Enzymatic and Structural Similarities between theEscherichia coli ATP-dependent Proteases, ClpXP and ClpAP

Abstract

Escherichia coli ClpX, a member of the Clp family of ATPases, has ATP-dependent chaperone activity and is required for specific ATP-dependent proteolytic activities expressed by ClpP. Gel filtration and electron microscopy showed that ClpX subunits (M r 46,000) associate to form a six-membered ring (M r ϳ 280,000) that is stabilized by binding of ATP or nonhydrolyzable analogs of ATP. ClpP, which is composed of two seven-membered rings stacked face-to-face, interacts with the nucleotide-stabilized hexamer of ClpX to form a complex that could be isolated by gel filtration. Electron micrographs of negatively stained ClpXP preparations showed side views of 1:1 and 2:1 ClpXP complexes in which ClpP was flanked on either one or both sides by a ring of ClpX. Thus, as was seen for ClpAP, a symmetry mismatch exists in the bonding interactions between the seven-membered rings of ClpP and the six-membered rings of ClpX. Competition studies showed that ClpA may have a slightly higher affinity (ϳ2-fold) for binding to ClpP. Mixed complexes of ClpA, ClpX, and ClpP with the two ATPases bound simultaneously to opposite faces of a single ClpP molecule were seen by electron microscopy. In the presence of ATP or nonhydrolyzable analogs of ATP, ClpXP had nearly the same activity as ClpAP against oligopeptide substrates (>10,000 min ؊1

AAA+ Chaperone ClpX Regulates Dynamics of Prokaryotic Cytoskeletal Protein FtsZ

“…4B). These observations are consistent with a previous report showing that ClpX showed heterogeneously sized particles with no obvious regularity and that the addition of ATP␥S to ClpX produced a more uniform particle with a size corresponding to a hexamer (30).…”

Crystal Structure of ClpX Molecular Chaperone from Helicobacter pylori

“…Hexameric Assembly of Hp ClpX-ASD-Since E. coli ClpX and E. coli ClpX-ASD were observed as six-membered ring structures, by electron microscopy (7,35), and the Hp ClpX-ASD also confirmed to form a hexameric structure in solution, it is appropriate to construct a hexameric model of Hp ClpX-ASD to explain its biological implication.…”

Crystal structure of Mycobacterium tuberculosis ClpP1P2 suggests a model for peptidase activation by AAA+ partner binding and substrate delivery

“…The existence of discrete M. tuberculosis ClpP1 and ClpP2 rings might allow specialization compared with homomeric ClpPs, in which each ring normally can interact with several AAA+ partners (36). For example, structural differences between the LGFbinding pockets and N-loops of the ClpP1 and ClpP2 rings could result in ClpX binding to one ring and ClpC1 to the other ring, perhaps as a way to balance the degradation of substrates recognized by each AAA+ partner.…”