Torsional Brownian Motion of Single Actin Filamants




To estimate the torsional ridigity of an actin filament, single actin filaments were attached to polystyrene beads on a glass surface to form 'actin bridges.'  To the middle of a straight actin filament, a bead duplex was attached with the aid of optical tweezers.  After the optical trap was turned off, the bead duplex oscillated around the filament, reflecting the torsional Brownian motion of the single actin filament.  In the movies, the left panel shows transmitted images of the beads and the right panel shows fluorescence images of the actin filament (and beads).  (The magnification of the fluorescence images is one half that of the transmitted images.)  To our surprize, actin filaments binding Mg2+ were thres times more flexible than actin filaments binding Ca2+.  
                                                                                 Yasuda, R et al.  J. Mol. Biol. 263, 227-236 (1996).