PaperPlayer biorxiv biophysics

Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.09.243030v1?rss=1

Authors: Tesei, G., Martins, J. M., Kunze, M. B. A., Wang, Y., Crehuet, R., Lindorff-Larsen, K.

Abstract:

Owing to their plasticity, intrinsically disordered and multidomain proteins require descriptions based on multiple conformations, thus calling for techniques and analysis tools that are capable of dealing with conformational ensembles rather than a single protein structure. Here, we introduce DEER-PREdict, a software to predict Double Electron-Electron Resonance distance distributions as well as Paramagnetic Relaxation Enhancement rates from ensembles of protein conformations. DEER-PREdict uses an established rotamer library approach to describe the paramagnetic probes which are bound covalently to the protein. DEER-PREdict has been designed to operate efficiently on large conformational ensembles, such as those generated by molecular dynamics simulation, to facilitate the validation or refinement of molecular models as well as the interpretation of experimental data. The performance and accuracy of the software is demonstrated with experimentally characterized protein systems: HIV-1 protease, T4 Lysozyme and Acyl-CoA-binding protein. DEER-PREdict is open source (GPLv3) and available at https://github.com/KULL-Centre/DEERpredict and as a Python PyPI package https://pypi.org/project/DEERPREdict.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.10.244491v1?rss=1

Authors: Alfieri, A., Gaska, I., Forth, S.

Abstract:

The proper structural organization of the microtubule-based spindle during cell division requires the collective activity of many different types of proteins. These include non-motor microtubule-associated proteins (MAPs) whose functions include crosslinking microtubules to regulate filament sliding rates and assembling microtubule arrays. One such protein is PRC1, an essential MAP that has been shown to preferentially crosslink overlapping antiparallel microtubules at the spindle midzone. PRC1 has been proposed to act as a molecular brake, but insight into the mechanism of how PRC1 molecules function cooperatively to resist motor-driven microtubule sliding and to allow for the formation of stable midzone overlaps has been lacking. Here we employ a modified microtubule gliding assay to rupture PRC1-mediated microtubule pairs using surface-bound kinesins. We discovered that PRC1 crosslinks always reduce bundled filament sliding velocities relative to single microtubule gliding rates, and do so via two distinct emergent modes of mechanical resistance to motor-driven sliding. We term these behaviors braking and coasting, where braking events exhibit substantially slowed microtubule sliding compared to coasting events. Strikingly, braking behavior requires the formation of two distinct high-density clusters of PRC1 molecules near microtubule tips. Our results suggest a cooperative mechanism for PRC1 accumulation when under mechanical load that leads to a unique state of enhanced resistance to filament sliding and provides insight into collective protein ensemble behavior in regulating the mechanics of spindle assembly.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.10.241752v1?rss=1

Authors: Blackwell, T. J., Stump, W. T., Clippinger, S. R., Greenberg, M. J.

Abstract:

Molecular motors couple chemical transitions to conformational changes that perform mechanical work in a wide variety of biological processes. Disruption of this coupling can lead to diseases, and therefore there is a need to accurately measure mechanochemical coupling in motors in both health and disease. Optical tweezers, with nanometer spatial and millisecond temporal resolution, have provided valuable insights into these processes. However, fluctuations due to Brownian motion can make it difficult to precisely resolve these conformational changes. One powerful analysis technique that has improved our ability to accurately measure mechanochemical coupling in motor proteins is ensemble averaging of individual trajectories. Here, we present a user-friendly computational tool, Software for Precise Analysis of Single Molecules (SPASM), for generating ensemble averages of single-molecule data. This tool utilizes several conceptual advances, including optimized procedures for identifying single-molecule interactions and the implementation of a change point algorithm, to more precisely resolve molecular transitions. Using both simulated and experimental data, we demonstrate that these advances allow for accurate determination of the mechanics and kinetics of the myosin working stroke with a smaller set of data. Importantly, we provide our open source MATLAB-based program with a graphical user interface that enables others to readily apply these advances to the analysis of their own data.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.07.241299v1?rss=1

Authors: Chattopadhyay, K., Sannigrahi, A., Bandyopadhyay, A.

