Biology subjects

Hugel, T.

Publications and source records attributed to Hugel, T..

13 recordsLinked to original sources

bioRxiv2026

More insights into the dynamic assembly and rotation of the archaellum motor machinery

Archaea use the archaellum for swimming motility. Rotation of the archaellum is driven by the ATPase ArlI and the membrane platform protein ArlJ. Structural studies suggest that conformational changes in ArlI power the rotation of ArlJ. However, how ATP hydrolysis is converted into rotation remains poorly under-stood. Using single-molecule total internal reflection fluorescence (TIRF) microscopy, we show that dimeric ArlJ forms a complex with ArlI. Combining conservation analysis, AlphaFold3 predictions and co-purifications, we identified conserved ArlJ residues required for interaction with ArlI, including a structural-ly rigid loop and the critical residue R341 at the ArlI interface. Motility assays in Haloferax volcanii confirmed these findings. Together, these findings support a model in which a dimeric ArlJ is interacting with ArlI via conserved residues to generate torque.

microbiology↗

bioRxiv2024

TAF2 condensation in nuclear speckles links basal transcription factor TFIID to RNA splicing

TFIID is an essential basal transcription factor, crucial for RNA polymerase II (pol II) promoter recognition and transcription initiation. The TFIID complex consists of the TATA-binding protein (TBP) and 13 TBP-associated factors (TAFs) that contain intrinsically disordered regions (IDRs) with currently unknown functions. Here, we show that a conserved IDR drives TAF2 condensation in nuclear speckles, independently of other TFIID subunits. Quantitative mass spectrometry analyses reveal that the TAF2 IDR specifically interacts with the nuclear speckle and spliceosome-associated protein SRRM2. Consequently, TAF2 recruits SRRM2 to TFIID to form non-canonical TFIID-SRRM2 complexes. Reduced SRRM2 recruitment elicits alternative splicing events in RNAs coding for proteins involved in transcription and transmembrane transport. Further, genome-wide binding analyses suggest TAF2 shuttling between nuclear speckles and pol II promoters. This study identifies an IDR of the basal transcription machinery as a molecular guide for protein partitioning into nuclear compartments, controlling protein complex composition and pre-mRNA splicing.

molecular biology↗

bioRxiv2023

Single-molecule FRET and tracking of transfected biomolecules: multi-dimensional protein dynamics in living cells

Proteins and DNA in cells exhibit different conformational states, which are influenced by dynamic interactions with other biomolecules. All these interactions are affected by the molecules localization within the cell, i.e., their compartmentalization. Such, in cellula, compartment-specific dynamics is difficult to measure, because of limitations in instrumentation, autofluorescence of cells, and the necessity to track diffusing molecules. Here, we present a bottom-up engineering approach, which allows us to track transfected proteins in cellula and to analyze time-resolved single-molecule FRET efficiencies. This has been achieved by alternating laser excitation (ALEX) based three-channel (donor, acceptor and FRET) tracking with a live-cell HILO microscope. We validate our strategy by characterizing long-term static-FRET traces of customized DNA with known dye positions. We utilize two different transfection strategies, namely a biological (Streptolysin-O toxin protein) and a physical one (Microinjection). By comparing in vitro and in cellula measurements we show that the cellular environment in this case changes the FRET efficiency by about 25%. In addition, we evaluate single-molecule FRET traces for the heat shock protein Hsp90 in cellula. The obtained FRET efficiency distribution is largely consistent with known Hsp90 structures and in vitro distributions, but also shows some clear differences. Altogether, we show that FRET-TTB (Forster Resonance Energy Transfer-Tracking of Transfected Biomolecules) opens the path to study protein state changes of transfected biomolecules in cellula, including time-resolved cellular localization. SignificanceInside cells, proteins and DNA can change shape depending on their environment and their interactions. Studying these changes for single biomolecules is challenging because they move around in the cell and the cell environment makes it hard to see them clearly. Here, we demonstrate a new technique called FRET-TTB that enables us to track individual proteins inside living cells over time using single-molecule fluorescence microscopy. We validate the approach with custom DNA and apply it to study the heat shock protein Hsp90. Our results show that this method can reveal changes in protein conformation and location within living cells.

biophysics↗

bioRxiv2023

Cochaperones convey the energy of ATP hydrolysis for directional action of Hsp90

The molecular chaperone and heat shock protein Hsp90 is part of many protein complexes in eukaryotic cells. Together with its cochaperones, Hsp90 is responsible for the maturation of hundreds of clients. Although having been investigated for decades, it still is largely unknown which components are necessary for a functional complex and how the energy of ATP hydrolysis is used to enable cyclic operation. Here we use single-molecule FRET to show how cochaperones introduce directionality into Hsp90s conformational changes during its interaction with the client kinase Ste11. Most interestingly, three cochaperones are needed to couple ATP turnover to these conformational changes. All three are therefore essential for a functional cyclic operation, which requires coupling to an energy source. Finally, our findings show how the formation of sub-complexes in equilibrium followed by a directed selection of the functional complex can be the most energy efficient pathway for kinase maturation.

