ClpXP, an ATP-powered unfolding and protein-degradation machine

► Ring hexamers of ClpX unfold and then translocate proteins into ClpP for degradation. ► A narrow pore restricts ClpP activity unless ClpX/ClpA or acyldepsipeptides bind. ► ClpX recognizes peptide tags or degrons in protein substrates and adaptor proteins. ► Asymmetric ATP hydrolysis by one ClpX subunit powers mechanical protein unfolding. ► Crystallography and single-molecule results reveal detailed aspects of mechanism.