title: Motor step size and ATP coupling efficiency of the dsDNA translocase EcoR124I.
abstract: The Type I restriction-modification enzyme EcoR124I is an archetypical helicase-based dsDNA translocase that moves unidirectionally along the 3'-5' strand of intact duplex DNA. Using a combination of ensemble and single-molecule measurements, we provide estimates of two physicochemical constants that are fundamental to a full description of motor protein activity-the ATP coupling efficiency (the number of ATP consumed per base pair) and the step size (the number of base pairs transported per motor step). Our data indicate that EcoR124I makes small steps along the DNA of 1 bp in length with 1 ATP consumed per step, but with some uncoupling of the ATPase and translocase cycles occurring so that the average number of ATP consumed per base pair slightly exceeds unity. Our observations form a framework for understanding energy coupling in a great many other motors that translocate along dsDNA rather than ssDNA.
authors.affiliation: Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands.
authors.forename: Ralf
authors.initials: R
authors.lastname: Seidel
authors.forename: Joost G P
authors.initials: JG
authors.lastname: Bloom
authors.forename: Cees
authors.initials: C
authors.lastname: Dekker
authors.forename: Mark D
authors.initials: MD
authors.lastname: Szczelkun
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D015253:Deoxyribonucleases, Type I Site-Specific / Q000378:metabolism*; D005470:Fluorometry; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D000255:Adenosine Triphosphate; D004247:DNA; C048242:endodeoxyribonuclease EcoR124I; D015253:Deoxyribonucleases, Type I Site-Specific; D000251:Adenosine Triphosphatases