Competitive displacement of cofilin can promote actin filament severing.

Highlights: [•] Myosin and phalloidin are predicted to modulate cofilin-mediated filament severing. [•] Competitive displacement of bound cofilin by myosin and phalloidin is measured. [•] Competition can promote filament severing, depending on initial cofilin occupancy. [•] Maximal severing occurs near half cofilin occupancy, even with competitors present. [•] We propose a general “severodyne” framework to describe cofilin regulation. [Copyright &y& Elsevier]