Single-Molecule Mechanical Unfolding of AT-Rich Chromosomal Fragile Site DNA Hairpins: Resolving the Thermodynamic and Kinetic Effects of a Single G-T Mismatch

2020 ◽  
Vol 124 (42) ◽  
pp. 9365-9370
Author(s):  
Xiong Li ◽  
Yufeng Pei ◽  
Yashuo Zhang ◽  
Yajun Liu ◽  
Wenhao Fu ◽  
...  
Keyword(s):  
Single Molecule ◽  
Fragile Site ◽  
Dna Hairpins ◽  
Kinetic Effects

Conformational Dynamics of DNA Hairpins at Millisecond Resolution Obtained from Analysis of Single-Molecule FRET Histograms

2013 ◽  
Vol 117 (50) ◽  
pp. 16105-16109 ◽  
Author(s):  
Roman Tsukanov ◽  
Toma E. Tomov ◽  
Yaron Berger ◽  
Miran Liber ◽  
Eyal Nir
Keyword(s):  
Single Molecule ◽  
Conformational Dynamics ◽  
Dna Hairpins ◽  
Single Molecule Fret

scholarly journals Salt Effects on the Thermodynamics of a Frameshifting RNA Pseudoknot under Tension

2016 ◽  
Author(s):  
Naoto Hori ◽  
Natalia A. Denesyuk ◽  
D. Thirumalai
Keyword(s):  
Single Molecule ◽  
Interaction Coefficient ◽  
Critical Force ◽  
Coarse Grained ◽  
Stem Loop ◽  
Ribosomal Frameshifting ◽  
Dna Hairpins ◽  
Coarse Grained Simulations ◽  
The Stability ◽  
Rna Interaction

Because of the potential link between -1 programmed ribosomal frameshifting and response of a pseudoknot (PK) RNA to force, a number of single molecule pulling experiments have been performed on PKs to decipher the mechanism of programmed ribosomal frameshifting. Motivated in part by these experiments, we performed simulations using a coarse-grained model of RNA to describe the response of a PK over a range of mechanical forces (fs) and monovalent salt concentrations (Cs). The coarse-grained simulations quantitatively reproduce the multistep thermal melting observed in experiments, thus validating our model. The free energy changes obtained in simulations are in excellent agreement with experiments. By varying f and C, we calculated the phase diagram that shows a sequence of structural transitions, populating distinct intermediate states. As f and C are changed, the stem-loop tertiary interactions rupture first, followed by unfolding of the 3’-end hairpin (I⇌F). Finally, the 5’-end hairpin unravels, producing an extended state (E⇌I). A theoretical analysis of the phase boundaries shows that the critical force for rupture scales as (log Cm)α with α = 1 (0.5) for E⇌I (I⇌F) transition. This relation is used to obtain the preferential ion-RNA interaction coefficient, which can be quantitatively measured in single-molecule experiments, as done previously for DNA hairpins. A by-product of our work is the suggestion that the frameshift efficiency is likely determined by the stability of the 5’ end hairpin that the ribosome first encounters during translation.

scholarly journals Dynamics of strand slippage in DNA hairpins formed by CAG repeats: roles of sequence parity and trinucleotide interrupts

2020 ◽  
Vol 48 (5) ◽  
pp. 2232-2245 ◽  
Author(s):  
Pengning Xu ◽  
Feng Pan ◽  
Christopher Roland ◽  
Celeste Sagui ◽  
Keith Weninger
Keyword(s):  
Molecular Dynamics ◽  
Single Molecule ◽  
Neurodegenerative Disorders ◽  
Atomic Level ◽  
Trinucleotide Repeats ◽  
Cag Repeats ◽  
Dna Hairpins ◽  
Disease Phenotypes ◽  
Single Molecule Fret ◽  
Insight Into

Abstract DNA trinucleotide repeats (TRs) can exhibit dynamic expansions by integer numbers of trinucleotides that lead to neurodegenerative disorders. Strand slipped hairpins during DNA replication, repair and/or recombination may contribute to TR expansion. Here, we combine single-molecule FRET experiments and molecular dynamics studies to elucidate slipping dynamics and conformations of (CAG)n TR hairpins. We directly resolve slipping by predominantly two CAG units. The slipping kinetics depends on the even/odd repeat parity. The populated states suggest greater stability for 5′-AGCA-3′ tetraloops, compared with alternative 5′-CAG-3′ triloops. To accommodate the tetraloop, even(odd)-numbered repeats have an even(odd) number of hanging bases in the hairpin stem. In particular, a paired-end tetraloop (no hanging TR) is stable in (CAG)n = even, but such situation cannot occur in (CAG)n = odd, where the hairpin is “frustrated’’ and slips back and forth between states with one TR hanging at the 5′ or 3′ end. Trinucleotide interrupts in the repeating CAG pattern associated with altered disease phenotypes select for specific conformers with favorable loop sequences. Molecular dynamics provide atomic-level insight into the loop configurations. Reducing strand slipping in TR hairpins by sequence interruptions at the loop suggests disease-associated variations impact expansion mechanisms at the level of slipped hairpins.

