Attractive and repulsive interactions between and within adsorbed ribonuclease A layers

Area of Science:

• Biophysics
• Surface Science
• Protein Adsorption

Background:

• Understanding protein adsorption is crucial for biomaterials and biosensors.
• The interaction of adsorbed protein layers with surfaces and each other is complex.
• Pancreatic ribonuclease A (RNase A) is a model protein for studying adsorption phenomena.

Purpose of the Study:

• To investigate the interaction forces between adsorbed pancreatic RNase A layers on mica.
• To analyze the kinetics and equilibrium behavior of RNase A adsorption under varying conditions.
• To validate a discrete lattice model for predicting protein adsorption behavior.

Main Methods:

• Surface force-distance measurements using atomic force microscopy.
• Analysis of adsorbed protein layer kinetics and equilibrium.
• Varying ionic strength and pH of aqueous solutions.
• Refractive index measurements to determine adsorbed protein concentration.

Main Results:

• Adsorbed RNase A layers initially attract mica but become repulsive over time.
• Protein layer compression and increased concentration observed during surface approach.
• Ionic strength and pH significantly alter inter-protein interactions and layer structure.
• Kinetics show characteristic length scales varying linearly with the square root of time, indicating diffusion control.

Conclusions:

• The behavior of adsorbed RNase A layers can be predicted by a discrete lattice model.
• Electrostatic and hydrophobic interactions play key roles in protein layer behavior.
• Adsorption kinetics are diffusion-driven, with layer thickness and jump-in distance dependent on time.
• Contaminants may influence observed long-range repulsive forces at specific pH values.