Cation-Specific Influences on the Solvation and Solvent Accessibility of Alanine-Rich Peptides

Abstract

Studies in our lab correlated salt-induced changes in protein solvation to changes in water structure, protein aggregation and thermal stability. In order to better isolate and identify how salts influence protein structure and solvation, we extended our studies to include small peptides. Previous studies with alanine-rich peptides have correlated co-solvent-induced changes in solvation with stability. We utilized Attenuated Total Reflectance infrared spectroscopy (ATR-FTIR) and circular dichroism (CD) to study salt-induced changes in these peptides in 1H2O and 2H2O. Our data suggests ion-specific changes that reflect differences in peptide structure and/or solvation. CD spectra show significant secondary structure changes, particularly of the uncapped peptide, in the presence of some salts. These structural changes correlate with infrared experiments performed on partially dehydrated peptide thin films that show differences in the structure and 1H/2H exchange of the peptides. The 1H/2H exchange experiments show some salts alter peptide solvation and suggest changes in the solvent accessibility of the peptide. Peptide infrared data also show specific cation interactions to the peptide backbone. Furthermore, our data suggest cations preferentially influence solvation in an order consistent with the Hofmeister series, with Ca2+ and Mg2+ showing the most significant changes in peptide solvation.