Biology subjects

Hoess, P.

Publications and source records attributed to Hoess, P..

12 recordsLinked to original sources

bioRxiv2025

Continuum architecture dynamics of vesicle tethering in exocytosis

Essential for eukaryotic organisms, multiple copies of the exocyst complex tether each secretory vesicle to the plasma membrane (PM) in constitutive exocytosis. The exocyst higher-order structure (ExHOS) that coordinates the action of these multiple exocysts remains unexplored. We integrated particle-tracking, super-resolution microscopy and cryo-electron tomography in a model that time-resolves the continuum conformational landscape of the ExHOS and functionally annotates its different conformations. We found that 7 exocysts form flexible ring-shaped ExHOS that tether vesicles at <45 nm from the PM. The ExHOS, initially 19 nm in radius, rapidly expands while it pulls the vesicle towards the PM. Subsequently, the ExHOS stabilizes, securing the vesicle at [~]4 nm from the PM. After fusion, Sec18 mediates the ExHOS disassembly when its radius is 38 nm. By resolving the fundamental biophysical principles of tethering we bridged the gap between static isolated structures and the dynamic and multimeric nature of exocytosis.

cell biology↗

bioRxiv2022

Direct observation of motor protein stepping in living cells using MINFLUX

Dynamic measurements of molecular machines can provide invaluable insights into their mechanism, but have been challenging in living cells. Here, we developed live-cell tracking of single fluorophores with nanometer spatial and millisecond temporal resolution in 2D and 3D using the recently introduced super-resolution technique MINFLUX. This allowed us to resolve the precise stepping motion of the motor protein kinesin-1 as it walks on microtubules in living cells. In addition, nanoscopic tracking of motors on microtubule of fixed cells enabled us to resolve their spatial organization with protofilament resolution. Our approach will enable future in vivo studies of motor protein kinetics in complex environments and super-resolution mapping of dense microtubule arrays, and pave the way towards monitoring functional conformational changes of protein machines at high spatiotemporal resolution in living systems.

biophysics↗

bioRxiv2022

MicroFPGA: an affordable FPGA platform for microscope control

Modern microscopy relies increasingly on microscope automation to improve throughput, ensure reproducibility or observe rare events. Automation requires in particular computer control of the important elements of the microscope. Furthermore, optical elements that are usually fixed or manually movable can be placed on electronically-controllable elements. In most cases, a central electronics board is necessary to generate the control signals they require and to communicate with the computer. Fur such tasks, Arduino microcontrollers are widely used due to their low cost and programming entry barrier. However, they are limiting in their performance for applications that require high-speed or multiple parallel processes. Field programmable gate arrays (FPGA) are the perfect technology for high-speed microscope control, as they are capable of processing signals in parallel and with high temporal precision. While plummeting price made the technology available to consumers, a major hurdle remains the complex languages used to configure them. In this work, we used an affordable FPGA, delivered with an open-source and friendly-to-use programming language, to create a versatile microscope control platform called MicroFPGA. It is capable of synchronously triggering cameras and multiple lasers following complex patterns, as well as generating various signals used to control microscope elements such as filter wheels, servomotor stages, flip-mirrors, laser power or acoustooptic modulators. MicroFPGA is open-source and we provide online Micro-Manager, Java, Python and LabVIEW libraries, together with blueprints and tutorials.

biophysics↗

bioRxiv2022

Assessment of 3D MINFLUX data for quantitative structural biology in cells revisited

Prakash and Curd provide a re-analysis1 of individual datasets taken from our report2 demonstrating MINFLUX 3D imaging in cells. Their evaluation confirms the unique localization precision provided by MINFLUX2,3 featuring a standard deviation of {sigma} = 1-3 nm. We appreciate their confirmation and also welcome the opportunity to clarify their remaining points. The hitherto almost unconceivable 3D localization precision attained by MINFLUX is likely to hold the key to an all-optical dynamical structural biology.

biophysics↗

bioRxiv2021

Maximum-likelihood model fitting for quantitative analysis of SMLM data

Quantitative analysis is an important part of any single-molecule localization microscopy (SMLM) data analysis workflow to extract biological insights from the coordinates of the single fluorophores, but current approaches are restricted to simple geometries or do not work on heterogenous structures. Here, we present LocMoFit (Localization Model Fit), an open-source framework to fit an arbitrary model directly to the localization coordinates in SMLM data. Using maximum likelihood estimation, this tool extracts the most likely parameters for a given model that best describe the data, and can select the most likely model from alternative models. We demonstrate the versatility of LocMoFit by measuring precise dimensions of the nuclear pore complex and microtubules. We also use LocMoFit to assemble static and dynamic multi-color protein density maps from thousands of snapshots. In case an underlying geometry cannot be postulated, LocMoFit can perform single-particle averaging of super-resolution structures without any assumption about geometry or symmetry. We provide extensive simulation and visualization routines to validate the robustness of LocMoFit and tutorials based on example data to enable any user to increase the information content they can extract from their SMLM data.

