Importance of heptameric ring integrity for activity of Escherichia coli ClpP

Radiation target analysis has been used to identify the minimal functional unit for expression of activity of ClpP, the proteolytic component of the A TP-dependent ClpAP protease. Radiation target sizes determined for small pe ptide hydrolysis, for ClpA-activated and nucleotide-activated oligopeptide cleavage, and for ClpA-activated ATP-dependent protein degradation were 154 , 118, and 160 kDa, respectively. Thus, the hydrolytic activity of ClpP, su bunit M-r 21500, is dependent on the native oligomeric structure. The quate rnary structure of ClpP determined by electron microscopy and hydrodynamic studies consists of two face-to-face seven-membered rings. The radiation ta rget sizes are consistent with a requirement for conformational integrity o f an entire ring for expression of hydrolytic activity. Radiation damage le d to disruption of inter-ring contacts, giving rise to isolated rings of Cl pP. Thus, contacts between rings of ClpP are less stable and more easily di srupted than contacts between subunits within the rings. Our data suggest t hat cooperative interactions between subunits within the ClpP rings are imp ortant for maintaining the active conformation of the proteolytic active si te.