Fork sensing and strand switching control antagonistic activities of RecQ helicases
TL;DR: This work investigates the DNA unwinding of RecQ helicases from Arabidopsis thaliana, AtRECQ2 and AtRECZ3 at the single-molecule level using magnetic tweezers and provides a simple explanation for how different biological activities can be achieved by rather similar members of the RecQ family.
Abstract: RecQ helicases have essential roles in maintaining genome stability during replication and in controlling double-strand break repair by homologous recombination. Little is known about how the different RecQ helicases found in higher eukaryotes achieve their specialized and partially opposing functions. Here, we investigate the DNA unwinding of RecQ helicases from Arabidopsis thaliana, AtRECQ2 and AtRECQ3 at the single-molecule level using magnetic tweezers. Although AtRECQ2 predominantly unwinds forked DNA substrates in a highly repetitive fashion, AtRECQ3 prefers to rewind, that is, to close preopened DNA forks. For both enzymes, this process is controlled by frequent strand switches and active sensing of the unwinding fork. The relative extent of the strand switches towards unwinding or towards rewinding determines the predominant direction of the enzyme. Our results provide a simple explanation for how different biological activities can be achieved by rather similar members of the RecQ family.
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TL;DR: A coupling ratio of 1:1 between base pairs unwound and dTTP hydrolysis is suggested, which further support the concept that nucleic acid motors can have a hierarchy of different-sized steps or can accumulate elastic energy before transitioning to a subsequent phase.
54 citations
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...Ce and magnetic tweezers (Klaue et al., 2013; Qi et al., 2013)....
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TL;DR: Techniques such as mutagenesis, chemical modifications, and optogenetics that have been used to re-engineer existing molecular motors to have, for instance, altered speed, processivity, or functionality are reviewed.
Abstract: Molecular motors are diverse enzymes that transduce chemical energy into mechanical work and, in doing so, perform critical cellular functions such as DNA replication and transcription, DNA supercoiling, intracellular transport, and ATP synthesis. Single-molecule techniques have been extensively used to identify structural intermediates in the reaction cycles of molecular motors and to understand how substeps in energy consumption drive transitions between the intermediates. Here, we review a broad spectrum of single-molecule tools and techniques such as optical and magnetic tweezers, atomic force microscopy (AFM), single-molecule fluorescence resonance energy transfer (smFRET), nanopore tweezers, and hybrid techniques that increase the number of observables. These methods enable the manipulation of individual biomolecules via the application of forces and torques and the observation of dynamic conformational changes in single motor complexes. We also review how these techniques have been applied to study various motors such as helicases, DNA and RNA polymerases, topoisomerases, nucleosome remodelers, and motors involved in the condensation, segregation, and digestion of DNA. In-depth analysis of mechanochemical coupling in molecular motors has made the development of artificially engineered motors possible. We review techniques such as mutagenesis, chemical modifications, and optogenetics that have been used to re-engineer existing molecular motors to have, for instance, altered speed, processivity, or functionality. We also discuss how single-molecule analysis of engineered motors allows us to challenge our fundamental understanding of how molecular motors transduce energy.
51 citations
TL;DR: A hybrid single-molecule technique combining magnetic tweezers and Förster resonance energy transfer (FRET) measurements is presented, which induces conformational changes in DNA nanostructures, which are detected in two output channels simultaneously.
Abstract: We present a hybrid single-molecule technique combining magnetic tweezers and Forster resonance energy transfer (FRET) measurements. Through applying external forces to a paramagnetic sphere, we induce conformational changes in DNA nanostructures, which are detected in two output channels simultaneously. First, by tracking a magnetic bead with high spatial and temporal resolution, we observe overall DNA length changes along the force axis. Second, the measured FRET efficiency between two fluorescent probes monitors local conformational changes. The synchronized orthogonal readout in different observation channels will facilitate deciphering the complex mechanisms of biomolecular machines.
47 citations
TL;DR: Force can drive conformational changes in proteins, as well as modulate their stability and the affinity of their complexes, allowing a mechanical input to be converted into a biochemical output.
46 citations
TL;DR: Single-molecule techniques provide the capability to distinguish helicase heterogeneity and monitor helicase motion at nanometer spatial and millisecond temporal resolutions, ultimately providing new insights into the mechanisms that could not be resolved by ensemble assays.
