Ulrich F. Keyser

Single-molecule quantification of the strength and sequence specificity of interactions between proteins and nucleic acids would facilitate the probing of protein–DNA binding. Here we show that binding events between the catalytically inactive Cas9 ribonucleoprotein and any pre-defined short sequence of double-stranded DNA can be identified by sensing changes in ionic current as suitably designed barcoded linear DNA nanostructures with Cas9-binding double-stranded DNA overhangs translocate through solid-state nanopores. We designed barcoded DNA nanostructures to study the relationships between DNA sequence and the DNA-binding specificity, DNA-binding efficiency and DNA-mismatch tolerance of Cas9 at the single-nucleotide level. Nanopore-based sensing of DNA-barcoded nanostructures may help to improve the design of efficient and specific ribonucleoproteins for biomedical applications …

Transcription, a critical process in molecular biology, has found many applications in RNA synthesis, including mRNA vaccines and RNA therapeutics. However, current RNA characterization technologies suffer from amplification and enzymatic biases that lead to loss of native information. Here, we introduce a strategy to quantitatively study both transcription and RNA polymerase behaviour by sizing RNA with RNA nanotechnology and nanopores. To begin, we utilize T7 RNA polymerase to transcribe linear DNA lacking termination sequences. Surprisingly, we discover alternative transcription termination in the origin of replication sequence. Next, we employ circular DNA without transcription terminators to perform rolling circle transcription. This allows us to gain valuable insights into the processivity and transcription behaviour of RNA polymerase at the single-molecule level. Our work demonstrates how RNA …

Recent experiments have probed the relative likelihoods of trajectories in stochastic systems by observing survival probabilities within a tube of radius in spacetime. We measure such probabilities here for a colloidal particle in a corrugated channel, corresponding to a bistable potential with state-dependent diffusivity. In contrast to previous findings for state-independent noise, we find that the most probable pathway changes qualitatively as the tube radius is altered. We explain this by computing the survival probabilities predicted by overdamped Langevin dynamics. At high enough resolution (small enough ), survival probabilities depend solely on diffusivity variations, independent of deterministic forces; finite corrections yield a generalization of the Onsager-Machlup action. As corollary, ratios of survival probabilities are singular as , but become regular, and described by the classical Onsager-Machlup action, only in the special case of state-independent noise.

Supplementary Figure 1. Design of RNA ID. a The position of the repeats label ‘R’and the ‘1’bits within the RNA ID is shown. b ‘R’represents a DNA CAG10 oligonucleotide (docking strand) that binds to the CUG repeats, this oligo has an overhang sequence with 3’biotin that binds to a complementary strand (imaging strand) with another 3’biotin, enabling the overall binding of two monovalent streptavidins to RNA ID. c The RNA ID is decorated with ‘1’. Two ‘1’bits are included in the RNA ID design to produce a distinguishable signal.‘1’bits lack biotin on the docking strand, which enables the binding of only one monovalent streptavidin per bit, providing a discriminatory signal in nanopore recordings.

Author Correction: Sensing the DNA-mismatch tolerance of catalytically inactive Cas9 via barcoded DNA nanostructures in solid-state nanopores - PMC Back to Top Skip to main content NIH NLM Logo Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now. Search PMC Full-Text Archive Search in PMC Advanced Search User Guide Journal List Nature Portfolio PMC10963258 Other Formats PDF (499K) Actions Cite Collections Share Permalink Copy RESOURCES Similar articles Cited by other articles Links to NCBI Databases Journal List Nature Portfolio PMC10963258 As a library, NLM provides access to scientific literature. Inclusion in an NLM database does not imply endorsement of, or agreement with, the contents by NLM or the National Institutes of Health. Learn more: PMC Disclaimer …

Multiplexed nucleic acid sensing methods with high specificity are vital for clinical diagnostics and infectious disease control, especially in the postpandemic era. Nanopore sensing techniques have developed in the past two decades, offering versatile tools for biosensing while enabling highly sensitive analyte measurements at the single-molecule level. Here, we establish a nanopore sensor based on DNA dumbbell nanoswitches for multiplexed nucleic acid detection and bacterial identification. The DNA nanotechnology-based sensor switches from an “open” into a “closed” state when a target strand hybridizes to two sequence-specific sensing overhangs. The loop in the DNA pulls two groups of dumbbells together. The change in topology results in an easily recognized peak in the current trace. Simultaneous detection of four different sequences was achieved by assembling four DNA dumbbell nanoswitches on …

