Biology subjects

Schlierf, M.

Publications and source records attributed to Schlierf, M..

11 recordsLinked to original sources

bioRxiv2026

Complex folding kinetics of multi-domain proteins disentangled with periodic forces by magnetic tweezers

Force spectroscopy enables direct investigation of the interplay between free energy and transition kinetics in proteins and nucleic acids. However, multi-domain proteins often display multiple intermediate structures with diverse stabilities and kinetics, making equilibrium conditions difficult to achieve and out-of-equilibrium experiments challenging to interpret. We introduce a single-molecule force spectroscopy assay using periodic forces and high-resolution magnetic tweezers to bridge different stabilities, selectively enhance intermediate populations, and rigorously analyze multi-domain protein folding kinetics at quasi-equilibrium. By applying well-defined periodic square force functions with tunable steady states, we first validate our framework on the two-state folder {lambda}6-85, demonstrating that periodic force experiments can reproduce equilibrium kinetics. Extending this approach to the multi-domain protein mimic (Protein L), we show that tuning force, frequency, and amplitude enhances populations of distinct intermediate states. Finally, we dissect the entangled states of the hybrid two-domain protein {lambda}-L, where a 100-fold difference in domain kinetics precludes equilibrium analysis, by expanding from a two-state to a three-state periodic force protocol to direct intermediate populations. Our assay and analysis framework open new possibilities for deciphering complex multi-domain folds and their multi-dimensional folding pathways.

biophysics↗

bioRxiv2026

Nucleoid compaction during antibiotic stress excludes the SOS regulator LexA

The bacterial SOS response promotes DNA repair, survival, and mutagenesis under genotoxic stress, especially during sub-lethal antibiotic exposure. This response is regulated by LexA, a transcriptional repressor controlling SOS gene expression, but how LexA coordinates this network as antibiotic stress alters nucleoid structure is unclear. Using ciprofloxacin-induced DNA damage, we investigated how increasing antibiotic stress affects the spatial relationship between LexA and the nucleoid in single E. coli cells. Through 3D single-molecule imaging and functional assays, we found that sublethal ciprofloxacin doses activated SOS, expanded nucleoids, and maintained LexA association. In contrast, higher stress caused severe DNA damage, compacted nucleoids, and LexA exclusion, yet some cells remained viable and recovered after drug removal. These results demonstrate that the SOS response involves both temporal and spatial regulation, with LexA and nucleoid organization adapting to damage severity to modulate SOS functions.

microbiology↗

bioRxiv2026

Active destabilization of the integron synaptic complex reduces bacterial adaptation to antibiotics

Antibiotic multi-resistance (AMR) in bacteria poses a significant threat to global health, driven by mechanisms like the integron genetic system in Gram-negative bacteria. Integrons facilitate AMR by shuffling resistance genes through site-specific recombination, mediated by the integrase enzyme IntI. Earlier studies revealed that the mechanical stability of the synaptic complex, a structure formed by four integrase subunits and DNA, correlates with the recombination efficiency, and, by extension, the adaptation capability. We identified a conserved C-terminal -helix in IntI that stabilizes the synaptic complex via specific interactions with a binding pocket. To disrupt this interaction, we designed peptides mimicking the -helix, which reduced the mechanical stability probed with single-molecule optical tweezers. In bacterial adaptation assays, these peptides significantly decreased integron-mediated adaptation to ciprofloxacin stress without exhibiting antimicrobial activity. This approach highlights a novel strategy to combat AMR by targeting integron-mediated gene shuffling, offering potential for future therapeutic development to limit the spread of resistance genes.

biophysics↗

bioRxiv2025

Spatiotemporal Dynamics of the Dihydrolipoyl Dehydrogenase LpdA Determine the Intrinsic Autofluorescence in Filamentous Actinobacteria

The hyphal nature of filamentous streptomycetes poses unique challenges to their multicellular lifestyle, since it requires organizing cellular functions at the scale of hundreds of micrometers length. Streptomycetes exhibit a strong and patchy autofluorescence of so far unknown origin in their hyphae that - as we demonstrate - is a natural property of filamentous actinobacteria. The foci are dynamic and evenly distributed throughout the hyphae, including the hyphal tips, where they are cell membrane-associated. Here, we resolved the high spatiotemporal dynamics of these foci during spore germination and vegetative growth in Streptomyces venezuelae. We isolated a fluorescent protein band and identified the responsible protein as dihydrolipoyl dehydrogenase LpdA. An lpdA deletion mutant lacked these fluorescent foci and showed minor deficiencies in growth and development. Heterologous LpdA production in E. coli and characterization of the enzyme verified that a flavin cofactor is responsible for the green autofluorescence. LpdA is highly conserved in actinomycetes as a part of multienzyme complexes involved in central metabolism. Such delocalized metabolic centers provide a potential solution to mycelial multicellular lifestyle, where diffusion becomes a major challenge.

