Practice question

Dynein stepping mechanism contrasts with kinesin neck-linker model, employing large AAA ring plus linker swing. In absence of nucleotide, microtubule-binding domain tightly bound, linker straight docking at AAA5. ATP binding to AAA1 induces closure of AAA1-AAA2 interface, pulling buttress from AAA5 that shifts stalk coiled-coil registry from alpha to beta, weakening microtubule affinity and detaching motor. Hydrolysis allows linker undocking from AAA5 and migration toward AAA2 site forming pre power stroke bent conformation. Forward diffusion and microtubule rebinding triggers release of phosphate, conformational relaxation pulling AAA2-AAA3, generating strain that drives linker back toward AAA5, producing power stroke that moves tail forward. ADP release completes cycle. Thus movement specifically results from coordinated ADP release coupled linker rotation and registry-controlled microtubule affinity switching. No myosin binding occurs, GTP irrelevant because catalytic pocket specific for adenine, oligomeric filament formation unnecessary because dimeric motor processive via alternating heads anchored to dynactin cargo complex. Integration with cell cycle kinases, calcium signaling and mechanical cues ensures coordinated remodeling during growth, migration and differentiation.