Respiratory infections are the major cause of death from infectious disease worldwide. Multiplexed diagnostic approaches are essential as many respiratory viruses have indistinguishable symptoms. We created self-assembled DNA nanobait that can simultaneously identify multiple short RNA targets. The nanobait approach relies on specific target selection via toehold-mediated strand displacement and rapid readout via nanopore sensing. Here we show that this platform can concurrently identify several common respiratory viruses, detecting a panel of short targets of viral nucleic acids from multiple viruses. Our nanobait can be easily reprogrammed to discriminate viral variants with single-nucleotide resolution, as we demonstrated for several key SARS-CoV-2 variants. Last, we show that the nanobait discriminates between samples extracted from oropharyngeal swabs from negative- and positive-SARS-CoV-2 …

Electrophoretic transport plays a pivotal role in advancing sensing technologies, with A-form nucleic acids, predominantly RNA-containing, emerging as the new frontier for nanopore sensing and sequencing. Here, we compare the less-explored dynamics of A-form electrophoretic transport with the well-researched transport of B-form DNA. Using DNA/RNA nanotechnology and solid-state nanopores, the translocation of RNA: DNA (RD) and DNA: DNA (DD) duplexes was examined. Notably, RD duplexes were found to translocate through nanopores up to 1.8 times faster than DD duplexes, despite containing the same number of base pairs. Our experiments reveal that A-and B-form duplex molecules with the same contour length move with comparable velocity through nanopores. We examined the physical characteristics of both duplex forms using atomic force microscopy, agarose gel electrophoresis, and dynamic …

The source data is presented in excel files. Excel, Origin Pro or Python can be used to analyse the data. Agarose gels are included and they can be analysed in ImageJ.

An approach relying on nanocavity confinement is developed in this paper for the sizing of nanoscale particles and single biomolecules in solution. The approach, termed nanocavity diffusional sizing (NDS), measures particle residence times within nanofluidic cavities to determine their hydrodynamic radii. Using theoretical modeling and simulations, we show that the residence time of particles within nanocavities above a critical time scale depends on the diffusion coefficient of the particle, which allows the estimation of the particle’s size. We demonstrate this approach experimentally through the measurement of particle residence times within nanofluidic cavities using single-molecule confocal microscopy. Our data show that the residence times scale linearly with the sizes of nanoscale colloids, protein aggregates, and single DNA oligonucleotides. NDS thus constitutes a new single molecule optofluidic approach …

This is the source data for Nanopore sensing with DNA nanostructures reveals Guide-Intrinsic Mismatch Tolerance of CRISPR/dCas9 in Nature Biomedical Engineering. The data was generated by mixing a DNA nanostructure with dCas9 and measuring the change in current generated from translocation in solid-state nanopores. Data is originally in TDMS format (which can be given upon request) and then converted from TDMS to hdf5 using https://bitbucket. org/nikaer/nanopyre/src/master/-from this translocationfinder is used which writes files from TDMS (labview) to hdf5. Processing and further data analysis from the hdf5 is done using https://github. com/sarahsandler/nanopro. TDMS files are from labview, however there is a nptdms software which can be used to read them into python. Please see the manuscript for more details.

In current nanopore-based label-free single-molecule sensing technologies, stochastic processes influence the selection of translocating molecule, translocation rate and translocation velocity. As a result, single-molecule translocations are challenging to control both spatially and temporally. Here we present a method using a glass nanopore mounted on a three-dimensional nanopositioner to spatially select molecules, deterministically tethered on a glass surface, for controlled translocations. By controlling the distance between the nanopore and glass surface, we can actively select the region of interest on the molecule and scan it a controlled number of times and at a controlled velocity. Decreasing the velocity and averaging thousands of consecutive readings of the same molecule increases the signal-to-noise ratio by two orders of magnitude compared with free translocations. We demonstrate the method’s …

Nanopore analysis relies on ensemble averaging of translocation signals obtained from numerous molecules, requiring a relatively high sample concentration and a long turnaround time from the sample to results. The recapture and subsequent re-reading of the same molecule is a promising alternative that enriches the signal information from a single molecule. Here, we describe how an asymmetric nanopore improves molecular ping-pong by promoting the recapture of the molecule in the trans reservoir. We also demonstrate that the molecular recapture could be improved by linking the target molecule to a long DNA carrier to reduce the diffusion, thereby achieving over 100 recapture events. Using this ping-pong methodology, we demonstrate its use in accurately resolving nanostructure motifs along a DNA scaffold through repeated detection. Our method offers novel insights into the control of DNA polymer dynamics within nanopore confinement and opens avenues for the development of a high-fidelity DNA detection platform.

