DYNEIN ARMS ARE OSCILLATING FORCE GENERATORS

Eukaryotic flagella beat rhythmically(1). Dynein is a protein that pow ers flagellar motion, and oscillation may be inherent to this protein( 2-5). Here we determine whether oscillation is a property of dynein ar ms themselves or whether oscillation requires an intact axoneme(6), wh ich is the central core of the flagellum and consists of a regular arr ay of microtubules. Using optical trapping nanometry(7,8), we measured the force generated by a few dynein arms on an isolated doublet micro tubule, When the dynein arms on the doublet microtubule contact a sing let microtubule and are activated by photolysis of caged ATP(8), they generate a peak force of similar to 6 pN and move the singlet microtub ule over the doublet microtubule in a processive manner. The force and displacement oscillate with a peak-to-peak force and amplitude of sim ilar to 2 pN and similar to 30 nm, respectively. The geometry of the i nteraction indicates that very few (possibly one) dynein arms are need ed to generate the oscillation. The maximum frequency of the oscillati on at 0.75 mM ATP is similar to 70 Hz; this frequency decreases as the ATP concentration decreases. A similar oscillatory force is also gene rated by inner dynein arms alone on doublet microtubules that are depl eted of outer dynein arms. The oscillation of the dynein arm may be a basic mechanism underlying flagellar beating.