Biology subjects

Sosnick, T.

Publications and source records attributed to Sosnick, T..

7 recordsLinked to original sources

bioRxiv2026

CRANBERRY: An RNA Dynamics Model with Sugar Puckering and Noncanonical Base Pairing

We introduce a new coarse-grained model ''CRANBERRY'' that incorporates sugar puckering and non-canonical base pairing, two factors central to RNA structure and dynamics, yet rarely included in most coarse-grained models. Our model is parameterized through a contrastive divergence approach, combined with fine-tuning strategies to improve accuracy in generating disordered states, a feature that is critical for the accurate description of thermodynamics. This two-stage training procedure greatly enhances cooperative folding behavior. Due to these advances, the model's predictive performance is comparable to that of all-atom force fields for native-state structural fluctuations. Furthermore, CRANBERRY exhibits better agreement with experimental data on stacking free energies and disordered structures measured by Small Angle X-ray Scattering. In addition, CRANBERRY can reversibly fold tetraloops with a minimum RMSD of 1.4 Angstrom de novo, which continues to be challenging for all-atom models. It predicts melting temperatures in agreement with experimental values, and with a greater cooperativity than all-atom predictions.

biophysics↗

bioRxiv2025

Structural Mechanism of Prestin-Membrane Mechanotransduction

Sound frequency discrimination in mammals depends on the conformational transitions of prestin (SLC26A5), the piezoelectric motor in outer hair cells. The mechanism that enables prestins electrically driven interconversion and its dependence on membrane mechanics, remains unresolved. Here, we show that membrane forces represent a strong driver of the same conformational changes generated by transmembrane voltage and stabilized by bound anions. Single particle cryo-EM structures of nanodisc-reconstituted prestin were obtained from varying lipid composition and membrane thickness. These structures show that membrane thinning biases prestin from a compact conformation to a fully expanded conformation, mimicking outer hair cell elongation/contraction during electromotility. In contrast, zebrafish SLC26A5 transporters undergo complete elevator movements with redistribution of areal changes across leaflets. The structures, together with mutagenesis, H/D exchange mass spectrometry data, and NLC measurements, offer a high-resolution understanding of how prestin translates membrane tension into charge and motor movement during sound-evoked vibrations, revealing a process of reciprocal electro-mechanical transduction essential for tuning cochlear amplification.

biophysics↗

bioRxiv2024

Temperature-Dependent Fold-Switching Mechanism of the Circadian Clock Protein KaiB

The oscillator of the cyanobacterial circadian clock relies on the ability of the KaiB protein to switch reversibly between a stable ground-state fold (gsKaiB) and an unstable fold-switched fold (fsKaiB). Rare fold-switching events by KaiB provide a critical delay in the negative feedback loop of this post-translational oscillator. In this study, we experimentally and computationally investigate the temperature dependence of fold switching and its mechanism. We demonstrate that the stability of gsKaiB increases with temperature compared to fsKaiB and that the Q10 value for the gsKaiB [->] fsKaiB transition is nearly three times smaller than that for the reverse transition. Simulations and native-state hydrogen-deuterium exchange NMR experiments suggest that fold switching can involve both subglobally and near-globally unfolded intermediates. The simulations predict that the transition state for fold switching coincides with isomerization of conserved prolines in the most rapidly exchanging region, and we confirm experimentally that proline isomerization is a rate-limiting step for fold switching. We explore the implications of our results for temperature compensation, a hallmark of circadian clocks, through a kinetic model.

biochemistry↗

bioRxiv2023

Folding of Prestin's Anion-Binding Site and the Mechanism of Outer Hair Cell Electromotility

Prestin responds to transmembrane voltage fluctuations by changing its cross-sectional area, a process underlying the electromotility of outer hair cells and cochlear amplification. Prestin belongs to the SLC26 family of anion transporters yet is the only member capable of displaying electromotility. Prestins voltage-dependent conformational changes are driven by the putative displacement of residue R399 and a set of sparse charged residues within the transmembrane domain, following the binding of a Cl- anion at a conserved binding site formed by amino termini of the TM3 and TM10 helices. However, a major conundrum arises as to how an anion that binds in proximity to a positive charge (R399), can promote the voltage sensitivity of prestin. Using hydrogen-deuterium exchange mass spectrometry, we find that prestin displays an unstable anion-binding site, where folding of the amino termini of TM3 and TM10 is coupled to Cl- binding. This event shortens the TM3-TM10 electrostatic gap, thereby connecting the two helices, resulting in reduced cross-sectional area. These folding events upon anion-binding are absent in SLC26A9, a non-electromotile transporter closely related to prestin. Dynamics of prestin embedded in a lipid bilayer closely match that in detergent micelle, except for a destabilized lipid-facing helix TM6 that is critical to prestins mechanical expansion. We observe helix fraying at prestins anion-binding site but cooperative unfolding of multiple lipid-facing helices, features that may promote prestins fast electromechanical rearrangements. These results highlight a novel role of the folding equilibrium of the anion-binding site, and helps define prestins unique voltage-sensing mechanism and electromotility.