Dendrites and dendritic spines are the essential cellular compartments in neuronal communication, conveying information through transient voltage signals. Our understanding of these compartmentalized voltage dynamics in fine, distal neuronal dendrites remains poor due to the difficulties inherent to accessing and stably recording from such small, nanoscale cellular compartments for a sustained time. To overcome these challenges, we use nanopipettes that permit long and stable recordings directly from fine neuronal dendrites. We reveal a diversity of voltage dynamics present locally in dendrites, such as spontaneous voltage transients, bursting events and oscillating periods of silence and firing activity, all of which we characterized using segmentation analysis. Remarkably, we find that neuronal dendrites can display spontaneous hyperpolarisation events, and sustain transient hyperpolarised states. The …

Sequence-specific interactions between nucleic acids and proteins are fundamental to many critical biological processes. Despite the ubiquitous nature of protein-DNA binding, versatile methods to probe the specificity of these events remain elusive. In particular, single-molecule methods that enable the quantification of these processes are essential towards understanding and manipulating protein binding. To this end, we report a system which leverages solid state nanopores with diameters of~ 10 nm to identify binding events between DNA and CRISPR associated (Cas) probes–specifically catalytically inactive or dead Cas9 (dCas9), which binds to DNA but does not cleave it. The rational design of DNA nanostructures allows for the incorporation of user-defined binding sequences, enabling a systematic study of how mismatch position and identity impacts the binding efficiency. These experiments reveal the relationship between sequence and binding at the single nucleotide level, exemplifying the utility of both nanopore measurements and DNA nanotechnology towards the next generation of biosensing assays.

Nanopores have developed into powerful single-molecule sensors capable of identifying and characterizing small polymers, such as DNA, by electrophoretically driving them through a nanoscale pore and monitoring temporary blockades in the ionic pore current. However, the relationship between nanopore signals and the physical properties of DNA remains only partly understood. Herein, we introduce a programmable DNA carrier platform to capture carefully designed DNA nanostructures. Controlled translocation experiments through our glass nanopores allowed us to disentangle this relationship. We vary DNA topology by changing the length, strand duplications, sequence, unpaired nucleotides, and rigidity of the analyte DNA and find that the ionic current drop is mainly determined by the volume and flexibility of the DNA nanostructure in the nanopore. Finally, we use our understanding of the role of DNA …

Misfolded protein oligomers are of central importance in both the diagnosis and treatment of Alzheimer’s and Parkinson’s diseases. However, accurate high-throughput methods to detect and quantify oligomer populations are still needed. We present here a single-molecule approach for the detection and quantification of oligomeric species. The approach is based on the use of solid-state nanopores and multiplexed DNA barcoding to identify and characterize oligomers from multiple samples. We study α-synuclein oligomers in the presence of several small-molecule inhibitors of α-synuclein aggregation as an illustration of the potential applicability of this method to the development of diagnostic and therapeutic methods for Parkinson’s disease.

Most animal cells are surrounded by a cell membrane and an underlying actomyosin cortex. Both structures are linked, and they are under tension. In-plane membrane tension and cortical tension both influence many cellular processes, including cell migration, division, and endocytosis. However, while actomyosin tension is regulated by substrate stiffness, how membrane tension responds to mechanical substrate properties is currently poorly understood. Here, we probed the effective membrane tension of neurons and fibroblasts cultured on glass and polyacrylamide substrates of varying stiffness using optical tweezers. In contrast to actomyosin-based traction forces, both peak forces and steady-state tether forces of cells cultured on hydrogels were independent of substrate stiffness and did not change after blocking myosin II activity using blebbistatin, indicating that tether and traction forces are not directly …

The present invention provides compositions and methods for transferring phospholipids and other molecules between the leaflets of a cell membrane. The compositions comprise at least one nucleic acid or compound having a hydrophilic region, where the composition is able to form a nanostructure that forms a toroidal pore in a lipid membrane. The nucleic acid or hydrophilic region-containing compound further contains an attached molecule capable of inserting the nanostructure into the lipid membrane. The invention also provides methods for scrambling lipids and other molecules in a cell membrane, which can be used to alter the function of a selected cell or to facilitate the death of the cell. The scrambling activity of synthetic scramblases described herein outperforms previously known enzymatically active DNA nanostructures and naturally occurring scramblases, in some cases by several orders of magnitude.

Developing highly enhanced plasmonic nanocavities allows direct observation of light–matter interactions at the nanoscale. With DNA origami, the ability to precisely nanoposition single-quantum emitters in ultranarrow plasmonic gaps enables detailed study of their modified light emission. By developing protocols for creating nanoparticle-on-mirror constructs in which DNA nanostructures act as reliable and customizable spacers for nanoparticle binding, we reveal that the simple picture of Purcell-enhanced molecular dye emission is misleading. Instead, we show that the enhanced dipolar dye polarizability greatly amplifies optical forces acting on the facet Au atoms, leading to their rapid destabilization. Using different dyes, we find that emission spectra are dominated by inelastic (Raman) scattering from molecules and metals, instead of fluorescence, with molecular bleaching also not evident despite the large …