microbiology↗

bioRxiv2024

The recombination efficiency of the bacterial integron depends on the mechanical stability of the synaptic complex

The predominant tool for adaptation in Gram-negative bacteria is a genetic system called integron. Under conditions of stress, it rearranges gene cassettes, ensuring their sampling through expression, to offer a solution for overcoming the initial stress. Integrons are a major actor of multiple antibiotic resistances, a recognized major global health threat. Cassettes are recombined by a unique recombination process involving a tyrosine recombinase - the IntI integrase - and folded single-stranded DNA hairpins - the attC sites which terminate each cassette. Four recombinases and two attC sites form a macromolecular synaptic complex, which is key to the recombination process and the focus of our study. The bottom strand of all attC sites shows highest recombination efficiency in vivo than the top one, however, the efficiency still varies several orders of magnitude and the underlying reason remains unclear. Here, we established an optical tweezers force-spectroscopy assay that allows us to probe the synaptic complex stability. We found for seven combinations of attC sites great variability in the mechanical stability. Two protein variants also showed a strong influence on the mechanical stability. We then determined the in vivo recombination efficiencies of the different attC site combinations and protein variants and discovered a strong correlation between recombination efficiency and mechanical stability of the synaptic complex, indicating a regulatory mechanism from the DNA sequence to the macromolecular complex stability. Taking into account known forces during DNA metabolism, we suggest that the variation of the in vivo recombination efficiency is mediated strongly by the synaptic complex stability.

biophysics↗

bioRxiv2023

Farewell to single-well: An automated single-molecule FRET platform for high-content, multiwell plate screening of biomolecular conformations and dynamics

Single-molecule FRET (smFRET) has become a widely used tool for probing the structure, dynamics, and functional mechanisms of biomolecular systems, and is extensively used to address questions ranging from biomolecular folding to drug discovery. Investigations by smFRET often require sampling of a large parameter space, for example, by varying one or more constituent molecular components in ten or more steps to reliably extract distances, kinetic rates, and other quantitative parameters. Confocal smFRET measurements, for example, which are amongst the widely used smFRET assays, are typically performed in a single-well format and measurements are conducted in a manual manner, making sampling of many experimental parameters laborious and time consuming. To address this challenge, we extend here the capabilities of confocal smFRET beyond single-well measurements by integrating a multiwell plate functionality into a confocal microscope to allow for continuous and automated smFRET measurements. We show that the multiwell plate assay is on par with conventional single-well smFRET measurements in terms of accuracy and precision yet enables probing tens to hundreds of conditions in a fully automized manner. We demonstrate the broad applicability of the multiwell plate assay towards DNA hairpin dynamics, protein folding, and competitive and cooperative protein-DNA interactions, revealing new insights that would be hard if not impossible to achieve with conventional single-well format measurements. The higher sampling density afforded by the multiwell plate format increases the accuracy of data analysis by at least 10-fold. We further showcase that the assay provides access to smFRET-based screening of drug-protein interactions. For the adaptation into existing instrumentations, we provide a detailed guide and open-source acquisition and analysis software. Taken together, the automated multiwell plate assay developed here opens up new possibilities to acquire high-content smFRET datasets for in-depth single-molecule analysis of biomolecular conformations, interactions, and dynamics.

biophysics↗

bioRxiv2022

Reliability and accuracy of single-molecule FRET studies for characterization of structural dynamics and distances in proteins

Single-molecule FRET (smFRET) has become an established tool to study biomolecular structure and dynamics in vitro and in live cells. We performed a worldwide blind study involving 19 labs to assess the uncertainty of FRET experiments for proteins with respect to the measured FRET efficiency histograms, determination of distances, and the detection and quantification of structural dynamics. Using two protein systems that undergo distinct conformational changes, we obtained an uncertainty of the FRET efficiency of less than {+/-} 0.06, corresponding to an interdye distance precision of [≤] 0.2 nm and accuracy of [≤] 0.5 nm. We further discuss the limits for detecting distance fluctuations with sensitivity down to [lsim] 10% of the Forster distance and provide guidelines on how to detect potential dye perturbations. The ability of smFRET experiments to simultaneously measure distances and avoid averaging of conformational dynamics slower than the fluorescence lifetime is unique for dynamic structural biology.

biophysics↗

bioRxiv2021

Chaperones Skp and SurA dynamically expand unfolded outer membrane protein X and synergistically disassemble oligomeric aggregates

