Assessing Weak Anion Binding to Small Peptides.

Area of Science:

• Biochemistry
• Chemical Physics
• Spectroscopy

Background:

• Hofmeister effects describe how salts influence protein properties through water-salt and direct salt-protein interactions.
• Direct salt-protein interactions are weak and difficult to quantify, often considered nonspecific.
• Understanding these interactions is crucial for controlling protein behavior in various applications.

Purpose of the Study:

• To demonstrate the utility of 1H NMR spectroscopy for assessing weak anion binding to peptides.
• To quantify anion binding affinity using N-H signal shifts.
• To elucidate the binding mechanism and location of anion-peptide interactions.

Main Methods:

• Utilized pentapeptides as model systems.
• Employed the H-dimension of nuclear magnetic resonance (NMR) spectroscopy to measure N-H signal shifts.
• Analyzed shifts induced by anion association and point mutations.
• Performed molecular dynamics (MD) simulations to support experimental findings.

Main Results:

• Observed significant upfield N-H signal shifts upon anion association, indicating binding.
• Demonstrated that these shifts are larger than those from ionic strength effects.
• Found that anion binding is weak, with anions associating mainly with nonpolar peptide regions.
• MD simulations corroborated the preferential interaction with nonpolar regions over amide groups.

Conclusions:

• 1H NMR spectroscopy is a powerful tool for quantifying low-affinity anion binding to peptides.
• Anion binding to peptides is primarily driven by interactions with nonpolar regions.
• These findings provide a benchmark for studying anion binding in more complex biological systems and understanding Hofmeister effects.