Activation of the integrin alpha v beta 3 involves a discrete cation-binding site that regulates conformation

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Integrin activation drives leukocyte and platelet adhesion.
• Integrin alpha v beta 3 shares a beta subunit with the known activable platelet integrin alpha IIb beta 3.
• Conformational changes in alpha v beta 3 may subtly regulate constitutively adhered cells.

Purpose of the Study:

• To investigate if integrin alpha v beta 3 undergoes activation-like conformational changes.
• To explore the role of calcium and ligand binding in alpha v beta 3 modulation.
• To characterize the functional differences between basal and activated alpha v beta 3 states.

Main Methods:

• Utilized M21 human melanoma cells expressing alpha v beta 3.
• Employed a monoclonal antibody (AP5) targeting the beta 3 subunit for activation studies.
• Analyzed ligand binding, migration, and cation-binding site interactions.

Main Results:

• Alpha v beta 3 exhibits conformational changes upon ligand analog binding and antibody activation.
• A shared cation-binding site with an apparent calcium Kd of ~20 microM was identified.
• Physiological calcium levels (~40%) stabilize a conformation detected by AP5.
• Two distinct conformational states (calcium-bound/basal vs. AP5/ligand-bound/activated) were proposed.

Conclusions:

• Integrin alpha v beta 3 can exist in at least two functional states: basal (calcium-stabilized, tight adhesion) and activated (AP5/ligand-stabilized, migration-conducive).
• AP5 antibody activates alpha v beta 3 by blocking calcium binding to a shared cation site.
• These findings reveal a mechanism for regulating alpha v beta 3 function in cell adhesion and migration.