ATP-promoted interaction between Clp A and Clp P in activation of Clp protease from Escherichia coli

Abstract

Clp protease is a high relative molecular mass, ATP-dependent protease found in the cytoplasm of Escherichia coli. Clp protease is composed of two protein components, Clp A, which has ATPase activity, and Clp P, which has the proteolytic active site and is activated by Clp A in the presence of ATP. Clp P subunits (Mr = 21,500) are arranged in two hexagonal rings directly superimposed on each other, and under low salt conditions two dodecamers associate to form a particle with Mr approximately 440,000. Clp A (subunit Mr = 83,000) and Clp P do not associate in the absence of nucleotide, but Clp A with ATP bound associates with Clp P to form an active proteolytic complex with Mr approximately 700,000. Although adenosine 5'-[beta gamma-imido]triphosphate (AMPPNP) weakly promotes association between Clp A and Clp P, non-hydrolysable analogues of ATP do not activate proteolysis, indicating that association between the components is not sufficient to allow proteolysis. Association between Clp A and Clp P does not alter the basal ATPase activity of Clp A, but addition of protein substrates is accompanied by an increase in ATP hydrolysis by Clp A. Chemically-inactivated Clp P or inactive mutants of Clp P also associate with Clp A, but no increase in the ATPase activity of Clp A is observed, either in the presence or absence of protein substrates, when Clp P is inactive. Thus the increased ATP hydrolysis is dependent on active proteolysis.(ABSTRACT TRUNCATED AT 250 WORDS)