ADF/cofilin weakens lateral contacts in the actin filament

Observed in vivo motility rates can only be accounted for if the rate of ac tin filament treadmilling in cells is considerably greater than has been qu antified for purified actin in vitro. ADF/cofilin is uniquely suited to pro mote actin dynamics in cells, owing to its remarkable ability to change act in filament structure. In earlier work we showed that human cofilin chanRge s filament twist by about 5 degrees per subunit and suggested that this con tributes to increased filament turnover. Our initial structural modeling pr ovided some insights into how the longitudinal actin-actin contacts might b e disrupted following cofilin-induced twisting. Here we present direct evid ence that cofilin also disrupts lateral actin-actin contacts in the filamen t and suggest a model showing how this could contribute to cofilin's novel effects on actin filament dynamics and assembly. (C) 1999 Academic Press.