Periplasmic chaperones Skp and SurA are essential players in outer membrane protein (OMP) biogenesis. They prevent unfolded OMPs from misfolding during their passage through the periplasmic space and aid in the disassembly of OMP aggregates under cellular stress conditions. However, functionally important links between interaction mechanisms, structural dynamics, and energetics that underpin both Skp and SurA association with OMPs have remained largely unresolved. Here, using single-molecule fluorescence spectroscopy, we dissect the conformational dynamics and thermodynamics of Skp and SurA binding to unfolded OmpX, and explore their disaggregase activities. We show that both chaperones expand unfolded OmpX distinctly and induce microsecond chain reconfigurations in the client OMP structure. We further reveal that Skp and SurA bind their substrate in a fine-tuned thermodynamic process via enthalpy-entropy compensation. Finally, we observed synergistic activity of both chaperones in the disaggregation of oligomeric OmpX aggregates. Our findings provide an intimate view into the multi-faceted functionalities of Skp and SurA and the fine-tuned balance between conformational flexibility and underlying energetics in aiding chaperone action during OMP biogenesis.

biophysics↗

bioRxiv2020

Direct visualization of four diffusive LexA states controlling SOS response strength during antibiotic treatment

In bacteria, the key mechanism governing mutation, adaptation and survival upon DNA damage is the SOS response. Through autoproteolytic digestion triggered by single-stranded DNA caused by most antibiotics, the transcriptional repressor LexA controls over 50 SOS genes including DNA repair pathways and drivers of mutagenesis. Efforts to inhibit this response and thereby combat antibiotic resistance rely on a broad understanding of its behavior in vivo, which is still limited. Here, we develop a single-molecule localization microscopy assay to directly visualize LexA mobility in Escherichia coli and monitor the SOS response on the level of transcription factor activity. We identify four diffusive populations and monitor their temporal evolution upon ciprofloxacin-induced continuous DNA damage. With LexA mutants, we assign target bound, non-specifically DNA bound, freely diffusing and cleaved repressors. We develop a strategy to count LexA in fixed cells at different time points after antibiotic stress and combine the time-evolution of LexA sub-populations and the repressors overall abundance. Through fitting a detailed kinetic model we obtain in vivo synthesis, cleavage and binding rates and determined that the regulatory feedback system reaches a new equilibrium in [~]100 min. LexA concentrations showed non-constant heterogeneity during SOS response and designate LexA expression, and thereby regulation of downstream SOS proteins, as drivers of evolutionary adaptation. Even under low antibiotic stress, we observed a strong SOS response on the LexA level, suggestion that small amounts of antibiotics can trigger adaptation in E. coli.

biophysics↗

bioRxiv2018

Hexameric helicase G40P unwinds DNA in single base pair steps

Most replicative helicases are hexameric, ring-shaped motor proteins that translocate on and unwind DNA. Despite extensive biochemical and structural investigations, how their translocation activity is utilized chemo-mechanically in DNA unwinding is poorly understood. We examined DNA unwinding by G40P, a DnaB-family helicase, using a single-molecule fluorescence assay with a single base pair resolution. The high-resolution assay revealed that G40P by itself is a very weak helicase that stalls at barriers as small as a single GC base pair and unwinds DNA with the step size of a single base pair. Single ATP{gamma}S binding could stall unwinding, demonstrating highly coordinated ATP hydrolysis between the six identical subunits. We observed frequent slippage of the helicase, which is fully suppressed by the primase DnaG. We anticipate that these findings allow a better understanding on the fine balance of thermal fluctuation activation and energy derived from hydrolysis.

biophysics↗

bioRxiv2018

ATPase and protease domain movements in the bacterial AAA+ protease FtsH are driven by thermal fluctuations

AAA+ proteases are essential players in cellular pathways of protein degradation. Elucidating their conformational behavior is key for understanding their reaction mechanism and, importantly, for elaborating our understanding of mutation-induced protease deficiencies. Here, we study the structural dynamics of the Thermotoga maritima AAA+ hexameric ring metalloprotease FtsH (TmFtsH). Using a single-molecule Forster resonance energy transfer approach to monitor ATPase and protease inter-domain conformational changes in real time, we show that TmFtsH--even in the absence of nucleotide--is a highly dynamic protease undergoing conformational transitions between five states on the second timescale in a sequential manner. Addition of ATP does not influence the number of states nor change the timescale of domain motions, but affects the state occupancy distribution leading to an inter-domain compaction. These findings suggest that thermal energy, but not chemical energy, provides the major driving force for conformational switching, while ATP, through a state reequilibration, introduces directionality into this process. The TmFtsH A359V mutation, a homolog of the human pathogenic A510V mutation of paraplegin (SPG7) causing hereditary spastic paraplegia (HSP), does not affect the dynamic behavior of the protease but impairs the ATP-coupled domain compaction and, thus, may account for protease malfunctioning and pathogenesis in HSP.

molecular biology↗