Immunochemical studies on the Clp-protease in chloroplasts: Evidence for the formation of a ClpC/P complex

Chloroplasts contain a proteolytic system whose activity is ATP-dependent. The presence of genes encoding homologues of the ATP-dependent E.coli ClpA/P protease on the plastome and nuclear genome suggests that a similar protease is located in chloroplasts. Antibodies raised against a recombinant chloroplast-encoded proteolytic ClpP subunit detect this polypeptide in chloroplasts prepared from barley leaves or the eukaryotic algae Chlamydomonos reinhardtii and Eugleno gracitis. Co-immunoprecipitation experiments using the anti-ClpP antibody and an antibody against the nuclear encoded regulatory ClpC component (a ClpA homologue) provide direct evidence for the existence of a ClpC/P complex in the chloroplast stroma. These results suggest that at least a part of the ATP-dependent proteolytic reactions in the chloroplast is catalyzed by an enzyme complex similar to the E.coli ClpA/P protease.