Practice question

Kinesin-1 regulation avoids gratuitous ATP consumption and traffic jams by autoinhibition mechanism evolutionarily conserved ensuring motor only active when bound to cargo. In cargo free state heavy chain tail IAK motif folds back contacting motor head switch regions blocking microtubule stimulated ADP release maintaining ATPase low about 10 fold inhibition. Light chains also contribute to folded globular conformation compact. Cargo adaptors such as JNK interacting proteins JIP1-3 FEZ1 Milton TRAK bind light chains or tail sterically unfolding molecule to extended active state increasing microtubule affinity 20 fold and ATPase rate. ATP hydrolysis itself occurs in motor domain P loop driving stepping not in stalk domain which serves purely structural coiled coil dimerization role linking heads. Thus activation triggered by cargo binding induced unfolding not stalk ATP hydrolysis. ATP hydrolysis at motor provides energy for movement. This regulatory paradigm ensures motor travels only when loaded linking ATP cycles to cargo availability for processive anterograde movement failure leads to organelle mislocalization neurodegeneration and developmental defects.