Biochemical and structural bases for talin ABSs-F-actin interactions.

Area of Science:

• Cell Biology
• Biochemistry
• Structural Biology

Background:

• Focal adhesions (FAs) are crucial for cell polarization and migration.
• Talin acts as a key linker between integrin receptors and the actin cytoskeleton within FAs.
• Talin possesses three actin-binding sites (ABS1-3) involved in FA initiation and maturation.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying the interactions between talin's actin-binding sites (ABSs) and filamentous actin (F-actin).
• To understand the multivalent binding behavior of talin to F-actin.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structure of the F-actin-ABS3 complex at 2.9 Å resolution.
• Analysis of the structural interactions between talin subdomains and F-actin.

Main Results:

• ABS3 binds to two actin monomers, with its R13 rod subdomain and DD domain interacting with actin.
• ABS3 dimerization via the DD domain on the actin surface is essential for F-actin engagement.
• Binding to F-actin causes distortion of the R13 helical bundle, releasing the H1 helix, a mechanism also seen in other tension-sensing proteins.
• ABS2 exhibits multiple F-actin binding regions, suggesting a role in strengthening interactions during FA maturation.

Conclusions:

• The structural insights reveal how talin's ABSs interact with F-actin, explaining its role in FA dynamics.
• The observed unfolding of talin's R13 domain upon F-actin binding suggests a force-sensing mechanism.
• Talin's multivalent binding to F-actin, particularly through ABS2, contributes to the stability and maturation of focal adhesions.