The functional oligomeric state of the HsClpXP complexconsists of 14 HsClpP subunits forming a cylinder of twoheptameric rings (Figure 1Bi) that is capped at each end by sixHsClpX subunits forming the hexameric ring5 typical of AAA+ATPases. In this configuration, the catalytic residues ofHsClpP (Ser153, His178, and Asp227) (Figure 1Bii) areenclosed within the lumen of the ClpP cylinder to preventunspecific proteolytic activities,9 while HsClpX serves as thegatekeeper that recognizes only specific proteins and targetsthem for degradation4 (Figure 1C). The interaction betweenthe HsClpX and HsClpP oligomers is stabilized by the highlydynamic docking interactions of the ATPase’s IGF loops(L439-G440-F441 within the E436−G450 region of HsClpX)with the hydrophobic pockets formed by neighboring HsClpPsubunits at the ClpX−ClpP interface.10