ADF/cofilin weakens lateral contacts in the actin filament.

Observed in vivo motility rates can only be accounted for if the rate of actin filament treadmilling in cells is considerably greater than has been quantified for purified actin in vitro. ADF/cofilin is uniquely suited to promote actin dynamics in cells, owing to its remarkable ability to change actin filament structure. In earlier work we showed that human cofilin chanRges filament twist by about 5 degrees per subunit and suggested that this contributes to increased filament turnover. Our initial structural modeling provided some insights into how the longitudinal actin-actin contacts might be disrupted following cofilin-induced twisting. Here we present direct evidence that cofilin also disrupts lateral actin-actin contacts in the filament and suggest a model showing how this could contribute to cofilin's novel effects on actin filament dynamics and assembly.