National Institute of Advanced Industrial Science and Technology (AIST) and Kanazawa University Kien Xuan Ngo, Noriyuki Kodera Taro Q.P. Uyeda
AFM images of actin filaments have double-helical appearance, with alternating bright and dark patterns. The bright areas are the tall parts of the filament, where the two protofilaments align vertically (peaks). Cofilin binds cooperatively to actin filaments, forming clusters. Those cofilin clusters are identified in AFM images as brighter peaks, due to thickening of the filament, and shorter helical pitch (distance between the peaks) representing “supertwisting”. Cofilin clusters grow unidirectionally toward the pointed end of the filament. White arrowheads show growth of the cofilin cluster, and yellow and magenta arrowheads show binding of S1. Magenta arrowheads indicate S1 molecules whose binding angle could not be determined, either for geometric reasons (i.e., binding on the upper face of the filament) or because the binding was too short-lived. Cofilin clusters grew unidirectionally to the pointed end direction in the presence of ADP only or ADP+Pi, indicating that this is independent on the gradient of chemical states of actin subunits along the length. For details, please see the original paper linked below. Conditions: F buffer containing 1 mM ADP, 0.1 mM ATP, 20 nM S1, and 75 nM cofilin. Imaged at 2 frames/s and played at 5 frames/s. The width of the imaged field: 280 nm, Z-scale: 0–12 nm.
(2015.06.18)