Twirling Behavior of Unconventional and Recombinant Myosins
John H. Lewis, John F. Beausang, W. Harry (Trey) Schroeder (University of Pennsylvania), Kazu Homma, Mitsuo Ikebe (University of Massachusetts), Yale E. Goldman (University of Pennsylvania)
Using single molecule fluorescence polarization, we measure the helical path actin follows as it is translocated axially by various isoforms and fragments of myosin. The azimuthal angle, a, of a single fluorescent probe within the actin often shows steady change as above, indicating a clear helical (‘twirling’) motion.
The pitch of this twirling relates to the helical nature of actin, any torque exerted by the motor, and the allowed target landing sites on actin. Twirling can be left-handed (native myosin II, myosin V, and recombinant myosin V with 6 calmodulins bound to 6 calmodulain binding (IQ) motifs (the normal complement)). Or twirling can be left-handed (myosin VI), or ambidextrous (recombinant myosin V with 4 IQ motifs). These results show how the size and flexibility of these myosins direct their transport properties and ability to negotiate around obstacles.