Assembly of Cytoskeletal Filaments

The cytoskeleton comprises three types of protein filaments — microfilaments, microtubules, and intermediate filaments. These filaments assemble and disassemble according to the cell’s requirements.

Each type of filament is made up of smaller subunits that self-associate through end-to-end protein contacts and are held together by weak associations like non-covalent interactions and hydrophobic forces.

With the help of actin-binding proteins, microfilaments assemble either into bundles of individual filaments crosslinked into parallel arrays, or, as complex three-dimensional networks.

Microtubules consist of tubulin heterodimers that assemble end-to-end to form a hollow cylinder made up of thirteen protofilaments. Microtubule-associated proteins or MAPs help the protofilaments polymerize and stabilize the assembled structure.

Intermediate filaments are composed of elongated fibrous proteins that vary across cell types. These protein subunits form tetramers through a multistep process. Finally, the tetramers associate to form a rigid rope-like structure.