Biology subjects

Nettels, D.

Publications and source records attributed to Nettels, D..

6 recordsLinked to original sources

bioRxiv2026

Cooperativity, dynamics, and the free-energy surfaces of charge-patterned IDPs

The free-energy surfaces that underlie the conformational distributions of intrinsically disordered proteins (IDPs) are shallow and lack the deep minima characteristic of stable, folded structures. However, even in the absence of secondary or tertiary structure, sequence patterning can lead to conformational preferences and changes in chain dimensions as a function of solution conditions. While patterning effects have received extensive attention from simulation and theory, there is little corresponding data from experiment. Here we investigate the impact of charge patterning on chain dimensions and dynamics in a set of specifically designed polyampholytic IDP variants across the natural range of charge segregation with single-molecule FRET, nanosecond fluorescence correlation, circular dichroism, and NMR spectroscopy. We find that the conformational ensembles and their cooperative response to salt concentration show prominent and systematic dependencies on charge patterning, and to some extent on residue type. In contrast, the chain dynamics remain in the tens-of-nanosecond range, consistent with the absence of pronounced free-energy barriers. In close combination with molecular simulations, we show how the concept of susceptibility can be used to quantify cooperativity in the absence of barriers and relate it to the shallow free-energy surfaces of IDPs.

biophysics↗

bioRxiv2026

Phosphorylation tunes electrostatically driven protein-RNA interactions

Phosphorylation of intrinsically disordered proteins (IDPs) is essential for regulating biomolecular interactions in many cellular processes. However, a quantitative understanding of how phosphorylation tunes the affinity between highly charged IDPs and nucleic acids is lacking. Here, we show that multi-site phosphorylation of the disordered arginine/serine-rich (RS) domain of the splicing factor SRSF1 acts as an electrostatic rheostat that governs RNA binding. By combining enzymatic phosphorylation, phosphomimetic variants, and chemically synthesised phosphopeptides with single-molecule Forster resonance energy transfer measurements, we reveal the RS domain to be a potent driver of protein-RNA association. Increasing phosphorylation progressively reduces this interaction, and extensive phosphorylation eliminates detectable RNA binding. Remarkably, the binding free energy depends linearly on RS-domain net charge, regardless of whether the charge arises from phosphorylation or acidic residues introduced as phosphomimetics. Together, our findings uncover a quantitative framework for how phosphorylation tunes the interactions of charged IDPs and rationalize why two acidic residues are required to mimic a single phosphorylation event.

biophysics↗

bioRxiv2026

Time-Resolved Single-Molecule FRET Reveals Length-Dependent Nucleosome Decompaction by Poly(ADP-ribose)

Highly charged chains of poly(ADP-ribose) (PAR) are synthesized in the cell as part of their central role in DNA damage response. However, the effects of PAR on nucleosome structure and dynamics remain incompletely understood. Here we combine droplet-based microfluidic mixing with single-molecule Forster resonance energy transfer spectroscopy to resolve the kinetics of PAR-induced nucleosome decompaction in non-equilibrium measurements with millisecond time resolution. This approach avoids surface-adhesion and enables the tether-free observation of nucleosome remodeling. We find that PAR triggers nucleosome decompaction via a length-dependent kinetic threshold: Chains with less than ten ADP-ribose units act slowly and weakly, whereas longer PAR polymers induce efficient and rapid nucleosome opening. The extent and reversibility of decompaction further depend on PAR concentration and ionic strength, reflecting a mechanism dominated by electrostatic interactions. Enzymatic PAR digestion demonstrates that PAR can promote both reversible linker DNA opening and irreversible nucleosome disassembly. Coarse-grained molecular simulations suggest that these effects arise from a competition between PAR and DNA for histone tail binding. Altogether, our results establish PAR length as a key factor controlling chromatin accessibility during DNA repair and highlight droplet-based microfluidics as a powerful platform for studying such biomolecular interactions.

biophysics↗

bioRxiv2024

Model-free photon analysis of diffusion-based single-molecule FRET experiments

Photon-by-photon analysis tools for diffusion-based single-molecule Forster resonance energy transfer (smFRET) experiments often describe protein dynamics with Markov models. However, FRET efficiencies are only projections of the conformational space such that the measured dynamics can appear non-Markovian. Model-free methods to quantify FRET efficiency fluctuations would be desirable in this case. Here, we present such an approach. We determine FRET efficiency correlation functions free of artifacts from the finite length of photon trajectories or the diffusion of molecules through the confocal volume. We show that these functions capture the dynamics of proteins from micro-to milliseconds both in simulation and experiment, which provides a rigorous validation of current model-based analysis approaches.

biophysics↗

bioRxiv2022

Ultrafast molecular dynamics observed within a dense protein condensate

Many biological macromolecules can phase-separate in the cell and form highly concentrated condensates. The mesoscopic dynamics of these assemblies have been widely characterized, but their behavior at the molecular scale has remained more elusive. Here we investigate condensates of two highly charged disordered human proteins as a characteristic example of liquid-liquid phase separation. The dense phase is 1000 times more concentrated and has 300 times higher bulk viscosity than the dilute phase. However, single-molecule spectroscopy in individual droplets reveals that the polypeptide chains are remarkably dynamic, with sub-microsecond reconfiguration times. We rationalize this behavior with large-scale all-atom molecular-dynamics simulations, which reveal an unexpectedly similar short-range molecular environment in the dense and dilute phases, suggesting that local biochemical processes and interactions can remain exceedingly rapid in phase-separated systems.

biophysics↗

bioRxiv2020

Disordered Proteins Enable Histone Chaperoning on the Nucleosome

Proteins with highly charged disordered regions are abundant in the nucleus, where many of them interact with nucleic acids and control key processes such as transcription. The functional advantages conferred by protein disorder, however, have largely remained unclear. Here we show that disorder can facilitate a remarkable regulatory mechanism involving molecular competition. Single-molecule experiments demonstrate that the human linker histone H1 binds to the nucleosome with ultra-high affinity. However, the large-amplitude dynamics of the positively charged disordered regions of H1 persist on the nucleosome and facilitate the interaction with the highly negatively charged and disordered histone chaperone prothymosin . Consequently, prothymosin can efficiently invade the H1-nucleosome complex and displace H1 via competitive substitution. By integrating experiments and simulations, we establish a molecular model that rationalizes this process structurally and kinetically. Given the abundance of charged disordered regions in the nuclear proteome, this mechanism may be widespread in cellular regulation.

biophysics↗