biophysics↗

bioRxiv2021

Systematic Tuning of Rhodamine Spirocyclization for Super-Resolution Microscopy

Rhodamines are the most important class of fluorophores for applications in live-cell fluorescence microscopy. This is mainly because rhodamines exist in a dynamic equilibrium between a fluorescent zwitterion and a non-fluorescent but cell-permeable spirocyclic form. Different imaging applications require different positions of this dynamic equilibrium, which poses a challenge for the design of suitable probes. We describe here how the conversion of the ortho-carboxy moiety of a given rhodamine into substituted acyl benzenesulfonamides and alkylamides permits the systematic tuning of the equilibrium of spirocyclization with unprecedented accuracy and over a large range. This allows to transform the same rhodamine into either a highly fluorogenic and cell-permeable probe for live-cell stimulated emission depletion (STED) microscopy, or into a spontaneously blinking dye for single molecule localization microscopy (SMLM). We used this approach to generate differently colored probes optimized for different labeling systems and imaging applications.

cell biology↗

bioRxiv2020

3D super-resolution fluorescence microscopy maps the variable molecular architecture of the Nuclear Pore Complex

Nuclear pore complexes (NPCs) are large macromolecular machines that mediate the traffic between the nucleus and the cytoplasm. In vertebrates, each NPC consists of ~1000 proteins, termed nucleoporins, and has a mass of over 100 MDa. While a pseudo-atomic static model of the central scaffold of the NPC has recently been assembled by integrating data from isolated proteins and complexes, many structural components still remain elusive due to the enormous size and flexibility of the NPC. Here, we explored the power of 3D super-resolution microscopy combined with computational classification and averaging to explore the 3D structure of the NPC in single human cells. We show that this approach can build the first integrated 3D structural map containing both central as well as peripheral NPC subunits with molecular specificity and nanoscale resolution. Our unbiased classification of over ten thousand individual NPCs indicates that the nuclear ring and the nuclear basket can adopt different conformations. Our approach opens up the exciting possibility to relate different structural states of the NPC to function in situ.

cell biology↗

bioRxiv2019

MINFLUX nanoscopy delivers multicolor nanometer 3D-resolution in (living) cells

The ultimate goal of biological superresolution fluorescence microscopy is to provide three-dimensional resolution at the size scale of a fluorescent marker. Here, we show that, by localizing individual switchable fluorophores with a probing doughnut-shaped excitation beam, MINFLUX nanoscopy provides 1-3 nanometer resolution in fixed and living cells. This progress has been facilitated by approaching each fluorophore iteratively with the probing doughnut minimum, making the resolution essentially uniform and isotropic over scalable fields of view. MINFLUX imaging of nuclear pore complexes of a mammalian cell shows that this true nanometer scale resolution is obtained in three dimensions and in two color channels. Relying on fewer detected photons than popular camera-based localization, MINFLUX nanoscopy is poised to open a new chapter in the imaging of protein complexes and distributions in fixed and living cells.

biophysics↗

bioRxiv2019

Photoactivation of silicon rhodamines via a light-induced protonation

We present a new type of photoactivatable fluorophore that forms a bright silicon rhodamine derivative through a light-dependent isomerization followed by protonation. In contrast to other photoactivatable fluorophores, no caging groups are required, nor are there any undesired side-products released. Using this photoactivatable fluorophore, we created probes for HaloTag and actin for live-cell single-molecule localization microscopy and single-particle tracking experiments. The unusual mechanism of photoactivation and the fluorophores outstanding spectroscopic properties make it a powerful tool for live-cell super-resolution microscopy.

biophysics↗

bioRxiv2019

Nuclear pores as versatile reference standards for quantitative superresolution microscopy

Quantitative fluorescence and superresolution microscopy are often limited by insufficient data quality or artifacts. In this context, it is essential to have biologically relevant control samples to benchmark and optimize the quality of microscopes, labels and imaging conditions.\n\nHere we exploit the stereotypic arrangement of proteins in the nuclear pore complex as in situ reference structures to characterize the performance of a variety of microscopy modalities. We created four genome edited cell lines in which we endogenously labeled the nucleoporin Nup96 with mEGFP, SNAP-tag or HaloTag or the photoconvertible fluorescent protein mMaple. We demonstrate their use a) as 3D resolution standards for calibration and quality control, b) to quantify absolute labeling efficiencies and c) as precise reference standards for molecular counting.\n\nThese cell lines will enable the broad community to assess the quality of their microscopes and labels, and to perform quantitative, absolute measurements.

biophysics↗

bioRxiv2019

Depth-dependent PSF calibration and aberration correction for 3D single-molecule localization

3D Single molecule localization microscopy relies on fitting of the individual molecules with a point spread function (PSF) model. The reconstructed images often show local squeezing or expansion in z. A common cause are depth-induced aberrations in conjunction with an imperfect PSF model calibrated from beads on a coverslip, resulting in a mismatch between measured PSF and real PSF. Here, we developed a strategy for accurate z-localization in which we use the imperfect PSF model for fitting, determine the fitting errors and correct for them in a post-processing step. We present an open-source software tool and a simple experimental calibration procedure that allow retrieving accurate z-positions in any PSF engineering approach or fitting modality, even at large imaging depths.

biophysics↗

bioRxiv2017

Fast, robust and precise 3D localization for arbitrary point spread functions

We present a fitter for 3D single-molecule localization of arbitrary, experimental point spread functions (PSFs) that reaches minimum uncertainty for EMCCD and sCMOS cameras, and achieves more than 105 fits/s. We provide tools to robustly model experimental PSFs and correct for depth induced aberrations, which allowed us to achieve an unprecedented 3D resolution with engineered astigmatic PSFs, and acquire high quality 3D superresolution images even on standard microscopes without 3D optics.

biophysics↗