Direct observation of processive movement by individual myosin V molecules

Myosin V is an unconventional myosin thought to move processively along actin filaments. To have hard evidence for the high processivity, we sought to observe directly the movement by individual native chick brain myosin V (BMV) molecules with fluorescent calmodulin, Single BMV molecules did exhibit highly processive movement along actin filaments fixed to a coverslip. BMV continued to move up to the barbed end of its actin track, and did not readily detach from action, The barbed end, therefore, got brighter with time, because of a constant stream of BMV traffic, The maximum speed of the processive movement was 1 mu m/s, and the maximum actin-activated ATPase rate was 2.4 s(-1). These values apparently imply that BMV travels a great distance, 400 nm, per an ATPase cycle. (C) 2000 Academic Press.