scholarly journals Reconstructing folding energy landscapes from splitting probability analysis of single-molecule trajectories

2015 ◽  
Vol 112 (23) ◽  
pp. 7183-7188 ◽  
Author(s):  
Ajay P. Manuel ◽  
John Lambert ◽  
Michael T. Woodside
Keyword(s):  
Single Molecule ◽  
Self Assembly ◽  
Energy State ◽  
Energy Landscape ◽  
Minimum Energy ◽  
Reaction Coordinate ◽  
Folding Energy ◽  
Energy Landscapes ◽  
Simple Method ◽  
Dna Hairpins

Structural self-assembly in biopolymers, such as proteins and nucleic acids, involves a diffusive search for the minimum-energy state in a conformational free-energy landscape. The likelihood of folding proceeding to completion, as a function of the reaction coordinate used to monitor the transition, can be described by the splitting probability, pfold(x). Pfold encodes information about the underlying energy landscape, and it is often used to judge the quality of the reaction coordinate. Here, we show how pfold can be used to reconstruct energy landscapes from single-molecule folding trajectories, using force spectroscopy measurements of single DNA hairpins. Calculating pfold(x) directly from trajectories of the molecular extension measured for hairpins fluctuating in equilibrium between folded and unfolded states, we inverted the result expected from diffusion over a 1D energy landscape to obtain the implied landscape profile. The results agreed well with the landscapes reconstructed by established methods, but, remarkably, without the need to deconvolve instrumental effects on the landscape, such as tether compliance. The same approach was also applied to hairpins with multistate folding pathways. The relative insensitivity of the method to the instrumental compliance was confirmed by simulations of folding measured with different tether stiffnesses. This work confirms that the molecular extension is a good reaction coordinate for these measurements, and validates a powerful yet simple method for reconstructing landscapes from single-molecule trajectories.

scholarly journals Submicrometer elasticity of double-stranded DNA revealed by precision force-extension measurements with magnetic tweezers

2019 ◽  
Vol 5 (6) ◽  
pp. eaav1697 ◽  
Author(s):  
Min Ju Shon ◽  
Sang-Hyun Rah ◽  
Tae-Young Yoon
Keyword(s):  
Single Molecule ◽  
Persistence Length ◽  
Gc Content ◽  
Magnetic Tweezers ◽  
Force Variability ◽  
Chain Model ◽  
Force Extension ◽  
Dna Hairpins ◽  
Double Stranded Dna ◽  
Order Of Magnitude

Submicrometer elasticity of double-stranded DNA (dsDNA) governs nanoscale bending of DNA segments and their interactions with proteins. Single-molecule force spectroscopy, including magnetic tweezers (MTs), is an important tool for studying DNA mechanics. However, its application to short DNAs under 1 μm is limited. We developed an MT-based method for precise force-extension measurements in the 100-nm regime that enables in situ correction of the error in DNA extension measurement, and normalizes the force variability across beads by exploiting DNA hairpins. The method reduces the lower limit of tractable dsDNA length down to 198 base pairs (bp) (67 nm), an order-of-magnitude improvement compared to conventional tweezing experiments. Applying this method and the finite worm-like chain model we observed an essentially constant persistence length across the chain lengths studied (198 bp to 10 kbp), which steeply depended on GC content and methylation. This finding suggests a potential sequence-dependent mechanism for short-DNA elasticity.

scholarly journals Extracting Kinetics from Single-Molecule Force Spectroscopy: Nanopore Unzipping of DNA Hairpins

2007 ◽  
Vol 92 (12) ◽  
pp. 4188-4195 ◽  
Author(s):  
Olga K. Dudko ◽  
Jérôme Mathé ◽  
Attila Szabo ◽  
Amit Meller ◽  
Gerhard Hummer
Keyword(s):  
Single Molecule ◽  
Force Spectroscopy ◽  
Single Molecule Force Spectroscopy ◽  
Dna Hairpins

scholarly journals Removal of Covalent Heterogeneity Reveals Simple Folding Behavior for P4-P6 RNA

2011 ◽  
Vol 286 (22) ◽  
pp. 19872-19879 ◽  
Author(s):  
Max Greenfeld ◽  
Sergey V. Solomatin ◽  
Daniel Herschlag
Keyword(s):  
Single Molecule ◽  
Rna Folding ◽  
Tertiary Structure ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Molecular Heterogeneity ◽  
Group I ◽  
Single Molecule Studies ◽  
Covalent Modifications ◽  
Kinetic Effects

