Here's the hook: similar substrate binding sites in the chaperone domains of Clp and Lon.

Abstract

Protein quality control mechanisms are essential to ensure the proper levels of functional proteins within the cell and to eliminate nonfunctional proteins from the cell. To this end, the cell maintains an array of molecular chaperones to help fold proteins into their native conformations, prevent aggregation, and assist in assembly of multiprotein complexes, along with ATP-dependent proteases to degrade damaged or improperly synthesized proteins (reviewed in refs. 1–4). Also, the intracellular concentrations or activities of a limited number of normal cellular proteins are modulated by these same proteases and chaperones. These natural protein targets are often key regulatory proteins involved in vital processes such as cell division, stress responses, and developmental changes. To avoid potentially lethal damage to inappropriate cellular components, the chaperones and proteases have evolved rather complex energy-dependent mechanisms to assure accurate substrate recognition.