Distinct binding kinetics of E-, P- and L-selectins to CD44

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Mechanics

Background:

• Molecular-level interactions between selectins and cluster of differentiation 44 (CD44) are complex due to CD44 glycosylation and isoform diversity.
• Understanding these interactions is vital for elucidating cellular adhesion mechanisms in various physiological and pathological processes.

Purpose of the Study:

• To quantify the binding kinetics of three selectin members (E-, P-, and L-selectins) with recombinant CD44.
• To explore the microstructural mechanisms underlying these selectin-CD44 interactions.
• To elucidate the functional differences between selectin-CD44 interactions.

Main Methods:

• Experimental measurements of binding kinetics under shear flow.
• Molecular docking simulations to predict binding epitopes.
• Molecular dynamics (MD) simulations (equilibration and steered) to analyze binding free energy, rupture force, and lifetime.

Main Results:

• E-selectin-CD44 interactions mediated firm adhesion with the strongest rupture force.
• P- and L-selectins exhibited different association/dissociation rates, mediating stable rolling and transient adhesions, respectively.
• MD simulations supported experimental findings, predicting binding epitopes on selectin side faces and correlating binding energy, rupture force, and lifetime with observed adhesion types.

Conclusions:

• The study provides quantitative data on selectin-CD44 binding kinetics and mechanisms.
• Distinct biophysical properties of E-, P-, and L-selectin interactions with CD44 explain their differential roles in cell adhesion.
• These findings offer fundamental insights into the functional diversity of selectin-CD44 interactions.