Systematic Comparison of in Vitro Motile Properties between Chlamydomonas Wild-type and Mutant Outer Arm Dyneins Each Lacking One of the Three Heavy Chains*

Outer arm dynein (OAD) of cilia and flagella contains two or three distinct heavy chains, each having a motor function. To elucidate their functional difference, we compared the in vitro motile properties of Chlamydomonas wild-type OAD containing the α, β, and γ heavy chains and three kinds of mutant OADs, each lacking one of the three heavy chains. For systematic comparison, a method was developed to introduce a biotin tag into a subunit, LC2, which served as the specific anchoring site on an avidin-coated glass surface. Wild-type OAD displayed microtubule gliding in the presence of ATP and ADP, with a maximal velocity of 5.0 μm/s, which is approximately 1/4 of the microtubule sliding velocity in the axoneme. The duty ratio was estimated to be as low as 0.08. The absence of the β heavy chain lowered both the gliding velocity and ATPase activity, whereas the absence of the γ heavy chain increased both activities. Strikingly, the absence of the α heavy chain lowered the gliding velocity but increased the ATPase activity. Thus, the three heavy chains are likely to play distinct roles and regulate each other to achieve coordinated force production.