Treadmilling

The cytoskeleton is a highly dynamic part of a cell and cytoskeletal filaments constantly grow and shrink through addition and removal of subunits.

[6] Cofilin functions by binding to ADP-actin on the negative end of the filament, destabilizing it, and inducing depolymerization.

[6] What determines whether the ends grow or shrink is entirely dependent on the cytosolic concentration of available monomer subunits in the surrounding area.

The cell attempts to maintain a subunit concentration between the dissociation constants at the plus and minus ends of the polymer.

Microtubules formed from pure tubulin undergo subunit uptake and loss at ends by both random exchange diffusion, and by a directional (treadmilling) element.

Single filaments and/or patches have been demonstrated to treadmill in vitro[15][16] and inside bacterial cells.

[17][18] A Monte Carlo model of FtsZ treadmilling has been designed, based on a conformational change of subunits upon polymerization and GTP hydrolysis.

Actin Treadmilling Mechanism. This figure assumes that the critical concentration at the positive end is less than the critical concentration at the negative end and that the cytosolic subunit concentration is in between the positive and negative end critical concentrations.