Single-Molecule Protein Unfolding and Translocation by an ATP-Fueled Proteolytic Machine

Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Cell (Impact Factor: 33.12). 04/2011; 145(2):257-67. DOI: 10.1016/j.cell.2011.03.036
Source: PubMed

ABSTRACT All cells employ ATP-powered proteases for protein-quality control and regulation. In the ClpXP protease, ClpX is a AAA+ machine that recognizes specific protein substrates, unfolds these molecules, and then translocates the denatured polypeptide through a central pore and into ClpP for degradation. Here, we use optical-trapping nanometry to probe the mechanics of enzymatic unfolding and translocation of single molecules of a multidomain substrate. Our experiments demonstrate the capacity of ClpXP and ClpX to perform mechanical work under load, reveal very fast and highly cooperative unfolding of individual substrate domains, suggest a translocation step size of 5-8 amino acids, and support a power-stroke model of denaturation in which successful enzyme-mediated unfolding of stable domains requires coincidence between mechanical pulling by the enzyme and a transient stochastic reduction in protein stability. We anticipate that single-molecule studies of the mechanical properties of other AAA+ proteolytic machines will reveal many shared features with ClpXP.

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