Biology subjects

Newcombe, E. A.

Publications and source records attributed to Newcombe, E. A..

5 recordsLinked to original sources

bioRxiv2024

The importance of stereochemistry in the disorder-order continuum of protein-protein interactions

Intrinsically disordered proteins can bind via the formation of highly disordered protein complexes without the formation of 3D-structure. Most naturally occurring proteins are "left-handed" or levorotatory (L), made up only of L-amino acids, imprinting molecular structure and communication with stereochemistry. In contrast, their mirror image "right-handed" or dextrorotatory (D) amino acids are rare in Nature. Whether disordered protein complexes are truly independent of 3D-topology and thus of chiral constraints is not clear. To test the chiral constraints of disordered protein-protein interactions, a set of interacting protein pairs covering the disorder-order continuum was chosen as representative examples. By observing both the natural ligands and their stereochemical mirror images in free and bound states, we discovered that chirality was inconsequential in a fully disordered complex. However, if the interaction relied on the ligand undergoing coupled folding and binding, correct stereochemistry was essential. Between these extremes, binding could be observed for the D-ligand with a strength that correlated with the amount of disorder in the final complex. These findings have important implications for our understanding of protein-protein interactions, the molecular processes leading to complex formation, the use of D-peptides in drug discovery, and the chemistry of protein evolution of the first living entities on Earth.

biophysics↗

bioRxiv2022

Deciphering the alphabet of disorder -- Glu and Asp act differently on local but not global properties

Compared to folded proteins, the sequences of intrinsically disordered proteins (IDPs) are enriched in polar and charged amino acids. Glutamate is one of the most enriched amino acids in IDPs, while the chemically similar amino acid aspartate is less enriched. So far, the underlying functional differences of glutamates and aspartates in IDPs remain poorly understood. In this study, we examine the differential effects of aspartate and glutamates in IDPs by comparing the function and conformational ensemble of glutamate and aspartate variants of the disordered protein Dss1, using a range of assays, including interaction studies, nuclear magnetic resonance spectroscopy, small angle X-ray scattering and molecular dynamics simulation. First, we analyze the sequences of the rapidly growing data base of experimentally verified IDPs (DisProt) and show that the glutamate enrichment is not caused by a taxonomy bias in IDPs. From analyses of local and global structural properties as well as cell growth and protein-protein interactions using a model acidic IDP from yeast and three Glu/Asp variants, we find that while Glu/Asp support similar function and global dimensions, the variants differ in their binding affinities and population of local transient structural elements. We speculate that these local structural differences may play roles in functional diversity where glutamates can support increased helicity important for folding and binding, while aspartates support extended structures and form helical caps, as well as playing more relevant roles in e.g., transactivation domains and ion-binding.

biophysics↗

bioRxiv2022

Assessment of models for calculating the hydrodynamic radius of intrinsically disordered proteins

Diffusion measurements by pulsed field gradient NMR and fluorescence correlation spectroscopy can be used to probe the hydrodynamic radius of proteins, which contains information about the overall dimension of a protein in solution. The comparison of this value with structural models of intrinsically disordered proteins is nonetheless impaired by the uncertainty of the accuracy of the methods for computing the hydrodynamic radius from atomic coordinates. To tackle this issue, we here build conformational ensembles of 11 intrinsically disordered proteins that we ensure are in agreement with measurements of compaction by small-angle X-ray scattering. We then use these ensembles to identify the forward model that more closely fits the radii derived from pulsed field gradient NMR diffusion experiments. Of the models we examined, we find that the Kirkwood-Riseman equation provides the best description of the hydrodynamic radius probed by pulsed field gradient NMR experiments. While some minor discrepancies remain, our results enable better use of measurements of the hydrodynamic radius in integrative modelling and for force field benchmarking and parameterization. SIGNIFICANCEAccurate models of the conformational properties of intrinsically disordered proteins rely on our ability to interpret experimental data that reports on the conformational ensembles of these proteins in solution. Methods to calculate experimental observables from conformational ensembles are central to link experiments and computation, for example in integrative modelling or the assessment of molecular force fields. Benchmarking such methods is, however, difficult for disordered proteins because it is difficult to construct accurate ensembles without using the data. We here circumvent this problem by combining independent measures of protein compaction to test several methods to calculate the hydrodynamic radius of a disordered protein, as measured by pulsed field gradient NMR diffusion experiments, and find the Kirkwood-Riseman model to be most accurate.

biophysics↗

bioRxiv2021

Refinement of α-synuclein ensembles against SAXS data: Comparison of force fields and methods

The inherent flexibility of intrinsically disordered proteins (IDPs) makes it difficult to interpret experimental data using structural models. On the other hand, molecular dynamics simulations of IDPs often suffer from force-field inaccuracies, and long simulations times or enhanced sampling methods are needed to obtain converged ensembles. Here, we apply metainference and Bayesian/Maximum Entropy reweighting approaches to integrate prior knowledge of the system with experimental data, while also dealing with various sources of errors and the inherent conformational heterogeneity of IDPs. We have measured new SAXS data on the protein -synuclein, and integrate this with simulations performed using different force fields. We find that if the force field gives rise to ensembles that are much more compact than what is implied by the SAXS data it is difficult to recover a reasonable ensemble. On the other hand, we show that when the simulated ensemble is reasonable, we can obtain an ensemble that is consistent with the SAXS data, but also with NMR diffusion and paramagnetic relaxation enhancement data.

biophysics↗

bioRxiv2017

Tadpole-like conformations of huntingtin exon 1 with expanded polyglutamine engenders novel interactions in cells

Soluble huntingtin exon 1 (Httex1) with expanded polyglutamine (polyQ) engenders neurotoxicity in Huntingtons disease. To uncover the physical basis of this toxicity, we performed structural studies of soluble Httex1 for wild type and mutant polyQ lengths. Nuclear magnetic resonance experiments show evidence for conformational rigidity across the polyQ region. In contrast, hydrogen-deuterium exchange shows absence of backbone amide protection, suggesting negligible persistence of hydrogen bonds. The seemingly conflicting results are explained by all-atom simulations, which show that Httex1 adopts tadpole-like structures with a globular head encompassing the N-terminal amphipathic and polyQ regions and the tail encompassing the C-terminal proline-rich region. The surface area of the globular domain increases monotonically with polyQ length. This stimulates sharp increases in gain-of-function interactions in cells for expanded polyQ, and one of these interactions is with the stress-granule protein Fus. Our results highlight plausible connections between Httex1 structure and routes to neurotoxicity.

biochemistry↗