Abstract
In eukaryotic cilia and flagella, various types of axonemal dyneins orchestrate their distinct functions to generate oscillatory bending of axonemes. The force-generating mechanism of dyneins has recently been well elucidated, mainly in cytoplasmic dyneins, thanks to progress in single-molecule measurements, X-ray crystallography, and advanced electron microscopy. These techniques have shed light on several important questions concerning what conformational changes accompany ATP hydrolysis and whether multiple motor domains are coordinated in the movements of dynein. However, due to the lack of a proper expression system for axonemal dyneins, no atomic coordinates of the entire motor domain of axonemal dynein have been reported. Therefore, a substantial amount of knowledge on the molecular architecture of axonemal dynein has been derived from electron microscopic observations on dynein arms in axonemes or on isolated axonemal dynein molecules. This review describes our current knowledge and perspectives of the force-generating mechanism of axonemal dyneins in solo and in ensemble.
Highlights
Orchestrated activities of axonemal dyneins and their interactions with microtubules drive ciliary and flagellar movement
The axonemal dynein is the major component of the dynein arms [2]
In a cross section of the electron micrographs of the axoneme, the dynein arms were observed as two rows of protrusions extending from one side of each doublet microtubule in the axonemes [3]
Summary
Orchestrated activities of axonemal dyneins and their interactions with microtubules drive ciliary and flagellar movement. The other inner arm dyneins, termed subspecies a, b, c, d, e, and g, consist of monomeric heavy and light chains (actin and centrin/p28) [12,13,14] These heavy chains of axonemal dyneins so far studied have distinct motile properties in vitro [12,15,16,17,18,19] and specific functions in situ in flagellar motility [20,21]. By contrast to the switching of the active sides, the bend propagation toward the tip of the axoneme seems to be the sequential process activating dynein arms [30,31,32,33] To understand these coordination mechanisms of axonemal dyneins during ciliary and flagellar beating is one of the ultimate aims for the research on the motility of cilia and flagella. We summarize studies mainly on axonemal dyneins, their force generating mechanisms, and their roles in an axonemal structure
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