HOMOLOGY IN STRUCTURAL ORGANIZATION BETWEEN ESCHERICHIA-COLI CLPAP PROTEASE AND THE EUKARYOTIC 26S-PROTEASOME

Energy-dependent protein degradation is carried out by large multimeri c protein complexes such as the proteasomes of eukaryotic and archaeal cells and the ATP-dependent proteases of eubacterial cells. Clp prote ase, a major multicomponent protease of Escherichia coli, consists of a proteolytic component, ClpP, in association with an ATP-hydrolyzing, chaperonin-like component, ClpA. To provide a structural basis for un derstanding the regulation and mechanism of action of Clp protease, we have used negative staining electron microscopy and image analysis to examine ClpA and ClpP separately, as well as active ClpAP complexes. Digitized images of ClpP and ClpA were analyzed using a novel algorith m designed to detect rotational symmetries. ClpP is composed of two ri ngs of seven subunits superimposed in bipolar fashion along the axis o f rotational symmetry. This structure is similar to that formed by the beta subunits of the eukaryotic and archaeal proteasomes. In the pres ence of MgATP, ClpA forms an oligomer with 6-fold symmetry When viewed en face. Side views of ClpA indicate that the subunits are bilobed wi th the respective domains forming two stacked rings. ClpAP complexes c ontain a tetradecamer of ClpP flanked at one or both ends with a hexam er of ClpA, resulting in a symmetry mismatch between the axially align ed molecules. Our findings demonstrate that, despite the lack of seque nce similarity between ClpAP and proteasomes, these multimeric proteas es nevertheless have a profound similarity in their underlying archite cture that may reflect a common mechanism of action. (C) 1995 Academic Press Limited