Abstract: Helicases are a diverse group of molecular motors that utilize energy derived from the hydrolysis of nucleoside triphosphates (NTPs) to unwind and translocate along nucleic acids. These enzymes play critical roles in nearly all aspects of nucleic acid metabolism, and consequently, a detailed understanding of helicase mechanisms at the molecular level is essential. Over the past few decades, single-molecule techniques, such as optical tweezers, magnetic tweezers, laminar flow, fluorescence resonance energy transfer (FRET), and DNA curtains, have proved to be powerful tools to investigate the functional properties of both DNA and RNA helicases. These approaches allow researchers to manipulate single helicase molecules, perturb their free energy landscape to probe the chemo-mechanical activities of these motors, and to detect the conformational changes of helicases during unwinding. Furthermore, these techniques also provide the capability to distinguish helicase heterogeneity and monitor helicase motion at nanometer spatial and millisecond temporal resolutions, ultimately providing new insights into the mechanisms that could not be resolved by ensemble assays. This review outlines the single-molecule techniques that have been utilized for measurements of helicase activities and discusses helicase mechanisms with a focus on functional and mechanistic insights revealed through single-molecule investigations in the past five years.
40 citations
Cites background from "Fork sensing and strand switching c..."
...Helicases, such as UvrD, RecQ, BLM, T4 and T7 helicases (Dessinges et al., 2004; Johnson et al., 2007; Klaue et al., 2013; Lionnet et al., 2007; Sun et al., 2008; Wang et al., 2015), have also been reported to switch strand during unwinding to translocate in a reverse direction, away from the DNA fork instead of moving toward it, such that a reannealing fork follows behind the helicase (Figure 3C)....
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...Helicases, such as UvrD, RecQ, BLM, T4 and T7 helicases (Dessinges et al., 2004; Johnson et al., 2007; Klaue et al., 2013; Lionnet et al., 2007; Sun et al., 2008; Wang et al., 2015), have also been reported to switch strand during unwinding to translocate in a reverse direction, away from the DNA…...
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...Helicase slippage was also observed with other ring-shaped replicative helicases (Klaue et al., 2013; Lee et al., 2014; Manosas et al., 2012b)....
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References
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TL;DR: This review sets out to define a nomenclature for helicase and translocase enzymes based on current knowledge of sequence, structure, and mechanism, and delineate six superfamilies of enzymes, with examples of crystal structures where available.
Abstract: Helicases and translocases are a ubiquitous, highly diverse group of proteins that perform an extraordinary variety of functions in cells. Consequently, this review sets out to define a nomenclature for these enzymes based on current knowledge of sequence, structure, and mechanism. Using previous definitions of helicase families as a basis, we delineate six superfamilies of enzymes, with examples of crystal structures where available, and discuss these structures in the context of biochemical data to outline our present understanding of helicase and translocase activity. As a result, each superfamily is subdivided, where appropriate, on the basis of mechanistic understanding, which we hope will provide a framework for classification of new superfamily members as they are discovered and characterized.
1,145 citations
TL;DR: Two different structures of PcrA DNA helicase complexed with the same single strand tailed DNA duplex are determined, providing snapshots of different steps on the catalytic pathway, providing evidence against an "active rolling" model for helicase action but are instead consistent with an "inchworm" mechanism.
759 citations
TL;DR: The structure of the HCV NS3 RNA helicase domain complexed with a single-stranded DNA oligonucleotide has been solved to 2.2 A resolution and is a member of a superfamily of helicases, termed superfamily II.
630 citations
TL;DR: This Review discusses how these proteins might suppress genomic rearrangements, and therefore function as 'caretaker' tumour suppressors.
Abstract: Around 1% of the open reading frames in the human genome encode predicted DNA and RNA helicases. One highly conserved group of DNA helicases is the RecQ family. Genetic defects in three of the five human RecQ helicases, BLM, WRN and RECQ4, give rise to defined syndromes associated with cancer predisposition, some features of premature ageing and chromosomal instability. In recent years, there has been a tremendous advance in our understanding of the cellular functions of individual RecQ helicases. In this Review, we discuss how these proteins might suppress genomic rearrangements, and therefore function as 'caretaker' tumour suppressors.
432 citations
TL;DR: A series of crystal structures of the UvrD helicase complexed with DNA and ATP hydrolysis intermediates reveal that ATP binding alone leads to unwinding of 1 base pair by directional rotation and translation of the DNA duplex, and ADP and Pi release leads to translocation of the developing single strand.
338 citations