new computational method to hydrate and dehydrate protein systems reversibly. To understand the impact of the underlying structure of the protein matrix on the hydration process, we compare three types of protein substrates comprised of Trp-cage miniproteins with varying degrees of monomer translational and orientational order and monomer denaturation. We show that the water sorption isotherms are qualitatively and quantitatively very similar for the Trp-cage matrices independently of the underlying degree of disorder, which is consistent with the experimental observation that the qualitative features of water sorption isotherms are nearly universal for globular proteins. We also show that the Trp-cage matrices with varying disorder share similar trends in volumetric swelling, solvent accessibility, and protein-water hydrogen bonding during the sorption processes, while hydrogen bonding between protein molecules depends sensitively on the matrix characteristics (crystal, powder, and thermally denatured powder). Volumetric swelling, solvent accessibility, and protein-water hydrogen bonds exhibit no hysteresis when plotted as a function of hydration level and are thus controlled exclusively by the protein's water content.