Practice question

Linker domain is a four helix bundle lever that spans AAA ring, mechanically linking tail to motor. In post power stroke conformation it is straight, docked near AAA5, positioning cargo forward. ATP binding to AAA1 induces closure of ring and steric clash pushing linker off AAA5 toward AAA2 docking site, forming bent pre power stroke state that primes motor. This repositioning stores elastic strain. Upon microtubule rebinding and ADP release, linker snaps back toward AAA5, executing forceful swing that drags cargo complex relative to microtubule by several nanometers. Because length exceeds 10 nanometers, small conformational changes at AAA1 amplified into large displacement. It contains no microtubule-binding motifs; those reside in stalk tip microtubule-binding domain. It never contacts actin filaments. Artificial insertion of flexible hinges or deletion uncouples ATPase activity from translocation, yielding motors that hydrolyze ATP futilely without movement, proving linker functions as transmission rod converting hydrolysis energy into directed mechanical work rather than scaffolding.