Jason L. Choy Laboratory of Single Molecule Biophysics, University of California, Berkeley, Berkeley, United States; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
Gheorghe Chistol
Jason L. Choy Laboratory of Single Molecule Biophysics, University of California, Berkeley, Berkeley, United States; Department of Physics, University of California, Berkeley, Berkeley, United States
Yuanbo Cui
Jason L. Choy Laboratory of Single Molecule Biophysics, University of California, Berkeley, Berkeley, United States; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States
Jason L. Choy Laboratory of Single Molecule Biophysics, University of California, Berkeley, Berkeley, United States; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States; Department of Physics, University of California, Berkeley, Berkeley, United States; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States; Department of Chemistry and Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, United States; Kavli Energy NanoSciences Institute at the University of California, Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, United States
Multi-subunit ring-shaped ATPases are molecular motors that harness chemical free energy to perform vital mechanical tasks such as polypeptide translocation, DNA unwinding, and chromosome segregation. Previously we reported the intersubunit coordination and stepping behavior of the hexameric ring-shaped ATPase SpoIIIE (Liu et al., 2015). Here we use optical tweezers to characterize the motor’s mechanochemistry. Analysis of the motor response to external force at various nucleotide concentrations identifies phosphate release as the likely force-generating step. Analysis of SpoIIIE pausing indicates that pauses are off-pathway events. Characterization of SpoIIIE slipping behavior reveals that individual motor subunits engage DNA upon ATP binding. Furthermore, we find that SpoIIIE’s velocity exhibits an intriguing bi-phasic dependence on force. We hypothesize that this behavior is an adaptation of ultra-fast motors tasked with translocating DNA from which they must also remove DNA-bound protein roadblocks. Based on these results, we formulate a comprehensive mechanochemical model for SpoIIIE.
