ClpAP proteolysis does not require rotation of the ClpA unfoldase relative to ClpP

AAA+ proteases, which perform regulated protein degradation in all kingdoms of life, consist of a hexameric AAA+ unfoldase/translocase in complex with a self-compartmentalized peptidase. Based on asymmetric features of cryo-EM structures and a sequential hand-over-hand model of substrate translocation, recent publications have proposed that the AAA+ unfoldases ClpA and ClpX must rotate with respect to their partner peptidase ClpP to allow function. Here, we test this model by covalently crosslinking ClpA to ClpP to prevent rotation. We find that crosslinked ClpAP omplexes unfold, translocate, and degrade protein substrates, albeit modestly slower han uncrosslinked enzyme controls. Rotation of ClpA with respect to ClpP therefore is ot required for ClpAP protease activity, although some flexibility in how the AAA+ ring ocks on ClpP may be necessary for optimal function.