Biology subjects

Estelle, A.

Publications and source records attributed to Estelle, A..

4 recordsLinked to original sources

bioRxiv2026

NMR-measured Per-residue Electrostatic Potentials Reveal the Importance of Arginine-Lysine Balance on the Conformational Ensemble of Disordered Histone H3 Tails in Nucleosome Core Particles

Biophysical studies of chromatin have provided key insights into how the genome is regulated. Many atomic resolution structures of the fundamental building block of chromatin, the nucleosome core particle (NCP), as well as larger NCP arrays, both in isolation and in complex with effectors, or with post-translational modifications, have been elucidated. These provide in-depth pictures of key functional interactions. Considerably less information is available on the intrinsically disordered nucleosome tails that are critically important for higher order interactions in chromatin, and for transcription, DNA repair, and phase separation, and that serve as hubs for post-translational modifications. Here we focus on the tail of one of the four histones, histone-3 (H3), and measure electrostatic potentials at each of its amide proton positions in isolated NCPs via solution NMR spectroscopy. Using these potentials, in concert with molecular dynamics simulations, an ensemble of structures is calculated for WT H3 tails, as well as variants where all tail arginines are replaced by lysines (R2K) or vice versa (K2R). Our ensembles reveal that K2R tails have a higher propensity to occupy the most negatively charged region of the NCP between the DNA gyres than R2K or WT tails, while lysine enriched tails have an increased relative preference for the less negative regions near the DNA entry and exit points. The structural ensembles provide insight into differences in interactions between neighboring particles that lead to changes in diffusion and phase separation propensities between the NCP variants.

biophysics↗

bioRxiv2025

Weak Motifs, Strong Complex: KANK1 Uses Cooperative Multivalency with the Hub-Protein LC8 to Bridge Cytoskeletal Complexes

The cortically anchored adaptor KANK1 organizes microtubules at focal adhesions through a long, intrinsically disordered linker (L2), yet how this linker spans the [~]35-50 nm membrane-microtubule gap is unclear. Here, we combine in-cell, biochemical, and biophysical assays, predictions of motif interaction and multivalent assembly using AlphaFold, and structural analysis by electron microscopy to show that the hub protein LC8, which binds more than 100 clients, converts the intrinsically disordered 600 amino acid L2 into an elongated, multivalent, rod-like assembly. In contrast, isolated motif peptides fail to bind LC8 at physiologically relevant concentrations, indicating that strong complex formation arises from cooperativity among multiple weak sites. These results establish LC8 as a molecular switch that rigidifies and extends KANK1 L2 via distributed weak motifs and short linkers. This interaction produces compositionally homogeneous yet conformationally adaptable rods, long enough to bridge the membrane-microtubule gap, resolving the paradox. This work expands the LC8 binding repertoire, reveals design principles for multivalent assembly, and suggests a generalizable strategy for tuning length, rigidity, and flexibility in large protein architectures.

biophysics↗

bioRxiv2022

Genetic encoding of 3-nitro-tyrosine reveals the impacts of 14-3-3 nitration on client binding and dephosphorylation

14-3-3 proteins are central hub regulators of hundreds of phosphorylated "client" proteins. They are subject to over 60 post-translational modifications (PTMs), yet little is known how these PTMs alter 14-3-3 function and its ability to regulate downstream signaling pathways. An often neglected, but well documented 14-3-3 PTM found under physiological and immune-stimulatory conditions is the conversion of tyrosine to 3-nitro-tyrosine at several Tyr sites, two of which are located at sites considered important for 14-3-3 function: Y130 ({beta}-isoform numbering) is located in the primary phospho-client peptide binding groove, while Y213 is found on a secondary binding site that engages with clients for full 14-3-3/client complex formation and client regulation. By genetically encoding 3-nitro-tyrosine, we sought to understand if nitration at Y130 and Y213 effectively modulated 14-3-3 structure, function, and client complexation. The 1.5 [A] resolution crystal structure of 14-3-3 nitrated at Y130 showed the nitro group altered the conformation of key residues in the primary binding site, while functional studies confirmed client proteins failed to bind this variant of 14-3-3. But, in contrast to other client-binding deficient variants, it did not localize to the nucleus. The 1.9 [A] resolution structure of 14-3-3 nitrated at Y213 revealed unusual flexibility of its C-terminal -helix resulting in domain swapping, suggesting additional structural plasticity though its relevance is not clear as this nitrated form retained its ability to bind clients. Collectively, our data suggest nitration of 14-3-3 will alter downstream signaling systems, and if uncontrolled could result in global dysregulation of the 14-3-3 interactome.

biochemistry↗

bioRxiv2020

Automated and statistically corrected identification of flexible multivalent IDP-bound assemblies in electron micrographs

Multivalent intrinsically disordered protein (IDP) complexes are prevalent in biology and control diverse cellular functions, including tuning levels of transcription, coordinating cell-signaling events, and regulating the assembly and disassembly of complex macromolecular architectures. These systems pose a significant challenge to structural investigation, due to the continuum dynamics imparted by the IDP and compositional heterogeneity resulting from characteristic low-affinity interactions. Traditional single-particle electron microscopy (EM) is a powerful tool for visualizing IDP complexes. However, the IDPs themselves are typically "invisible" by EM, undermining methods of image analysis and structural interpretation. To overcome these challenges, we developed a pipeline for automated analysis of common beads-on-a-string type of assemblies, composed of IDPs bound at multivalent sites to the ubiquitous ~20 kDa cross-linking hub protein LC8. This approach quantifies conformational and compositional heterogeneity on a single-particle basis, and statistically corrects spurious observations arising from random proximity of bound and unbound LC8. After careful validation of the methodology, the approach was applied to the nuclear pore IDP Nup159 and the transcription factor ASCIZ. The analysis unveiled significant compositional and conformational diversity in both systems that could not be obtained from traditional single particle EM class-averaging strategies, and shed new light on how these architectural properties contribute to their physiological roles in supramolecular assembly and transcriptional regulation. Ultimately, we expect that this approach may be adopted to many other intrinsically disordered systems that have evaded traditional methods of structural characterization. Significance StatementIntrinsically disordered proteins (IDPs) or protein regions (IDRs) represent >30% of the human proteome, but mechanistically remain some of the most poorly understood classes of proteins in biology. This dearth in understanding stems from these very same intrinsic and dynamic properties, which make them difficult targets for quantitative and structural characterization. Here, we present an automated approach for extracting quantitative descriptions of conformational and compositional heterogeneity present in a common beads-on-a-string type of multivalent IDP system from single-particle images in electron micrographs. This promising approach may be adopted to many other intrinsically disordered systems that have evaded traditional ensemble methods of characterization.

biophysics↗