Hofmeister Ion-Induced Changes in Water Structure Correlate with Changes in Solvation of an Aggregated Protein Complex

Abstract

RecA is a naturally aggregating Escherichia coli protein that catalyzes the strand exchange reaction utilized in DNA repair. Previous studies have shown that the presence of salts influence RecA activity, aggregation, and stability and that salts stabilize RecA in an inverse-anionic Hofmeister series. Here we utilized attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and circular dichroism (CD) to investigate how various Hofmeister salts alter the water structure and RecA solvation and aggregation. Spectroscopic studies performed in water and deuterium oxide suggest that salts alter water O-(1)H and O-(2)H stretch and bend vibrations as well as protein amide I (or I') and amide II (or II') vibrations. Anions have a much larger influence on water vibrations than cations. Water studies also show increased water-water and/or water-ion interactions in the presence of strongly hydrated SO4(2-) salts and evidence for decreased interactions with weakly hydrated Cl(-) and ClO4(-) salts. Salt-water difference infrared spectra show that kosmotropic salts are more hydrated than chaotropic salts. Interestingly, this is the opposite trend to the changes in protein solvation. Infrared spectra of RecA show that vibrations associated with protein desolvation were observed in the presence of SO4(2-) salts. Conversely, vibrations associated with protein solvation were observed in the presence of Cl(-) and ClO4(-) salts. Difference infrared studies on the dehydration of model proteins aided in identifying changes in RecA-solvent interactions. This study provides evidence that salt-induced changes in water vibrations correlate to changes in protein solvent interactions and thermal stability.

Isomers and energy landscapes of micro-hydrated sulfite and chlorate clusters

“…Ions can be classified according to the Hofmeister series, which orders ions according to their ability to desolvate proteins [1][2][3][4][5]. The ions which promote disorder within the hydrogen-bonding network of water and disrupt protein stability are labelled as chaotropes, while ions which promote long-range order and protein stability within water are classified as kosmotropes [1,2,6].…”

Isomers and Energy Landscapes of Perchlorate–Water Clusters and a Comparison to Pure Water and Sulfate–Water Clusters

“…3,4,5,7 Understanding the Hofmeister series is important because its effects can be seen in many different systems including industrial processes and atmospheric chemistry as well as in biology. [8][9][10] In previous work, we have studied the sulfate ion (SO 4 where σ ij and ε ij are the Lennard-Jones distance and energy parameters, r ij is the inter-site separation, and q i and q j are the charges of sites i and j, respectively.…”

Raman spectroscopy of alkali halide hydration: hydrogen bond relaxation and polarization

“…Water can easily dissolve inorganic salts into ions, and the solute–solvent molecular interaction has striking impact on processes of biological, biomedical, and chemical, such as the solubility and stability of proteins and nucleic acids, drug delivery in human body, cellular signaling, dissociation and self‐assembly of soft mater, liquid skin stress and viscosity, supercapacitor performance, as well as decontamination of the metal‐containing waste . According to their abilities to salt in or salt out proteins in aqueous solutions, ions were ranked by Franz Homeister in 1888 in the following order: SO 4 2− > HPO 4 2− > OH − > F − > HCOO − > Cl − > Br − > NO 3 − > I − > SCN − > ClO 4 − , and Cs + > NH 4 + > Rb + > K + > Na + > Li + > Mg 2+ > Ca 2+ > Ba 2+ .…”