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  • 1
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    Combining H/D exchange mass spectroscopy and computational docking reveals extended DNA-binding surface on uracil-DNA glycosylase (2012)
    Oxford University Press
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    Publication Date: 2012-07-22
    Description: X-ray crystallography provides excellent structural data on protein–DNA interfaces, but crystallographic complexes typically contain only small fragments of large DNA molecules. We present a new approach that can use longer DNA substrates and reveal new protein–DNA interactions even in extensively studied systems. Our approach combines rigid-body computational docking with hydrogen/deuterium exchange mass spectrometry (DXMS). DXMS identifies solvent-exposed protein surfaces; docking is used to create a 3-dimensional model of the protein–DNA interaction. We investigated the enzyme uracil-DNA glycosylase (UNG), which detects and cleaves uracil from DNA. UNG was incubated with a 30 bp DNA fragment containing a single uracil, giving the complex with the abasic DNA product. Compared with free UNG, the UNG–DNA complex showed increased solvent protection at the UNG active site and at two regions outside the active site: residues 210–220 and 251–264. Computational docking also identified these two DNA-binding surfaces, but neither shows DNA contact in UNG–DNA crystallographic structures. Our results can be explained by separation of the two DNA strands on one side of the active site. These non-sequence-specific DNA-binding surfaces may aid local uracil search, contribute to binding the abasic DNA product and help present the DNA product to APE-1, the next enzyme on the DNA-repair pathway.
    Keywords: Protein-nucleic acid interaction
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 2
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    Competitive binding-based optical DNA mapping for fast identification of bacteria - multi-ligand transfer matrix theory and experimental applications on Escherichia coli (2014)
    Oxford University Press
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    Publication Date: 2014-09-02
    Description: We demonstrate a single DNA molecule optical mapping assay able to resolve a specific Escherichia coli strain from other strains. The assay is based on competitive binding of the fluorescent dye YOYO-1 and the AT-specific antibiotic netropsin. The optical map is visualized by stretching the DNA molecules in nanofluidic channels. We optimize the experimental conditions to obtain reproducible barcodes containing as much information as possible. We implement a multi-ligand transfer matrix method for calculating theoretical barcodes from known DNA sequences. Our method extends previous theoretical approaches for competitive binding of two types of ligands to many types of ligands and introduces a recursive approach that allows long barcodes to be calculated with standard computer floating point formats. The identification of a specific E . coli strain (CCUG 10979) is based on mapping of 50–160 kilobasepair experimental DNA fragments onto the theoretical genome using the developed theory. Our identification protocol introduces two theoretical constructs: a P -value for a best experiment-theory match and an information score threshold. The developed methods provide a novel optical mapping toolbox for identification of bacterial species and strains. The protocol does not require cultivation of bacteria or DNA amplification, which allows for ultra-fast identification of bacterial pathogens.
    Keywords: Protein-nucleic acid interaction
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 3
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    Single-molecule sorting reveals how ubiquitylation affects substrate recognition and activities of FBH1 helicase (2013)
    Oxford University Press
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    Publication Date: 2013-04-02
    Description: DNA repair helicases function in the cell to separate DNA duplexes or remodel nucleoprotein complexes. These functions are influenced by sensing and signaling; the cellular pool of a DNA helicase may contain subpopulations of enzymes carrying different post-translational modifications and performing distinct biochemical functions. Here, we report a novel experimental strategy, single-molecule sorting, which overcomes difficulties associated with comprehensive analysis of heterologously modified pool of proteins. This methodology was applied to visualize human DNA helicase F-box–containing DNA helicase (FBH1) acting on the DNA structures resembling a stalled or collapsed replication fork and its interactions with RAD51 nucleoprotein filament. Individual helicase molecules isolated from human cells with their native post-translational modifications were analyzed using total internal reflection fluorescence microscopy. Separation of the activity trajectories originated from ubiquitylated and non-ubiquitylated FBH1 molecules revealed that ubiquitylation affects FBH1 interaction with the RAD51 nucleoprotein filament, but not its translocase and helicase activities.
    Keywords: Protein-nucleic acid interaction
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 4
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    Real-time single-molecule studies of the motions of DNA polymerase fingers illuminate DNA synthesis mechanisms (2015)
    Oxford University Press
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    Publication Date: 2015-07-12
    Description: DNA polymerases maintain genomic integrity by copying DNA with high fidelity. A conformational change important for fidelity is the motion of the polymerase fingers subdomain from an open to a closed conformation upon binding of a complementary nucleotide. We previously employed intra-protein single-molecule FRET on diffusing molecules to observe fingers conformations in polymerase–DNA complexes. Here, we used the same FRET ruler on surface-immobilized complexes to observe fingers-opening and closing of individual polymerase molecules in real time. Our results revealed the presence of intrinsic dynamics in the binary complex, characterized by slow fingers-closing and fast fingers-opening. When binary complexes were incubated with increasing concentrations of complementary nucleotide, the fingers-closing rate increased, strongly supporting an induced-fit model for nucleotide recognition. Meanwhile, the opening rate in ternary complexes with complementary nucleotide was 6 s –1 , much slower than either fingers closing or the rate-limiting step in the forward direction; this rate balance ensures that, after nucleotide binding and fingers-closing, nucleotide incorporation is overwhelmingly likely to occur. Our results for ternary complexes with a non-complementary dNTP confirmed the presence of a state corresponding to partially closed fingers and suggested a radically different rate balance regarding fingers transitions, which allows polymerase to achieve high fidelity.
