title: Taking a molecular motor for a spin: helicase mechanism studied by spin labeling and PELDOR.
abstract: The complex molecular motions central to the functions of helicases have long attracted attention. Protein crystallography has provided transformative insights into these dynamic conformational changes, however important questions about the true nature of helicase configurations during the catalytic cycle remain. Using pulsed EPR (PELDOR or DEER) to measure interdomain distances in solution, we have examined two representative helicases: PcrA from superfamily 1 and XPD from superfamily 2. The data show that PcrA is a dynamic structure with domain movements that correlate with particular functional states, confirming and extending the information gleaned from crystal structures and other techniques. XPD in contrast is shown to be a rigid protein with almost no conformational changes resulting from nucleotide or DNA binding, which is well described by static crystal structures. Our results highlight the complimentary nature of PELDOR to crystallography and the power of its precision in understanding the conformational changes relevant to helicase function.
authors.affiliation: Biomedical Sciences Research Complex, University of St Andrews, Fife KY16 9ST, UK.
authors.forename: Diana
authors.initials: D
authors.lastname: Constantinescu-Aruxandei
authors.affiliation: Biomedical Sciences Research Complex, University of St Andrews, Fife KY16 9ST, UK.
authors.forename: Biljana
authors.initials: B
authors.lastname: Petrovic-Stojanovska
authors.affiliation: Institute of Physical and Theoretical Chemistry, University of Bonn, Wegelerstrasse 12, 53115 Bonn, Germany.
authors.forename: Olav
authors.initials: O
authors.lastname: Schiemann
authors.affiliation: Biomedical Sciences Research Complex, University of St Andrews, Fife KY16 9ST, UK mfw2@st-and.ac.uk.
authors.forename: James H
authors.initials: JH
authors.lastname: Naismith
authors.affiliation: Biomedical Sciences Research Complex, University of St Andrews, Fife KY16 9ST, UK mfw2@st-and.ac.uk.
authors.forename: Malcolm F
authors.initials: MF
authors.lastname: White
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004265:DNA Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D001411:Geobacillus stearothermophilus / Q000201:enzymology; D008958:Models, Molecular; D009154:Mutation; D009711:Nucleotides / Q000378:metabolism; D017434:Protein Structure, Tertiary; D013113:Spin Labels; D051759:Xeroderma Pigmentosum Group D Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D009711:Nucleotides; D013113:Spin Labels; C084217:pcrA protein, Bacteria; D004247:DNA; D004265:DNA Helicases; D051759:Xeroderma Pigmentosum Group D Protein; C497292:ERCC2 protein, human