Power Law Behavior in Protein Desorption Kinetics Originating from Sequential Binding and Unbinding

Area of Science:

• Biomaterials Science
• Surface Chemistry
• Single-Molecule Biophysics

Background:

• Protein adsorption is crucial for biomaterial function and biocompatibility.
• Previous studies indicated reversible protein adsorption with long residence times, often attributed to distinct binding sites.
• The underlying mechanism for these long residence times remained unclear.

Purpose of the Study:

• To propose and validate a new model for protein adsorption dynamics at the single-molecule level.
• To explain the origin of long-tailed residence time distributions in protein adsorption.
• To investigate the role of sequential binding events in protein-surface interactions.

Main Methods:

• Development of a theoretical model describing protein adsorption as a series of reversible, sequential steps ('zippering').
• Mathematical analysis of the residence time distribution, predicting a transition from exponential to power-law behavior.
• Experimental single-molecule imaging of fluorescently labeled fibrinogen adsorption onto glass surfaces.

Main Results:

• The proposed 'zippering' model accurately predicts the observed residence time distributions.
• The model demonstrates that long residence times can arise from multiple sequential adsorption steps.
• Experimental data for fibrinogen adsorption fit the model, supporting the stepwise adsorption hypothesis.

Conclusions:

• Long protein residence times on surfaces are explained by sequential, reversible binding events, not solely by rare, strong adsorption sites.
• The 'zippering' model provides a framework for understanding and predicting protein adsorption dynamics.
• Findings offer guidance for controlling protein adsorption on biomaterials for improved performance.