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↗

bioRxiv2022

Quantitative real-time in-cell imaging reveals heterogeneous clusters of proteins prior to condensation

The formation of biomolecular condensates underpins many cellular processes; however, our current understanding of condensate formation within cells is largely based on observing the final near-equilibrium condensate state. It is less clear how proteins behave before condensates form or at concentrations at which condensation does not occur in cells. Here, we use a combination of fluorescence microscopy and photobleaching analysis to quantify phase separation of negative elongation factor (NELF) in living and stressed cells. We use the recently reported system of stress-induced condensation of NELF in human nuclei as a model to study the behaviour of proteins before condensation. We find that pre-condensate heterogeneous clusters both grow and shrink and are not freely diffusing. Unexpectedly, we also find such small dynamic clusters in unstressed cells in which condensates do not form. We provide a categorisation of small and large clusters based on their dynamics and their response to p38 kinase inhibition. Overall, our data are best explained as non-classical nucleation with a flat free-energy landscape for clusters of a range of sizes and an inhibition of condensation.

biophysics↗

bioRxiv2021

Inferring kinetic rate constants from single-molecule FRET trajectories - a blind benchmark of kinetic analysis tools

Single-molecule FRET (smFRET) is a versatile technique to study the dynamics and function of biomolecules since it makes nanoscale movements detectable as fluorescence signals. The powerful ability to infer quantitative kinetic information from smFRET data is, however, complicated by experimental limitations. Diverse analysis tools have been developed to overcome these hurdles but a systematic comparison is lacking. Here, we report the results of a blind benchmark study assessing eleven analysis tools used to infer kinetic rate constants from smFRET trajectories. We tested them against simulated and experimental data containing the most prominent difficulties encountered in analyzing smFRET experiments: different noise levels, varied model complexity, non-equilibrium dynamics, and kinetic heterogeneity. Our results highlight the current strengths and limitations in inferring kinetic information from smFRET trajectories. In addition, we formulate concrete recommendations and identify key targets for future developments, aimed to advance our understanding of biomolecular dynamics through quantitative experiment-derived models.

biophysics↗

bioRxiv2021

Autophosphorylation of the KaiC-like protein ArlH inhibits oligomerisation and interaction with ArlI, the motor ATPase of the archaellum

Motile archaea are propelled by the archaellum, whose motor complex consists of the membrane protein ArlJ, the ATPase ArlI, and the ATP-binding protein ArlH. Despite its essential function and the existence of structural and biochemical data on ArlH, the role of ArlH in archaellum assembly and function remains elusive. ArlH is a structural homolog of KaiC, the central component of the cyanobacterial circadian clock. Similar to KaiC, ArlH exhibits autophosphorylation activity, which was observed for both ArlH of the euryarchaeon Pyrococcus furiosus (PfArlH) and the crenarchaeon Sulfolobus acidocaldarius (SaArlH). Using a combination of single molecule fluorescence measurements and biochemical assays, it is shown that autophosphorylation of ArlH is closely linked to the oligomeric state of ArlH bound to ArlI. These experiments also strongly suggest that ArlH is a hexamer in its functional ArlI bound state. Mutagenesis of the putative catalytic residue Glu-57 in SaArlH results in a reduced autophosphorylation activity and abolished archaellation and motility, suggesting that optimum phosphorylation activity of ArlH is essential for both archaellation and motility.

microbiology↗

bioRxiv2020

Allosteric action of nucleotides on Hsp90 across several time- and length scales

I. ABSTRACTSeveral indicators for a signal propagation from a binding site to a distant functional site have been found in the Hsp90 dimer. Here we determined a time-resolved pathway from ATP hydrolysis to changes in a distant folding substrate binding site. This was possible by combining single-molecule fluorescence-based methods with extensive atomistic nonequilibrium molecular dynamics simulations. We find that hydrolysis of one ATP effects a structural asymmetry in the full Hsp90 dimer that leads to the collapse of a central folding substrate binding site. Arg380 is the major mediator in transferring structural information from the nucleotide to the substrate binding site. This allosteric process occurs via hierarchical dynamics that involve timescales from picoto milliseconds and length scales from Ångstroms to several nanometers. We presume that similar hierarchical mechanisms are fundamental for information transfer through many other proteins.Competing Interest StatementThe authors have declared no competing interest.View Full Text

biophysics↗

bioRxiv2019

Same Equilibrium. Different Kinetics. Protein Functional Consequences.

