Substructure of the outer dynein arm

Abstract

The substructure of the outer dynein arm has been analyzed in quick-frozen deep-etch replicas of Tetrahymena themophila and Chlamydomonas reinhardi axonemes. Each arm is composed of 5 morphologically discrete components: an elliptical head; 2 spherical feet; a slender stalk; and an interdynein linker. The feet make contact with the A microtubule of each doublet; the stalk contacts the B microtubule; the head lies between the feet and stalk; and the linker associates each arm with its neighbor. The spatial relationships between these 5 components are distinctly different in rigor (ATP-depleted) vs. relaxed (ATP- or vanadate plus ATP-treated) axonemes, and the stalk appears to alter its affinity for the B microtubule in the relaxed state. Images of living cilia attached to Tetrahymena cells show that the relaxed configuration is adopted in vivo. These observations are related to morphological and experimental studies reported by others. Several models that suggest how this newly described dynein morphology may relate to dynein function are proposed.