    Keywords: Protein-nucleic acid interaction
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 5
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    High-throughput single-molecule analysis of DNA-protein interactions by tethered particle motion (2012)
    Oxford University Press
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    Publication Date: 2012-06-28
    Description: Tethered particle motion (TPM) monitors the variations in the effective length of a single DNA molecule by tracking the Brownian motion of a bead tethered to a support by the DNA molecule. Providing information about DNA conformations in real time, this technique enables a refined characterization of DNA–protein interactions. To increase the output of this powerful but time-consuming single-molecule assay, we have developed a biochip for the simultaneous acquisition of data from more than 500 single DNA molecules. The controlled positioning of individual DNA molecules is achieved by self-assembly on nanoscale arrays fabricated through a standard microcontact printing method. We demonstrate the capacity of our biochip to study biological processes by applying our method to explore the enzymatic activity of the T7 bacteriophage exonuclease. Our single molecule observations shed new light on its behaviour that had only been examined in bulk assays previously and, more specifically, on its processivity.
    Keywords: Protein-nucleic acid interaction
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 6
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    Snapshots of pre-rRNA structural flexibility reveal eukaryotic 40S assembly dynamics at nucleotide resolution (2014)
    Oxford University Press
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    Publication Date: 2014-11-07
    Description: Ribosome assembly in eukaryotes involves the activity of hundreds of assembly factors that direct the hierarchical assembly of ribosomal proteins and numerous ribosomal RNA folding steps. However, detailed insights into the function of assembly factors and ribosomal RNA folding events are lacking. To address this, we have developed ChemModSeq, a method that combines structure probing, high-throughput sequencing and statistical modeling, to quantitatively measure RNA structural rearrangements during the assembly of macromolecular complexes. By applying ChemModSeq to purified 40S assembly intermediates we obtained nucleotide-resolution maps of ribosomal RNA flexibility revealing structurally distinct assembly intermediates and mechanistic insights into assembly dynamics not readily observed in cryo-electron microscopy reconstructions. We show that RNA restructuring events coincide with the release of assembly factors and predict that completion of the head domain is required before the Rio1 kinase enters the assembly pathway. Collectively, our results suggest that 40S assembly factors regulate the timely incorporation of ribosomal proteins by delaying specific folding steps in the 3' major domain of the 20S pre-ribosomal RNA.
    Keywords: Protein-nucleic acid interaction
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 7
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    DNA target sequence identification mechanism for dimer-active protein complexes (2013)
    Oxford University Press
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    Publication Date: 2013-02-20
    Description: Sequence-specific DNA-binding proteins must quickly and reliably localize specific target sites on DNA. This search process has been well characterized for monomeric proteins, but it remains poorly understood for systems that require assembly into dimers or oligomers at the target site. We present a single-molecule study of the target-search mechanism of protelomerase TelK, a recombinase-like protein that is only active as a dimer. We show that TelK undergoes 1D diffusion on non-target DNA as a monomer, and it immobilizes upon dimerization even in the absence of a DNA target site. We further show that dimeric TelK condenses non-target DNA, forming a tightly bound nucleoprotein complex. Together with theoretical calculations and molecular dynamics simulations, we present a novel target-search model for TelK, which may be generalizable to other dimer and oligomer-active proteins.
    Keywords: Protein-nucleic acid interaction
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 8
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    Unbiased proteomic analysis of proteins interacting with the HIV-1 5'LTR sequence: role of the transcription factor Meis (2012)
    Oxford University Press
    Details
    Publication Date: 2012-11-25
    Description: To depict the largest picture of a core promoter interactome, we developed a one-step DNA-affinity capture method coupled with an improved mass spectrometry analysis process focused on the identification of low abundance proteins. As a proof of concept, this method was developed through the analysis of 230 bp contained in the 5'long terminal repeat (LTR) of the human immunodeficiency virus 1 (HIV-1). Beside many expected interactions, many new transcriptional regulators were identified, either transcription factors (TFs) or co-regulators, which interact directly or indirectly with the HIV-1 5'LTR. Among them, the homeodomain-containing TF myeloid ectopic viral integration site was confirmed to functionally interact with a specific binding site in the HIV-1 5'LTR and to act as a transcriptional repressor, probably through recruitment of the repressive Sin3A complex. This powerful and validated DNA-affinity approach could also be used as an efficient screening tool to identify a large set of proteins that physically interact, directly or indirectly, with a DNA sequence of interest. Combined with an in silico analysis of the DNA sequence of interest, this approach provides a powerful approach to select the interacting candidates to validate functionally by classical approaches.
    Keywords: Protein-nucleic acid interaction
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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