Unique transmembrane domain interactions differentially modulate integrin αvβ3 and αIIbβ3 function

Area of Science:

• Membrane protein biophysics
• Molecular cell biology
• Structural biology

Background:

• Transmembrane (TM) helix-helix interactions are vital for cell-surface receptor assembly and signaling.
• Single-span membrane proteins often possess conserved TM motifs for interaction, but dual-engagement mechanisms are sparsely evidenced.
• Integrin receptors, crucial for cell adhesion and signaling, rely on TM domain interactions for their function.

Purpose of the Study:

• To investigate the functional roles of two conserved interaction motifs within the integrin β3-subunit's TM domain.
• To elucidate how these motifs mediate distinct α-subunit interactions and influence integrin signaling.
• To explore the mechanism of dual-engagement in integrin TM domains.

Main Methods:

• Site-directed mutagenesis to alter specific amino acid residues in the β3 TM domain.
• Optical trap-based force spectroscopy to measure protein interactions.
• Molecular modeling to simulate and visualize TM helix interactions.

Main Results:

• The first motif, characterized by "large-large-small" packing, mediates β3-αIIb TM interactions, maintaining integrin αIIbβ3 in an inactive state.
• The second motif, S-x3-A-x3-I, mediates β3 TM interactions with the αv TM subunit, forming integrin αvβ3.
• Disruption of the β3 S-x3-A-x3-I motif by mutation activates αvβ3, inducing binding to osteopontin and the WOW-1 antibody.

Conclusions:

• The integrin β3 TM domain utilizes two mutually exclusive interaction motifs.
• These motifs enable alternate α-subunit pairing, leading to the formation of distinct integrin complexes (αIIbβ3 and αvβ3).
• This dual-engagement mechanism allows for the generation of integrins with different biological functions and signaling outputs.