Structural mechanism for bidirectional actin cross-linking by T-plastin

Area of Science:

• Cell Biology
• Structural Biology
• Biochemistry

Background:

• Cytoskeletal networks, crucial for cell mechanics and motility, are organized by cross-linking proteins.
• Plastins/fimbrins are ancient proteins that build diverse actin networks essential for cellular processes.
• The precise structural mechanisms of these interfilament linkages are not fully understood.

Purpose of the Study:

• To elucidate the structural basis of actin network assembly by human T-plastin.
• To understand how T-plastin's cross-linking mechanism influences actin network architecture and function.
• To investigate the role of T-plastin in maintaining cellular protrusions.

Main Methods:

• Utilized a machine-learning-enhanced cryo-electron microscopy pipeline.
• Visualized cross-linkers bridging multiple actin filaments.
• Performed structural, biochemical, and cell biological analyses.

Main Results:

• Discovered a sequential bundling mechanism by which T-plastin bridges actin filaments in parallel and antiparallel orientations.
• Identified distinct structural landscapes adopted by T-plastin in different bridging orientations.
• Demonstrated that these distinct structures are compatible with actin networks of divergent architectures and functions.
• Highlighted the role of inter-CHD linkers in flexible yet stable cross-linking.

Conclusions:

• T-plastin's sequential bundling mechanism is key to forming diverse actin networks with specific functions.
• The structural plasticity of T-plastin allows it to adapt to different actin network architectures.
• Disruptions in T-plastin cross-linking may contribute to hereditary bone diseases.