Evaluation of interaction between histidine binding Cu2+ ion and histidine by atomic force microscopy

Area of Science:

• Biophysics
• Chemical Physics
• Materials Science

Background:

• Understanding biomolecular interactions is crucial for molecular biology and drug development.
• Atomic Force Microscopy (AFM) is a powerful tool for probing forces at the nanoscale.
• Histidine's role in protein structure and metal ion binding necessitates precise interaction force measurements.

Purpose of the Study:

• To directly measure the interaction forces between histidine molecules.
• To investigate the influence of copper ions (Cu2+) on histidine-histidine interactions.
• To explore the potential of AFM force-distance curves for quantifying biomolecular affinities.

Main Methods:

• Utilizing AFM force-distance curve measurements with histidine-modified cantilevers and substrates.
• Performing measurements under varying conditions, including the presence and absence of Cu2+ ions.
• Analyzing force curves using Gaussian curve fitting to determine adhesion forces.

Main Results:

• A significant adhesion force of 110 pN was observed between histidine molecules in the presence of Cu2+.
• In the absence of Cu2+ (or upon its chelation with EDTA), the measured adhesion force approached 0 pN.
• Direct histidine-histidine interaction is minimal without a bridging ionic component.

Conclusions:

• Direct histidine-histidine interaction is weak and requires bridging ions, such as Cu2+, for substantial adhesion.
• AFM force-distance curve analysis offers a viable method for directly measuring chemical affinities between biomolecules.
• This technique can elucidate the critical role of bridging ions in molecular interactions.