RNA folding landscapes have been described alternately as simple and as complex. The limited diversity of RNA residues and the ability of RNA to form stable secondary structures prior to adoption of a tertiary structure would appear to simplify folding relative to proteins. Nevertheless, there is considerable evidence for long-lived misfolded RNA states, and these observations have suggested rugged energy landscapes. Recently, single molecule fluorescence resonance energy transfer (smFRET) studies have exposed heterogeneity in many RNAs, consistent with deeply furrowed rugged landscapes. We turned to an RNA of intermediate complexity, the P4-P6 domain from the Tetrahymena group I intron, to address basic questions in RNA folding. P4-P6 exhibited long-lived heterogeneity in smFRET experiments, but the inability to observe exchange in the behavior of individual molecules led us to probe whether there was a non-conformational origin to this heterogeneity. We determined that routine protocols in RNA preparation and purification, including UV shadowing and heat annealing, cause covalent modifications that alter folding behavior. By taking measures to avoid these treatments and by purifying away damaged P4-P6 molecules, we obtained a population of P4-P6 that gave near-uniform behavior in single molecule studies. Thus, the folding landscape of P4-P6 lacks multiple deep furrows that would trap different P4-P6 molecules in different conformations and contrasts with the molecular heterogeneity that has been seen in many smFRET studies of structured RNAs. The simplicity of P4-P6 allowed us to reliably determine the thermodynamic and kinetic effects of metal ions on folding and to now begin to build more detailed models for RNA folding behavior.

The method of replication affects metal film granularity and resolution

1989 ◽  
Vol 47 ◽  
pp. 708-709
Author(s):  
George C. Ruben
Keyword(s):  
Electron Beam ◽  
High Resolution ◽  
Film Thickness ◽  
Single Molecule ◽  
Metal Film ◽  
Vertical Surface ◽  
High Resolution Imaging ◽  
Controllable Factors ◽  
Resolution Imaging

Single molecule resolution in electron beam sensitive, uncoated, noncrystalline materials has been impossible except in thin Pt-C replicas ≤ 150Å) which are resistant to the electron beam destruction. Previously the granularity of metal film replicas limited their resolution to ≥ 20Å. This paper demonstrates that Pt-C film granularity and resolution are a function of the method of replication and other controllable factors. Low angle 20° rotary , 45° unidirectional and vertical 9.7±1 Å Pt-C films deposited on mica under the same conditions were compared in Fig. 1. Vertical replication had a 5A granularity (Fig. 1c), the highest resolution (table), and coated the whole surface. 45° replication had a 9Å granulartiy (Fig. 1b), a slightly poorer resolution (table) and did not coat the whole surface. 20° rotary replication was unsuitable for high resolution imaging with 20-25Å granularity (Fig. 1a) and resolution 2-3 times poorer (table). Resolution is defined here as the greatest distance for which the metal coat on two opposing faces just grow together, that is, two times the apparent film thickness on a single vertical surface.

Single molecule optical diffraction: A tool for understanding the structure of triple stranded left-hand helical cellulose

1989 ◽  
Vol 47 ◽  
pp. 1024-1025
Author(s):  
George C. Ruben ◽  
William Krakow
Keyword(s):  
Single Molecule ◽  
Helical Structure ◽  
Optical Diffraction ◽  
Maximum Diameter ◽  
Primary Cell Wall ◽  
Cellulose Synthesis ◽  
Left Hand ◽  
Left Handed ◽  
Freeze Dried ◽  
Diffraction Patterns

Tobacco primary cell wall and normal bacterial Acetobacter xylinum cellulose formation produced a 36.8±3Å triple-stranded left-hand helical microfibril in freeze-dried Pt-C replicas and in negatively stained preparations for TEM. As three submicrofibril strands exit the wall of Axylinum , they twist together to form a left-hand helical microfibril. This process is driven by the left-hand helical structure of the submicrofibril and by cellulose synthesis. That is, as the submicrofibril is elongating at the wall, it is also being left-hand twisted and twisted together with two other submicrofibrils. The submicrofibril appears to have the dimensions of a nine (l-4)-ß-D-glucan parallel chain crystalline unit whose long, 23Å, and short, 19Å, diagonals form major and minor left-handed axial surface ridges every 36Å.The computer generated optical diffraction of this model and its corresponding image have been compared. The submicrofibril model was used to construct a microfibril model. This model and corresponding microfibril images have also been optically diffracted and comparedIn this paper we compare two less complex microfibril models. The first model (Fig. 1a) is constructed with cylindrical submicrofibrils. The second model (Fig. 2a) is also constructed with three submicrofibrils but with a single 23 Å diagonal, projecting from a rounded cross section and left-hand helically twisted, with a 36Å repeat, similar to the original model (45°±10° crossover angle). The submicrofibrils cross the microfibril axis at roughly a 45°±10° angle, the same crossover angle observed in microflbril TEM images. These models were constructed so that the maximum diameter of the submicrofibrils was 23Å and the overall microfibril diameters were similar to Pt-C coated image diameters of ∼50Å and not the actual diameter of 36.5Å. The methods for computing optical diffraction patterns have been published before.

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