Biology Department Seminar

ClpX is a AAA+ molecular machine that uses energy derived from ATP hydrolysis to power the unfolding of stable proteins and the translocation of unfolded polypeptides in to the ClpP peptidase. Crystal structures of E.coli ClpX reveal a strikingly asymmetric and non-planar architecture that arises from large rotations occurring between domains of individual monomers. These rotations destroy two of the six potential nucleotide-binding sites and place the conserved translocating loops in a staggered arrangement around the central pore. Moreover, soaking experiments show complex nucleotide-dependent motions within crystals that drive axial movement of the translocating loops. Engineered physical constraints have been used to identify a stable rigid-body coupling that allows the enzyme to efficiently propagate motions around the hexameric ring. Together, these experiments provide a rationale for how ClpX is able to cycle through discrete conformational states to allow the coupling of ATP hydrolysis to the generation of mechanical work.