Fig. 4.
Summary of single-molecule kinetics in the dendritic actin network. The numbers in bold letters show kinetic parameters obtained in fluorescence single-molecule studies.3)–5) Overall, dynamics at the barbed end has turned out to be faster than previously thought. The dissociation of capping protein occurs at 0.58 s−1. Fast elongation of the free barbed end is derived from the speed of mDia1-catalyzed processive actin elongation in lamellipodia. In contrast, the pointed end side of F-actin, where Arp2/3 complex associates, disassembles much slower at the rate of 0.048 s−1. Certain mechanisms other than simple treadmilling must compensate the imbalance between fast growing barbed ends with slowly disassembling pointed ends. AIP1-mediated actin severing/disruption might be one of the mechanisms. It turned out to be ≈15 times more frequent than F-actin nucleation by Arp2/3 complex.