Mechanism of Disruption of the Amt-GlnK Complex by PII-Mediated Sensing of 2-Oxoglutarate

GlnK proteins regulate the active uptake of ammonium by Amt transport proteins by inserting their regulatory T-loops into the transport channels of the Amt trimer and physically blocking substrate passage. They sense the cellular nitrogen status through 2-oxoglutarate, and the energy level of the cell by binding both ATP and ADP with different affinities. The hyperthermophilic euryarchaeon Archaeoglobus fulgidus possesses three Amt proteins, each encoded in an operon with a GlnK ortholog. One of these proteins, GlnK2 was recently found to be incapable of binding 2-OG, and in order to understand the implications of this finding we conducted a detailed structural and functional analysis of a second GlnK protein from A. fulgidus, GlnK3. Contrary to Af-GlnK2 this protein was able to bind both ATP/2-OG and ADP to yield inactive and functional states, respectively. Due to the thermostable nature of the protein we could observe the exact positioning of the notoriously flexible T-loops and explain the binding behavior of GlnK proteins to their interaction partner, the Amt proteins. A thermodynamic analysis of these binding events using microcalorimetry evaluated by microstate modeling revealed significant differences in binding cooperativity compared to other characterized PII proteins, underlining the diversity and adaptability of this class of regulatory signaling proteins

WTZ Russland: Kooperation mit der AdW Moskau in der Lasermedizin auf den Gebieten Strahlfuehrung, neue Laserkonzepte sowie Diagnostik und Dosimetrie im Rahmen des WTZ mit der UdSSR

Available from TIB Hannover: F94B1380+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Correlative Single-Molecule FRET and DNA-PAINT Imaging

DNA-PAINT is an optical super-resolution microscopy method that can visualize nanoscale protein arrangements and provide spectrally unlimited multiplexing capabilities. However, current multiplexing implementations based on, for example, DNA exchange (such as Exchange-PAINT) achieves multitarget detection by sequential imaging, limiting throughput. Here, we combine DNA-PAINT with single-molecule FRET and use the FRET efficiency as parameter for multiplexed imaging with high specificity. We demonstrate correlated single-molecule FRET and super resolution on DNA origami structures, which are equipped with binding sequences that are targeted by pairs of dye-labeled oligonucleotides generating the FRET signal. We hither extract FRET values from single binding sites that are spaced just similar to 55 nm apart, demonstrating super-resolution FRET imaging. This combination of FRET and DNA-PAINT allows for multiplexed super-resolution imaging with low background and opens the door for accurate distance readout in the 1-10 nm range

EXOMIO virtual simulation ; oropharynx , prostate and breast cancers

Simulators are medical devices used in the oncology clinics to perform the simulation for the external beam radiotherapy treatment. Unlikely for a clinic to obtain a real Simulator is a high investment in terms of money, space and personnel. The alternative here can be a Virtual Simulator (VS). The CT simulators are system-software that can perform the simulation process using the Computed Tomography (CT) data set of the patient, including the external patient's skin landmarks, instead of the physical patient. In this paper we present a new high performance CT based virtual simulation system running on a low cost widely available PC hardware - EXOMIO. The implemented high-end visualization techniques allow the users to simulate every function of the real simulator including the mechanical component movements, radiation beam projection and fluoroscopy. Further more this virtual simulation concept provides the physicians with ergonomic volume definition and navigation tools. Our clinical experience is described using three patient examples: Neck cancer, prostate cancer and breast cancer. The advantages of virtual simulation system over classical simulation are stated and its clinical effectiveness is emphasized

Correlating DNA-PAINT and single-molecule FRET for multiplexed super-resolution imaging

Correlating DNA-PAINT (point accumulation for imaging in nanoscale topography) and single-molecule FRET (Forster resonance energy transfer) enables the multiplexed detection with sub-diffraction optical resolution. We designed pairs of short oligonucleotides, labeled with donor and acceptor fluorophores with various distances generating different FRET efficiencies. The strands can transiently bind to a target docking strand, simultaneous binding of both strands results in FRET signals which yield a super-resolved image via DNA-PAINT imaging. We demonstrate FRET-PAINT by designing and imaging DNA origami, which is a useful tool to establish super-resolution methods. The DNA origami structures were equipped with three target binding sites spaced by 55 nm, a sub-diffraction limited distance, however ensuring that no FRET between the target sites occurs. We resolved the individual binding sites in the donor and acceptor channels, and in addition extracted the FRET efficiency for each site in single and mixed populations. The combination of FRET and DNA-PAINT allows for multiplexed super-resolution imaging in conjunction with distance-sensitive readout in the 1 to 10 nm range

Quantification of membrane receptor complexes with single-molecule localization microscopy

Knowledge of assembly, subunit architecture and dynamics of membrane proteins in a cellular context is essential to infer their biological function. Optical super-resolution techniques provide the necessary spatial resolution to study these properties of membrane protein complexes in the context of their cellular environment. Single-molecule localization microscopy (SMLM) is particularly well suited, as next to high-resolution images, it provides quantitative information on the detection of single emitters. A challenge for current super-resolution methods is to resolve individual protein subunits within a densely packed protein cluster. For this purpose, we developed quantitative SMLM (qSMLM), which reports on molecular numbers by analyzing the kinetics of single emitter blinking. Next to theoretical models for various photophysical schemes, we demonstrate this method for a selection of fluorescent proteins and synthetic dyes and a selection of membrane proteins. We next applied this tool to toll-like receptor 4 (TLR4), and found a ligand-specific formation of monomeric or dimeric receptors. Next to fluorescent proteins, DNA-PAINT offers a novel and flexible approach for quantitative super-resolution microscopy. We demonstrate DNA-PAINT imaging of structurally defined DNA origami structures and robust quantification of target sites, as well as of membrane receptors. Molecular quantification, together with experiments following single receptor mobilities in live cells, will enlighten molecular mechanisms of receptor activation