ClpAP and ClpXP Proteinases

These large ATP-dependent proteinases are involved in protein degradation in prokaryotes. Each enzyme is composed of two subcomplexes, both of which are essential for ATP-dependent proteolysis. (A similar enzyme system is also found in chloroplasts of plant.(

1. ClpP

 The ClpP proteolytic component is a serine proteinase composed of 14 identical subunits, organized in two seven-membered rings. The rings enclose a central chamber where the active sites are localized. To be degraded, proteins must enter this chamber through openings in the rings. By itself, ClpP can hydrolyze small peptides but not polypeptides. To degrade proteins, this proteolytic component must associate with either of two homologous ATPase complexes (ClpA or ClpX), which determine the substrate specificity.

 2. ClpA and ClpX

ClpA and ClpX complexes are hexameric rings that associate with each end of the ClpP to form a four-ring active enzyme. These ATPases bind different types of polypeptides, probably unfold them, and facilitate their entry into ClpP for degradation.