Dynein arms are oscillating force generators

Abstract

Eukaryotic flagella beat rhythmically. Dynein is a protein that powers flagellar motion, and oscillation may be inherent to this protein. Here we determine whether oscillation is a property of dynein arms themselves or whether oscillation requires an intact axoneme, which is the central core of the flagellum and consists of a regular array of microtubules. Using optical trapping nanometry, we measured the force generated by a few dynein arms on an isolated doublet microtubule. When the dynein arms on the doublet microtubule contact a singlet microtubule and are activated by photolysis of caged ATP8, they generate a peak force of approximately 6pN and move the singlet microtubule over the doublet microtubule in a processive manner. The force and displacement oscillate with a peak-to-peak force and amplitude of approximately 2 pN and approximately 30 nm, respectively. The geometry of the interaction indicates that very few (possibly one) dynein arms are needed to generate the oscillation. The maximum frequency of the oscillation at 0.75 mM ATP is approximately 70 Hz; this frequency decreases as the ATP concentration decreases. A similar oscillatory force is also generated by inner dynein arms alone on doublet microtubules that are depleted of outer dynein arms. The oscillation of the dynein arm may be a basic mechanism underlying flagellar beating.

Thinking about flagellar oscillation

“…The existence of a reverse mode might be particularly valuable in very long flagella, as it would prevent the accumulation of twist that might be expected if there is only an ON mode in the forward direction [Hines and Blum, 1985]. However, a clearer suggestion for a reverse mode of dynein operation, rather than an OFF mode, is provided by the observations of Shingyoji et al [1998]. Oscillatory sliding, with amplitudes in excess of 50 nm, appeared to be produced by one, or a few, dynein motors.…”

The radial spokes and central apparatus: Mechano‐chemical transducers that regulate flagellar motility

“…In a recent publication, Lindemann proposes that the radial spokes and central apparatus play a role in redistributing this transverse force during the switching event, and that movable attachments between the radial spokes and central pair projections are required for mediating the transmission of this force [Lindemann, 2003]. Testing the prediction that strain in the radial spoke stalk locally modulates dynein activity will most likely require the development of a new in vitro assay combined with micromanipulation technology [for example, see Shingyoji et al, 1998]. …”

A rotary molecular motor that can work at near 100% efficiency

“…Linear motors produce movement along a ¢lamentous structure; for example, myosin along an actin ¢lament (Goldman 1998;Suzuki et al 1998;Dominguez et al 1998;Kitamura et al 1999), kinesin Lohman et al 1998;Mandelkow & Johnson 1998) and dynein (Shingyoji et al 1998) along a microtubule, and RNA polymerase along DNA . Known linear motors are driven by free energy obtained from nucleotide hydrolysis.…”