biophysics↗

bioRxiv2022

Sequential Activation and Local Unfolding Control Poly(A)-Binding Protein Condensation

Eukaryotic cells form biomolecular condensates to sense and adapt to their environment1,2. Poly(A)-binding protein (Pab1), a canonical stress granule marker3,4, condenses upon heat shock or starvation, promoting adaptation5. The molecular basis of condensation has remained elusive due to a dearth of techniques to probe structure directly in condensates. Here we apply hydrogen-deuterium exchange/mass spectrometry (HDX-MS) to investigate the molecular mechanism of Pab1s condensation. We find that Pab1s four RNA recognition motifs (RRMs) undergo different levels of partial unfolding upon condensation, and the changes are similar for thermal and pH stresses. Although structural heterogeneity is observed, the ability of MS to describe individual subpopulations allows us to identify which regions become partially unfolded and contribute to the condensates interaction network. Our data yield a clear molecular picture of Pab1s stress-triggered condensation, which we term sequential activation, wherein each RRM becomes activated at a temperature where it partially unfolds and associates with other likewise activated RRMs to form the condensate. This model thus implies that sequential activation is dictated by the underlying free energy surface, an effect we refer to as thermodynamic specificity. Our study represents a methodological advance for elucidating the interactions that drive biomolecular condensation that we anticipate will be widely applicable. Furthermore, our findings demonstrate how condensation can use thermodynamic specificity to perform an acute response to multiple, stresses, a potentially general mechanism for stress-responsive proteins.

biophysics↗

bioRxiv2021

Lipid Bilayer Induces Contraction of the Denatured State Ensemble of a Helical-Bundle Membrane Protein

Defining the denatured state ensemble (DSE) and intrinsically disordered proteins is essential to understanding protein folding, chaperone action, degradation, translocation and cell signaling. While a majority of studies have focused on water-soluble proteins, the DSE of membrane proteins is much less characterized. Here, we reconstituted the DSE of a helical-bundle membrane protein GlpG of Escherichia coli in native lipid bilayers and measured the DSEs conformation and compactness. The DSE was obtained using steric trapping, which couples spontaneous denaturation of a doubly biotinylated GlpG to binding of two bulky monovalent streptavidin molecules. Using limited proteolysis and mass spectrometry, we mapped the flexible regions in the DSE. Using our paramagnetic biotin derivative and double electron-electron resonance spectroscopy, we determined the dimensions of the DSE. Finally, we employed our Upside model for molecular dynamics simulations to generate the DSE including the collapsed and fully expanded states in a bilayer. We find that the DSE is highly dynamic involving the topology changes of transmembrane segments and their unfolding. The DSE is expanded relative to the native state, but only to 55-90% of the fully expanded condition. The degree of expansion depends on the chemical potential with regards to local packing and the lipid composition. Our result suggests that the E. colis native lipid bilayer promotes the association of helices in the DSE of membrane proteins and, probably in general, facilitating interhelical interactions. This tendency may be the outcome of a general lipophobic effect of proteins within the cell membranes. SignificanceHere, we delineate the conformation of the denatured state ensemble (DSE) of a membrane protein confined in a native lipid bilayer and assay whether the bilayer permits full expansion or nonspecific collapse of the DSE. Using the intramembrane protease GlpG as a model, we find that the denatured state is a dynamic ensemble involving topological changes and local unfolding of transmembrane segments. The bilayer tends to contract the DSE relative to the fully lipid-solvated, expanded conformations while the degree of compactness is determined by the balance between protein-lipid, lipid-lipid and protein-protein interactions. These findings provide new insights into the lipid bilayer as a solvent that mediates folding, chaperone action, turnover and protein-protein interactions in cell membranes.

biophysics↗

bioRxiv2019

Structural basis for adhesion G protein-coupled receptor Gpr126 function

Many drugs target the extracellular regions (ECRs) of cell-surface receptors. The large and alternatively-spliced ECRs of adhesion G protein-coupled receptors (aGPCRs) have key functions in diverse biological processes including neurodevelopment, embryogenesis, and tumorigenesis. However, their structures and mechanisms of action remain unclear, hampering drug development. The aGPCR Gpr126/Adgrg6 regulates Schwann cell myelination, ear canal formation, and heart development; and GPR126 mutations cause myelination defects in human. Here, we determine the structure of the complete zebrafish Gpr126 ECR and reveal five domains including a previously-unknown domain. Strikingly, the Gpr126 ECR adopts a closed conformation that is stabilized by an alternatively spliced linker and a conserved calcium-binding site. Alternative splicing regulates ECR conformation and receptor signaling, while mutagenesis of the newly-characterized calcium-binding site abolishes Gpr126 function in vivo. These results demonstrate that Gpr126 ECR utilizes a multi-faceted dynamic approach to regulate receptor function and provide novel insights into ECR-targeted drug design.

biochemistry↗