NorQD AAA+ complex drives metal insertion by a twisting mechanism.

Abstract

ATPases associated with diverse cellular activities (AAA+ -ATPases) catalyse a wide range of remodelling events in all phyla. AAA+ -ATPases of the MoxR-like family typically co-operate with von Willebrand factor type A (VWA) domain containing proteins to facilitate target remodelling and metal ion insertion, but their mechanism of action is poorly understood. We studied the bacterial AAA+ -ATPase NorQ in complex with its VWA domain partner protein NorD, which are essential for nitric oxide reductase (NOR) activity. Our cryo-EM structures and biochemical analyses show that NorQ and NorD engage through two key interfaces: (i) a finger-like extension protruding from the VWA domain that penetrates the central pore of the NorQ hexamer, and (ii) the NorD C- terminus, which contacts the post-sensor 1 loop of NorQ. Our data reveal that NorQ activity remodels a linker region in NorD essential for metal insertion. Together, these findings support a model in which the NorQ complex exerts a twisting and stretching force on the NorD linker, thereby enabling metal insertion into its target NOR.