In a living cell, protein function is regulated in several ways, including post-translational modifications (PTMs), protein-protein interaction, or by the global environment (e.g. crowding or phase separation). While site-specific PTMs act very locally on the protein, specific protein interactions typically affect larger (sub-)domains, and global changes affect the whole protein in non-specific ways. Herein, we directly observe protein regulation in three different degrees of localization, and present the effects on the Hsp90 chaperone system at the levels of conformational equilibria, kinetics and protein function. Interestingly using single-molecule FRET, we find that similar functional and conformational steady-states are caused by completely different underlying kinetics. Solving the complete kinetic rate model allows us to disentangle specific and non-specific effects controlling Hsp90s ATPase function, which has remained a puzzle up to this day. Lastly, we introduce a new mechanistic concept: functional stimulation through conformational confinement. Our results highlight how cellular protein regulation works by fine-tuning the conformational state space of proteins. SignificanceProteins are perceived more and more as dynamic systems whose function depends critically on local and global flexibility. While 3D structures of proteins are frequently available today, our models often lack the time component, namely rate constants that determine protein function and regulation. Here we used single-molecule FRET to elucidate how the chaperone protein Hsp90 is regulated on various levels, locally and globally. We find that ATPase stimulation occurs not only through specific interactions, but also non-specifically by reducing non-productive conformational flexibility; i.e. by changing kinetics rather than thermodynamics. Our work introduces stimulation through conformational confinement as a general mechanistic concept. We anticipate that this concept plays an important role in protein regulation, phase separation, and in dynamic protein systems in general.

biophysics↗

bioRxiv2019

Proof-of-concept for the detection of early osteoarthritis pathology by endomicroscopy

Osteoarthritis (OA) is a degenerative joint disease and the leading cause of global disability. Clinical trials to date have been unable to pinpoint early and potentially reversible disease states with current clinical technology and hence disease-modifying OA drug candidates cannot be tested early in the disease. To overcome this obstacle, we correlate articular cartilage stiffness changes and cellular spatial organization. The former is a well-understood and functionally relevant OA pathology, while the latter allows discriminating between healthy vs early OA, based on distinct cellular spatial patterns. We demonstrated that an extensive loss of atomic force microscopy-detected stiffness can be seen in cartilage tissues with spatial patterns exhibiting the earliest identifiable OA. In addition, the translation of commercially available clinically usable probe-based confocal laser-endomicroscopy allows us to detect these early OA spatial patterns. This study resolves a major clinical trial obstacle by presenting the proof-of-concept that early OA pathology can be detected by already available clinical technology.\n\nOne Sentence SummaryWe report a correlation between articular cartilage surface nanoscale stiffness and chondrocyte spatial organization; using this correlation enables early pathology detection by currently available clinical optical methods.

biophysics↗

bioRxiv2018

Effects of inhibitors on Hsp90’s conformational dynamics, cochaperone and client interactions

The molecular chaperone and heat-shock protein Hsp90 has become a central target in anti-cancer therapy. Nevertheless, the effect of Hsp90 inhibition is still not understood at the molecular level, preventing a truly rational drug design. Here we report on the effect of the most prominent drug candidates, namely radicicol, geldanamycin, derivatives of purine and novobiocin, on Hsp90s characteristic conformational dynamics and the binding of three interaction partners. Unexpectedly, the global opening and closing transitions are hardly affected by Hsp90 inhibitors. Instead, the conformational equilibrium, as well as the associated kinetic rate constants remain almost untouched. Moreover, we find no significant changes in the binding of the cochaperones Aha1 and p23 nor of the model substrate {Delta}131{Delta}. This holds true for both, competitive and allosteric inhibitors. Therefore, direct inhibition mechanisms, affecting only one molecular interaction, are unlikely. Based on our results, we speculate that the inhibitory action observed in vivo is caused by a combination of subtle effects, which can be used in the search for novel Hsp90 inhibition mechanisms.

biochemistry↗

bioRxiv2017

Cooperative nucleotide binding in Hsp90 and the underlying mechanisms

The function of the molecular chaperone Hsp90 depends on large conformational changes, rearrangement of local motifs, as well as the binding and hydrolysis of ATP. The complexity of the Hsp90 system impedes the detailed investigation of their interplay using standard methods. By the application of three-color single molecule FRET to Hsp90 and a reporter nucleotide, we directly observe cooperativity between the two nucleotide binding pockets in the protein dimer. Through allocating the microscopic states and extracting their kinetics, we identify the mechanisms underlying the cooperativity. Surprisingly, nucleotide binding affects several state transitions, which demonstrates the complexity of cooperativity in protein systems. The co-chaperone Aha1, known to accelerate Hsp90's ATPase activity, adds another layer of complexity by affecting transitions in a nucleotide-dependent and -independent manner.

biophysics↗