Skating on MTs

10.1083/jcb.1726rr1jcb.1726rr1Kendall [email protected] on MTs D ynactin can skate along the length of a microtubule (MT), giving a boost to the attached dynein motor’s forward progress, according to Tara Culver-Hanlon, Stephen King (University of Missouri, Kansas City, MO), and colleagues. Dynein is a poorly processive motor compared with others like kinesin. “It doesn’t stay on the microtubule worth a hoot,” says King. To be effi cient, dynein needs dynactin, which has its own MT-binding domains. King’s group found that dynactin had not only the wellknown CAP-Gly MT-binding domain, but also a neighboring basic domain that bound MTs. When the group attached the domains to beads for single-particle tracking along MTs, the beads moved in distinctly different ways. CAPGly beads missing the basic sequence only swiveled around a relatively fi xed point on the MT. Beads with only the basic domain or with both domains could swivel too, but they also skated the length of the MT track while still bound to it. When the dynein motor was added to the mix, the basic domain alone or full-length dynactin increased the motor’s processivity. The CAP-Gly domain alone, however, put the brakes on the motor’s speed. The basic domain acts like a space-walking astronaut’s tether, says King. “When dynein falls off, [the motor] can rebind and keep moving instead of fl oating off into the cytoplasm.”