All-atom simulations reveal distinct pathways for α_IIbβ₃ activation by biochemical vs. mechanical cues

Area of Science:

• Biochemistry and Biophysics
• Molecular Biology
• Cellular Mechanics

Background:

• Platelet aggregation, essential for hemostasis and thrombosis, is regulated by α_IIbβ₃ integrin conformational activation.
• Both extracellular arginine-glycine-aspartic acid (RGD) ligands and mechanical forces can trigger this activation, but the precise mechanisms remain elusive.

Purpose of the Study:

• To elucidate the distinct molecular mechanisms by which mechanical force and RGD binding induce conformational changes in α_IIbβ₃ integrin.

Main Methods:

• Utilized all-atom molecular dynamics simulations to investigate the structural dynamics of α_IIbβ₃ integrin under different activation stimuli.

Main Results:

• Mechanical force applied to the RGD-binding site induced long-range, correlated motions, facilitating head-leg separation.
• RGD binding increased localized, non-correlated fluctuations, weakening leg coordination without generating long-range motions.
• Both mechanical force and RGD binding were shown to stabilize the open, extended conformation of α_IIbβ₃ integrin.

Conclusions:

• Mechanical and biochemical stimuli play complementary yet distinct roles in integrin conformational activation.
• A balance between global coordination and local fluctuations governs integrin activation, with distinct pathways emerging based on the dominant cue.