…who joined the group for an 6 week internship (Andreas) and a short capita selecta (Hans). Andreas will try unifying some fragmented software packages for in vivo single particle tracking. Hans will push the limits of our ultrafast pSMLM algorithm for super-resolution microscopy.
, bioRxiv, 2018 [
DNA-binding proteins utilise different recognition mechanisms to locate their DNA targets. Some proteins recognise specific nucleotide sequences, while many DNA repair proteins interact with specific (often bent) DNA structures. While sequence-specific DNA binding mechanisms have been studied extensively, structure-specific mechanisms remain unclear. Here, we study structure-specific DNA recognition by examining the structure and dynamics of DNA polymerase I (Pol) substrates both alone and in Pol-DNA complexes. Using a rigid-body docking approach based on a network of 73 distance restraints collected using single-molecule FRET, we determined a novel solution structure of the singlenucleotide-gapped DNA-Pol binary complex. The structure was highly consistent with previous crystal structures with regards to the downstream primer-template DNA substrate; further, our structure showed a previously unobserved sharp bend (~120°) in the DNA substrate; we also showed that this pronounced bending of the substrate is present in living bacteria. All-atom molecular dynamics simulations and single-molecule quenching assays revealed that 4-5 nt of downstream gap-proximal DNA are unwound in the binary complex. Coarse-grained simulations on free gapped substrates reproduced our experimental FRET values with remarkable accuracy ( = -0.0025 across 34 independent distances) and revealed that the one-nucleotide-gapped DNA frequently adopted highly bent conformations similar to those in the Pol-bound state (ΔG 7 kT) or duplex (>> 10 kT) DNA. Our results suggest a mechanism by which Pol and other structure-specific DNA-binding proteins locate their DNA targets through sensing of the conformational dynamics of DNA substrates.
Good news! The proposal “LocalBioFood: Localisation of bio-macromolecules in food matrices” submitted by Ilja Voets (TU/e) and our lab has been granted by the NWO innovation fund for chemistry [link].
Within the project, the three appointed PhD students will image different components in food, like proteins and carbohydrates, on a sub 100nm length scale using advanced fluorescence microscopy. The project is a collaboration between Eindhoven University of Technology, Wageningen University, Confocal.nl, Unilever and DSM.
, , , , 2018, [
We present a fast and model-free 2D and 3D single-molecule localization algorithm that allows more than 3 million localizations per second on a standard multi-core CPU with localization accuracies in line with the most accurate algorithms currently available. Our algorithm converts the region of interest around a point spread function (PSF) to two phase vectors (phasors) by calculating the first Fourier coefficients in both x- and y-direction. The angles of these phasors are used to localize the center of the single fluorescent emitter, and the ratio of the magnitudes of the two phasors is a measure for astigmatism, which can be used to obtain depth information (z-direction). Our approach can be used both as a stand-alone algorithm for maximizing localization speed and as a first estimator for more time consuming iterative algorithms.
For the latest software implementation into thunderSTORM, please follow the [link].
, 2017, [
Single-molecule detection schemes offer powerful means to overcome static and dynamic heterogeneity inherent to complex samples. Probing chemical and biological interactions and reactions with high throughput and time resolution, however, remains challenging and often requires surface-immobilized entities. Here, utilizing camera-based fluorescence microscopy, we present glass-made nanofluidic devices in which fluorescently labelled molecules flow through nanochannels that confine their diffusional movement. The first design features an array of parallel nanochannels for high-throughput analysis of molecular species under equilibrium conditions allowing us to record 200.000 individual localization events in just 10 minutes. Using these localizations for single particle tracking, we were able to obtain accurate flow profiles including flow speeds and diffusion coefficients inside the channels. A second design featuring a T-shaped nanochannel enables precise mixing of two different species as well as the continuous observation of chemical reactions. We utilized the design to visualize enzymatically driven DNA synthesis in real time and at the single-molecule level. Based on our results, we are convinced that the versatility and performance of the nanofluidic devices will enable numerous applications in the life sciences.
…who joins the group for his MSc thesis. In collaboration with Dr. Klaus Mathwig (Pharmacy, Groningen), Dr. Peter van Baarlen (Host-Microbe Interactions, Wageningen) and Simon van der Els (NIZO food research and HMI, Wageningen), he will work towards monitoring bacterial conjugation in real time and at the single-cell level.
K. Mathwig, C. Fijen, M. Fontana, S. G. Lemay and J. Hohlbein, Procedia Technology, 27, 141, 2017, [link]
We introduce a nanofluidicmixing device
entirely fabricated in glass for the fluorescence detection of single molecules. The design consists of a nanochannel T-junction and allows the continuous monitoring of chemical or enzymatic reactions of analytes as they arrive from two independent inlets. The fluorescently labeled molecules are tracked before, during and after they enter the mixing region, and their reactions with each other are observed by means of optical readout such as Förster Resonance Energy Transfer (FRET). Our method can be used for analyzing the kinetics of DNA annealing in a high-parallelized fashion.