Single-molecule observation of nucleotide induced conformational changes in basal SecA-ATP hydrolysis

11 pages ; illustrationsSecA is the critical adenosine triphosphatase that drives preprotein transport through the translocon, SecYEG, in Escherichia coli. This process is thought to be regulated by conformational changes of specific domains of SecA, but real-time, real-space measurement of these changes is lacking. We use single-molecule atomic force microscopy (AFM) to visualize nucleotide-dependent conformations and conformational dynamics of SecA. Distinct topographical populations were observed in the presence of specific nucleotides. AFM investigations during basal adenosine triphosphate (ATP) hydrolysis revealed rapid, reversible transitions between a compact and an extended state at the ~100-ms time scale. A SecA mutant lacking the precursor-binding domain (PBD) aided interpretation. Further, the biochemical activity of SecA prepared for AFM was confirmed by tracking inorganic phosphate release. We conclude that ATP-driven dynamics are largely due to PBD motion but that other segments of SecA contribute to this motion during the transition state of the ATP hydrolysis cycle.Funding: This work was supported by the National Science Foundation (CAREER award number 1054832 to G.M.K.) and a Burroughs Wellcome Fund Career Award at the Scientific Interface (to G.M.K.)Nagaraju Chada1*, Kanokporn Chattrakun1, Brendan P. Marsh1†, Chunfeng Mao2, Priya Bariya2, Gavin M. King1,2‡: 1Department of Physics and Astronomy, University of Missouri–Columbia, Columbia, MO 65211, USA. 2Department of Biochemistry, University of Missouri–Columbia, Columbia, MO 65211, USA. *Present address: Department of Biology, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA. †Present address: Department of Applied Physics, Stanford University, Stanford, CA 94305 USA. ‡Corresponding author.Nagaraju Chada (1*), Kanokporn Chattrakun (1), Brendan P. Marsh (1†), Chunfeng Mao (2), Priya Bariya (2), Gavin M. King (1,2‡) -- References: 1) Department of Physics and Astronomy, University of Missouri–Columbia, Columbia,MO 65211, USA ; 2) Department of Biochemistry, University of Missouri–Columbia, Columbia, MO 65211, USA ; *) Present address: Department of Biology, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA ; †) Present address: Department of Applied Physics, Stanford University, Stanford, CA 94305 USA ; ‡) Corresponding author

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