Chapter 3 - Force-Generating Mechanisms of Dynein Revealed through Single Molecule Studies

Abstract

This chapter describes the current knowledge of the force-generating mechanism of dynein, with emphasis on research findings from electron microscopy and single molecule nanometry. In recent decades, the development of a number of single molecule technologies such as atomic-force microscopy, optical-trap nanometry, and fluorescence microscopy have provided tools for studying the dynamics of single molecules in situ over timescales from milliseconds to seconds. The single molecule sensitivities of these methods permit studies to be made on conformational changes, motility, mechanical properties, and functions of protein motors that are masked in ensemble-averaged experiments. Processivity, step size, and dwell time distributions are among the properties that can be directly measured by single molecule techniques. Furthermore, electron microscopic observations and single molecule measurements have shed light on several key unsolved questions concerning how the dynein molecule is organized, what conformational changes in the molecule accompany ATP hydrolysis, and whether two or three motor domains are coordinated in the movements of dynein. Mechanical experiments at the single molecule level raise questions such as whether dynein molecules are really organized into intact configurations on artificial substrates and how the dimer or the trimer coordinates its multiple motor domains during stepping. In studies of axonemal dyneins, three layers of coordination are considered: intra-domain coordination within a heavy chain, intramolecular coordination among multiple motor domains within each arm, and intermolecular coordination among multiple dynein arm complexes. The chapter summarizes recent research on axonemal dyneins and the findings on the mechanics, biochemistry, motility, and force generated by dyneins in axonemes of cilia and flagella.