Chemistry Reference
In-Depth Information
3
Imaging and Molecular Motors
Yale E. Goldman
3.1
Introduction
Molecular motors, the enzymes that power cellular motions and determine cell
shape, have long been productive subjects for development of new techniques in
biophysics research [1, 2]. Many of the techniques described in this topic, examining
forces, localization and structure of singlemolecules were rst described in studies of
molecular motors. For instance, one of the early reports of detection of single
fluorescent molecules was made by T. Yanagida and his colleagues using myosin
and a fluorescent analog of ATP binding to its active site [3]. The first biological
application of infrared optical traps by Block, Berg, and their colleagues was for
studies of the bacterial flagellar rotary motor [4]. Consequently, our understanding of
these cellular nano-machines has beenmarkedly accelerated by the development and
availability of single-molecule mechanical and imaging methods.
There are several reasons for the synergy between these techniques and the
molecular motor field. Firstly, the primary functional outputs of active molecular
motors are forces and displacements, signals particularly amenable to detection
using optical traps, scanning probes, and fluorescence microscopy. The forces,
motions and dynamics are all within ranges accessible using the single-molecule
techniques summarized in this topic. Transduction of metabolic energy into me-
chanical work is accomplished in molecular motors by internal structural changes,
such as rotational motions and sliding, that are particularly large and detectable.
Conversely, the output of molecular motors, such as local positions, spatial orienta-
tions and fluctuations, are obscure in isotropic suspensions. Many of the motor
systems operate virtually on their own, making it dif cult for them to be synchro-
nized for ensemble studies. Motor research thus needs single-molecule techniques,
and single-molecule biophysics has bene ted from progress on molecular motors.
In this chapter, single molecule fluorescence imaging techniques that have been
applied to the three classical molecular motors, myosin, kinesin and dynein, are
described and the information garnered is brie y summarized. Reconstitution of
 
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