Effects of Discrete Protein-Surface Interactions in Scanning Force Microscopy Adhesion Force Measurements.

Area of Science:

• Biophysics
• Surface Science
• Molecular Interactions

Background:

• Scanning force microscopy (SFM) is used to measure molecular recognition forces.
• Discontinuities in SFM force-displacement curves are typically attributed to specific bond breaking.
• Accurate interpretation of SFM data is crucial for understanding molecular binding events.

Purpose of the Study:

• To investigate the cause of discontinuities in SFM force-displacement curves.
• To determine if nonspecific interactions contribute to observed force curve anomalies.
• To clarify the interpretation of molecular recognition measurements using SFM.

Main Methods:

• Utilized a scanning force microscope (SFM) to study molecular recognition.
• Employed a system with surface-immobilized antifluorescyl IgG and SFM probe-bound fluorescein ligands.
• Analyzed force-displacement curves, focusing on discontinuities and adhesion phenomena.

Main Results:

• Observed intermittent discontinuities in SFM force-displacement curves.
• Attributed these discontinuities largely to nonspecific interactions between proteins and the SFM probe.
• Identified that the cantilever-spherical bead system can lead to false separation distance indications.
• Noted that lateral interactions and "stick and slip" phenomena are influenced by protein heterogeneity and limited molecular mobility, especially with increased contact time.

Conclusions:

• Nonspecific interactions can mimic specific bond breaking in SFM measurements.
• The mechanical setup of the SFM probe can influence distance measurements.
• Careful consideration of protein properties and experimental conditions is necessary to avoid misinterpreting SFM adhesion data.