Fig 4. Model of the severing, capping, uncapping and inactivation/release cycle of gelsolin.

The cartoon presents a model for the cycle of activation and function of gelsolin. Severing and capping: Elevated free calcium levels activate gelsolin, releasing ATP, leading to severing and capping of actin filaments. Depolymerization: Gelsolin-capped filaments will depolymerize from their pointed ends. Uncapping and polymerization: Gelsolin-capped actin filaments will be uncapped on encountering PIP₂ in the membrane, resulting in force being exerted on the membrane from the polymerization of the uncapped filaments. Inactivation and membrane release: Gelsolin will be released from PIP₂ and the membrane by competition with ATP. Following its release gelsolin is able to undergo subsequent cycles of severing, capping, uncapping and inactivation/release.