Single molecule characterization of P-selectin/ligand binding

Area of Science:

• Biophysics
• Cellular Adhesion
• Molecular Interactions

Background:

• P-selectin mediates cell adhesion in inflammation and metastasis.
• The relationship between single receptor-ligand affinity and overall cell avidity is unclear.
• Understanding these interactions is crucial for inflammation and metastasis research.

Purpose of the Study:

• To measure the tensile strength and off-rate of single P-selectin interactions with ligands on human polymorphonuclear leukocytes (PMNs) and colon carcinomas.
• To compare the single molecule binding properties with the overall cell avidity.
• To provide a mechanistic basis for differential cell rolling on P-selectin substrates.

Main Methods:

• Single molecule force spectroscopy was used to probe P-selectin binding to intact human PMNs and LS174T colon carcinoma cells.
• Measurements included tensile strength and unstressed off-rate of individual receptor-ligand bonds.
• Monte Carlo simulations were employed to model bond rupture dynamics.

Main Results:

• P-selectin/PSGL-1 interaction on PMNs showed high tensile strength (up to 175 pN) and a low off-rate (0.20 s⁻¹).
• P-selectin binding to a novel colon carcinoma ligand exhibited lower tensile strength (~125 pN) and a higher off-rate (2.78 s⁻¹).
• Simulation data aligned with experimental findings, supporting the measured affinity differences.

Conclusions:

• Significant differences in P-selectin/ligand binding affinity exist between PMNs and colon carcinomas.
• These affinity variations provide a mechanism for the distinct rolling behaviors of these cells on P-selectin substrates.
• Single molecule affinity measurements are essential for understanding cell adhesion under flow.