Fluorescence tracking of motor proteins in vitro

Motor proteins convert the chemical energy of adenosine triphosphate (ATP) hydrolysis into directed movement along filamentous tracks, such as DNA, microtubule, and actin. The motile properties of motors are essential to their wide variety of cellular functions, including cargo transport, mitosis, cell motility, nuclear positioning, and ciliogenesis. Detailed understanding of the biophysical mechanisms of motor motility is therefore essential to understanding the physical basis of these processes. In which direction is the motor going? How fast and how far can a single motor walk down its track? How is ATP hydrolysis coupled to directed motion? How do multiple subunits of a motor coordinate with each other during motility? These questions can be addressed directly by tracking motors at a single-molecule level. This chapter will focus on high-resolution fluorescence tracking techniques of the processive cytoskeletal motors: myosins, kinesins, and cytoplasmic dynein. We outline the theoretical and practical considerations for studying these motors in vitro using fluorescence tracking at nanometer precision.