Ion-Pairing Propensity in Guanidinium Salts Dictates Their Protein (De)stabilization Behavior

Area of Science:

• Protein science
• Biophysical chemistry
• Spectroscopy

Background:

• Guanidinium (Gdm) salts exhibit contrasting effects on protein structure.
• GdmCl is a known protein denaturant, while Gdm2SO4 has minimal impact.
• The role of ion pairing in these effects lacks extensive experimental validation.

Purpose of the Study:

• To experimentally validate the hypothesis that ion pairing dictates the effect of guanidinium salts on proteins.
• To investigate the contrasting effects of GdmCl and Gdm2SO4 on a model amide molecule, N-methylacetamide (NMA).

Main Methods:

• Combined electrochemical impedance spectroscopy (EIS) and THz spectroscopy.
• Molecular dynamics (MD) simulations.
• Analysis of ion hydration and ion-water rattling modes.

Main Results:

• MD simulations predicted heteroion pairing in Gdm2SO4, hindering Gdm+ interaction with NMA.
• GdmCl showed direct interaction between Gdm+ ions and NMA.
• THz spectroscopy confirmed these findings through analysis of ion-water dynamics.

Conclusions:

• The propensity of ion pairing in guanidinium salts is the key factor determining their protein (de)stabilization.
• Experimental evidence supports the role of ion pairing in modulating guanidinium salt effects on biomolecules.