7 - Composition and Assembly of Axonemal Dyneins

Abstract

This chapter focuses on the composition and structure of axonemal dyneins. Axonemal dyneins form the inner and outer arms that are associated—with doublet microtubules within cilia and flagella. Axonemal dyneins come in multiple forms that contain one, two, or three non-identical heavy chains (depending upon the organism and location in the cilium). Each heavy chain has a globular motor domain with a doughnut-shaped structure believed to resemble that of other AAA proteins, a coiled coil “stalk” that binds to the microtubule, and an extended tail (or “stem”) that attaches to a neighboring microtubule of the same axoneme. Axonemal dyneins can be classified based on whether they contain either a single or multiple motor units. The classes of dynein components are explained in the chapter, which also describes monomeric inner dynein arms, dimeric inner dynein arms, outer dynein arms, and inter dynein linkers. Furthermore, it describes the properties and organization of axonemal dynein motor units. Genetic and biochemical studies in a variety of model organisms have revealed the enormously complex nature of axonemal dyneins. Although most of the core dynein components have now been identified, there still remain challenges, especially as regards defining inner arms that are present in very low amounts and in identifying proteins that only transiently interact with the in situ arms.