Biology subjects

Adam, V.

Publications and source records attributed to Adam, V..

6 recordsLinked to original sources

bioRxiv2024

Decoding mEos4b Day-Long Maturation and Engineering Fast Maturing Variants

The maturation speed of fluorescent proteins is a crucial parameter that influences cellular brightness, effective labeling efficiency and temporal resolution in fluorescence microscopy. Green-to-red photoconvertible fluorescent proteins (PCFPs) used in pulse-chase experiments and super-resolution techniques such as Photoactivated Localization Microscopy (PALM), single-particle-tracking PALM (sptPALM) and Minimal Fluorescence Photon Fluxes Microscopy (MINFLUX) may be hampered by slow maturation. We systematically characterized the maturation speed of mEos-derived PCFPs in E. coli and found that, in contrast to pcStar and mEosEM, several variants such as mEos2, mEos3.1, mEos3.2 and mEos4b mature extremely slowly. Strikingly, the oxidation step in those PCFPs is fast and not rate-limiting. Through a rational mutagenesis approach, we developed a strategy to reduce the day-long maturation time of mEos4b by nearly two orders of magnitude without significantly impacting its molecular brightness and photophysical performance under single-molecule imaging conditions.

biophysics↗

bioRxiv2022

Photophysical studies at cryogenic temperature reveal a novel photoswitching mechanism of rsEGFP2

Single-molecule-localization-microscopy (SMLM) at cryogenic temperature opens new avenues to investigate intact biological samples at the nanoscale and perform cryo-correlative studies. Genetically encoded fluorescent proteins (FPs) are markers of choice for cryo-SMLM, but their reduced conformational flexibility below the glass transition temperature hampers efficient photoswitching at low temperature. We investigated cryo-switching of rsEGFP2, one of the most efficient reversibly switchable fluorescent protein at ambient temperature due to facile cis-trans isomerization of the chromophore. UV-visible microspectrophotometry and X-ray crystallography revealed a completely different switching mechanism at [~]110 K. At this cryogenic temperature, on-off photoswitching involves the formation of 2 dark states with blue shifted absorption relative to that of the trans protonated chromophore populated at ambient temperature. Only one of these dark states can be switched back to the fluorescent state by 405 nm light, while both of them are sensitive to UV light at 355 nm. The rsEGFP2 photoswitching mechanism discovered in this work adds to the panoply of known switching mechanisms in fluorescent proteins. It suggests that employing 355 nm light in cryo-SMLM experiments using rsEGFP2 or possibly other FPs could improve the achievable effective labeling efficiency in this technique. Table of Contents artwork O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/504779v1_ufig1.gif" ALT="Figure 1"> View larger version (76K): org.highwire.dtl.DTLVardef@1d5ed02org.highwire.dtl.DTLVardef@1bb2359org.highwire.dtl.DTLVardef@10dc6b1org.highwire.dtl.DTLVardef@16fcd94_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2021

Rational control of structural off-state heterogeneity in a photoswitchable fluorescent protein provides switching contrast enhancement

Reversibly photoswitchable fluorescent proteins are essential markers for advanced biological imaging, and optimization of their photophysical properties underlies improved performance and novel applications. Here we establish a link between photoswitching contrast, a key parameter that largely dictates the achievable resolution in nanoscopy applications, and chromophore conformation in the non-fluorescent state of rsEGFP2, a widely employed label in REversible Saturable OpticaL Fluorescence Transitions (RESOLFT) microscopy. Upon illumination, the cis chromophore of rsEGFP2 isomerizes to two distinct off-state conformations, trans1 and trans2, located on either side of the V151 side chain. Reducing or enlarging the side chain at this position (V151A and V151L variants) leads to single off-state conformations that exhibit higher and lower switching contrast, respectively, compared to the rsEGFP2 parent. The combination of structural information obtained by serial femtosecond crystallography with high-level quantum chemical calculations and with spectroscopic and photophysical data determined in vitro suggests that the changes in switching contrast arise from blue- and red-shifts of the absorption bands associated to trans1 and trans2, respectively. Thus, due to elimination of trans2, the V151A variants of rsEGFP2 and its superfolding variant rsFolder2 display a more than two-fold higher switching contrast than their respective parent proteins, both in vitro and in E. coli cells. The application of the rsFolder2-V151A variant is demonstrated in RESOLFT nanoscopy. Our study rationalizes the connection between structural and photophysical chromophore properties and suggests a means to rationally improve fluorescent proteins for nanoscopy applications.

