Reconstituted nascent adhesion condensates drive actin polymerization on supported lipid bilayers

Area of Science:

• Cell Biology
• Biophysics
• Biochemistry

Background:

• Nascent adhesions are crucial integrin-based assemblies linking the extracellular matrix to the actin cytoskeleton.
• These early adhesions mature into focal adhesions, a process potentially involving liquid-like organization of proteins due to weak, multivalent interactions.
• The precise role of phase separation in shaping actin polymerization and organization within nascent adhesions remains largely unexplored.

Purpose of the Study:

• To investigate how the identity of vasodilator-stimulated phosphoprotein (VASP)-recruiting adaptor proteins, specifically zyxin and vinculin, influences the properties of protein condensates.
• To determine how these differential condensate properties affect actin coupling and polymerization dynamics.
• To elucidate the mechanism by which adaptor proteins modulate nascent adhesion maturation into focal adhesions.

Main Methods:

• Comparative analysis of zyxin-VASP and vinculin-VASP assemblies in vitro and/or in cellular models.
• Characterization of condensate properties such as fluidity, rigidity, and dynamics using biophysical techniques.
• Assessment of integrin clustering and actin filament growth in response to these assemblies.

Main Results:

• Both zyxin-VASP and vinculin-VASP assemblies effectively promote integrin clustering and support actin filament growth.
• Zyxin-VASP condensates exhibit fluid-like behavior, redistributing along newly formed actin bundles.
• Vinculin-VASP condensates are more rigid, failing to spread along actin despite supporting polymerization.

Conclusions:

• Differential recruitment of VASP adaptors (zyxin vs. vinculin) significantly modulates the biophysical properties of protein condensates.
• These distinct condensate properties directly impact actin architecture and dynamics.
• This provides a mechanistic insight into how variations in adaptor protein identity can regulate the maturation process from nascent adhesions to focal adhesions.