title: Conformational transitions in DNA polymerase I revealed by single-molecule FRET.
abstract: The remarkable fidelity of most DNA polymerases depends on a series of early steps in the reaction pathway which allow the selection of the correct nucleotide substrate, while excluding all incorrect ones, before the enzyme is committed to the chemical step of nucleotide incorporation. The conformational transitions that are involved in these early steps are detectable with a variety of fluorescence assays and include the fingers-closing transition that has been characterized in structural studies. Using DNA polymerase I (Klenow fragment) labeled with both donor and acceptor fluorophores, we have employed single-molecule fluorescence resonance energy transfer to study the polymerase conformational transitions that precede nucleotide addition. Our experiments clearly distinguish the open and closed conformations that predominate in Pol-DNA and Pol-DNA-dNTP complexes, respectively. By contrast, the unliganded polymerase shows a broad distribution of FRET values, indicating a high degree of conformational flexibility in the protein in the absence of its substrates; such flexibility was not anticipated on the basis of the available crystallographic structures. Real-time observation of conformational dynamics showed that most of the unliganded polymerase molecules sample the open and closed conformations in the millisecond timescale. Ternary complexes formed in the presence of mismatched dNTPs or complementary ribonucleotides show unique FRET species, which we suggest are relevant to kinetic checkpoints that discriminate against these incorrect substrates.
authors.affiliation: Biological Physics Research Group, Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, United Kingdom.
authors.forename: Yusdi
authors.initials: Y
authors.lastname: Santoso
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Joyce
authors.forename: Olga
authors.initials: O
authors.lastname: Potapova
authors.forename: Ludovic
authors.initials: L
authors.lastname: Le Reste
authors.forename: Johannes
authors.initials: J
authors.lastname: Hohlbein
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Torella
authors.forename: Nigel D F
authors.initials: ND
authors.lastname: Grindley
authors.forename: Achillefs N
authors.initials: AN
authors.lastname: Kapanidis
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D003198:Computer Simulation; D004256:DNA Polymerase I / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods*; D001411:Geobacillus stearothermophilus / Q000201:enzymology; D007700:Kinetics; D018613:Microscopy, Confocal; D008958:Models, Molecular; D011487:Protein Conformation; D017384:Sequence Deletion
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D004256:DNA Polymerase I