biophysics↗

bioRxiv2020

Supramolecular assembly of the E. coli LdcI upon acid stress

Pathogenic and commensal bacteria often have to resist the harsh acidity of the host stomach. The inducible lysine decarboxylase LdcI buffers the cytosol and the local extracellular environment to ensure enterobacterial survival at low pH. Here, we investigate the acid-stress response regulation of E. coli LdcI by combining biochemical and biophysical characterisation with negative stain and cryo-electron microscopy, and wide-field and super-resolution fluorescence imaging. Due to deleterious effects of fluorescent protein fusions on native LdcI decamers, we opt for three-dimensional localisation of nanobody-labelled endogenous wild-type LdcI in acid-stressed E. coli cells, and show that it organises into distinct patches at the cell periphery. Consistent with recent hypotheses that in vivo clustering of metabolic enzymes often reflects their polymerisation as a means of stimulus-induced regulation, we show that LdcI assembles into filaments in vitro at physiologically relevant low pH. We solve the structures of these filaments and of the LdcI decamer formed at neutral pH by cryo-electron microscopy, and reveal the molecular determinants of LdcI polymerisation, confirmed by mutational analysis. Finally, we propose a model for LdcI function inside the enterobacterial cell, providing a structural and mechanistic basis for further investigation of the role of its supramolecular organisation in the acid stress response.Significance statement Bacteria possess a sophisticated arsenal of defence mechanisms that allow them to survive in adverse conditions. Adaptation to acid stress and hypoxia is crucial for the enterobacterial transmission in the gastrointestinal tract of their human host. When subjected to low pH, E. coli and many other enterobacteria activate a proton-consuming resistance system based on the acid-stress inducible lysine decarboxylase LdcI. Here we develop generally-applicable tools to uncover the spatial localisation of LdcI inside the cell by super-resolution fluorescence microscopy, and investigate the in vitro supramolecular organisation of this enzyme by cryo-EM. We build on these results to propose a mechanistic model for LdcI function and offer tools for further in vivo investigations.Competing Interest StatementThe authors have declared no competing interest.View Full Text

microbiology↗

bioRxiv2019

NMR reveals light-induced changes in the dynamics of a photoswitchable fluorescent protein

The availability of fluorescent proteins with distinct phototransformation properties is crucial for a wide range of applications in advanced fluorescence microscopy and biotechnology. To rationally design new variants optimized for specific applications, a detailed understanding of the mechanistic features underlying phototransformation is essential. At present, little is known about the conformational dynamics of fluorescent proteins at physiological temperature, and how these dynamics contribute to the observed phototransformation properties. Here, we apply high-resolution NMR spectroscopy in solution combined with in-situ sample illumination at different wavelengths to investigate the conformational dynamics of rsFolder, a GFP-derived protein that can be reversibly switched between a green fluorescent state and a non-fluorescent state. Our results add a dynamic view to the static structures obtained by X-ray crystallography. Including NMR into the analytical toolbox used for fluorescent protein research provides new opportunities for investigating the effect of mutations or changes in the environmental conditions on the conformational dynamics of phototransformable fluorescent proteins, and their correlation with the observed photochemical and photophysical properties.\n\nSignificancePhoto-transformable Fluorescent Proteins (PTFPs) are essential tools for super-resolution (SR) microscopy. In practical applications, however, researchers often encounter problems when using PTFPs in a particular cellular context, because the environmental conditions (pH, temperature, redox potential, oxygen level, viscosity, ...) affect their brightness, photostability, phototransformation kinetics, etc. Rational fluorescent protein engineering exploits the mechanistic information available from structural studies, mainly X-ray crystallography, in order to design new PTFP variants with improved properties for particular applications. Here we apply NMR spectroscopy in solution to investigate the light-induced changes in conformational dynamics of rsFolder, a reversibly switchable fluorescent protein. The dynamic view offered by NMR highlights protein regions that comprise potentially interesting mutation points for future mutagenesis campaigns.

biophysics↗

bioRxiv2018

Mechanistic investigation of mEos4b reveals a strategy to reduce track interruptions in sptPALM

Green-to-red photoconvertible fluorescent proteins repeatedly enter dark states, causing interrupted tracks in single-particle-tracking localization microscopy (sptPALM). We identified a long-lived dark state in photoconverted mEos4b that results from isomerization of the chromophore and efficiently absorbs cyan light. Addition of weak 488-nm light swiftly reverts this dark state to the fluorescent state. This strategy largely eliminates slow blinking and enables the recording of significantly longer tracks in sptPALM with minimum effort.

biophysics↗