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Mol Cell. 2000 Dec;6(6):1515-21.

Visualization of substrate binding and translocation by the ATP-dependent protease, ClpXP.

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Laboratory of Structural Biology, National Institute of Arthritis, Musculoskeletal, and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA.


Binding and internalization of a protein substrate by E. coli ClpXP was investigated by electron microscopy. In sideviews of ATP gamma S-stabilized ClpXP complexes, a narrow axial channel was visible in ClpX, surrounded by protrusions on its distal surface. When substrate lambda O protein was added, extra density attached to this surface. Upon addition of ATP, this density disappeared as lambda O was degraded. When ATP was added to proteolytically inactive ClpXP-lambda O complexes, the extra density transferred to the center of ClpP and remained inside ClpP after separation from ClpX. We propose that substrates of ATP-dependent proteases bind to specific sites on the distal surface of the ATPase, and are subsequently unfolded and translocated into the internal chamber of the protease.

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