Requirement of ATP Hydrolysis for Assembly of ClpA/ClpP Complex, the ATP-Dependent Protease Ti in Escherichia coli

The ATP-dependent protease Ti (Clp) consists of two distinct components, ClpP containing the serine active sites for proteolysis and ClpA having two ATP-binding sites. A ClpA variant (ClpAT) carrying Thr in place of Met 169 is highly soluble but indistinguishable from the wild-type ClpA in its ability to hydrolyze ATP and to support the ClpP-mediated proteolysis. Here we show that ATP hydrolysis is essential for assembly of ClpAT/ClpP complex upon analysis of the mixture of its components by gel filtration followed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate Either ADP or adenosine 5′-(β,γ-imido)-triphosphate could not support the complex formation. Furthermore, ClpAT/K501T which carries a mutation in the second ATP-binding site and therefore is unable to cleave ATP could not interact with ClpP. On the other hand, ClpAT/K220T carrying a mutation in the first site and ClpP could be assembled into a complex at 2 mM ATP but not at 0.5 mM, at which concentration the trimeric mutant protein can not form a hexamer. These results indicate that assembly of protease Ti requires hydrolysis of ATP by ClpA in addition to its binding for hexamer formation.