Translocation of microtubules caused by the αβ, β and γ outer arm dynein subparticles of Chlamydomonas

Abstract

Three kinds of subparticles of Chlamydomonas outer-arm dynein containing the alphabeta, beta and gamma heavy chains were isolated and assayed for their activities to translocate microtubules in vitro. All of them had activities to form bundles of microtubules in solution in an ATP-dependent manner and, when adsorbed on an appropriate glass surface, translocated microtubules. The alphabeta subparticle readily translocated microtubules on a silicone-coated glass surface with a velocity of 4.6 micron/second at 1 mM ATP. The beta subparticle translocated microtubules after it had been preincubated with tubulin dimer and when the Brownian movement of microtubules was suppressed by addition of methylcellulose. The velocity was on average 0.7 micron/second. The gamma subparticle translocated microtubules after being preincubated with tubulin dimer and adsorbed onto a silicone-coated glass surface. The velocity was about 3.8 micron/second. The tubulin dimer appeared to facilitate in vitro motility by blocking the ATP-insensitive binding of dynein subparticles to microtubule. The alphabeta, beta and gamma subparticles were thus found to have different properties as motor proteins. In addition, these subparticles showed different dependencies upon the potassium acetate concentration. Hence the outer-arm dynein of Chlamydomonas is a complex of motor proteins with different properties.