Abstract:

Understanding of prion aggregation in membrane environment may help to ameliorate neurodegenerative complications caused by the amyloid forms of prions. Here, we investigated the membrane binding induced aggregation of yeast prion protein Sup35. Using the combination of fluorescence correlation spectroscopy (FCS) at single molecule resolution and other biophysical studies, we establish that lipid composition and lipid/protein ratio are key modulators of the aggregation kinetics of Sup35. In the presence of zwitterionic membrane, Sup35 exhibited a novel biphasic aggregation kinetics at lipid/protein ratio ranging between 20:1 and 70:1 (termed here as the Optimum Lipid Concentration, OLC). In ratios below (Low Lipid Concentration, LLC) and above (ELC, Excess Lipid Concentration) that range, the aggregation was found to be monophasic. In contrast, in the presence of negatively charged membrane, we did not observe any bi-phasic aggregation kinetics in the entire range of protein to lipid ratios. The toxicity of the aggregates formed within OLC range was found to be greater. Our results provide a mechanistic description of the role that membrane-concentration/composition-modulated-aggregation may play in neurodegenerative diseases.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.07.241463v1?rss=1

Authors: Tassis, K., Vietrov, R., Koning, M. d., de Boer, M., Gouridis, G., Cordes, T.

Abstract:

The current model of active transport via ABC importers is mostly based on structural, biochemical and genetic data. We here establish single-molecule Foerster-resonance energy transfer (smFRET) assays to monitor the conformational states and heterogeneity of the type-I ABC importer OpuA from Lactococcus lactis. Our studies include intradomain assays that elucidate conformational changes within the substrate-binding domain (SBD) OpuAC and interdomain assays between SBDs or transmembrane domains. Using the methodology, we studied ligand-binding mechanisms as well as ATP and glycine betaine dependences of conformational changes. Our study expands the scope of smFRET investigations towards a class of so far unstudied ABC importers, and paves the way for a full understanding of their transport cycle in the future.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.07.241042v1?rss=1

Authors: Negrete, J., Lengyel, I. M., Rohde, L., Desai, R. A., Oates, A. C., Julicher, F.

Abstract:

We present a general theory of noisy genetic oscillators with externally regulated production rate. The observables that characterize the genetic oscillator are discussed, and it is shown how their statistics depend on the statistics of the external regulator. We show that these observables have generic features that are observed in two different experimental systems: the expression of the circadian clock genes in fibroblasts, and in the transient and oscillatory dynamics of the segmentation clock genes observed in cells disassociated from zebrafish embryos. Our work shows that genetic oscillations with diverse biological contexts can be understood in a common framework based on delayed negative feedback system, and slow regulator dynamics.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.07.234443v1?rss=1

Authors: Chaves-Arquero, B., Martinez-Lumbreras, S., Sibille, N., Camero, S., Bernado, P., Jimenez, M. A., Zorrilla, S., Perez-Canadillas, J. M.

Abstract:

Yeast eIF4G1 interacts with RNA binding proteins (RBPs) like Pab1 and Pub1 affecting its function in translation initiation and stress granules formation. We present an NMR and SAXS study of the intrinsically disordered region of eIF4G1, eIF4G11-249, and its interactions with Pub1 and Pab1. The conformational ensemble of eIF4G11-249 shows an -helix within the BOX3 conserved element and a dynamic network of fuzzy {pi}-{pi} and {pi}-cation interactions involving arginine and aromatic residues. The Pab1 RRM2 domain interacts with eIF4G1 BOX3, the canonical interaction site, but also with BOX2, a conserved element of unknown function to date. In contrast, the Pub1 RRM3 domain interacts with the RNA1-1 and BOX1 regions of eIF4G1. Mixtures of Pub1, Pab1 and eIF4G1 form micrometer-size protein condensates that require the presence of the eIF4G1 BOX1 element. These homotypic interactions suggest a double key mechanism of eIF4G1 regulation, important for understanding the architecture of stress granule cores.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.07.236406v1?rss=1

Authors: Raveendran, M., Leach, A. R., Hopes, T. S., Aspden, J., Actis, P.

Abstract:

Nanopores hold great potential for the analysis of complex biological molecules at the single entity level. One particularly interesting macromolecular machine is the ribosome, responsible for translating mRNA into proteins. In this study, we use a solid-state nanopore to fingerprint 80S ribosomes and polysomes from a human neuronal cell line and, Drosophila melanogaster cultured cells and ovaries. Specifically, we show that the peak amplitude and dwell time characteristics of 80S ribosomes are distinct from polysomes and can be used to discriminate ribosomes from polysomes in mixed samples. Moreover, we are able to distinguish large polysomes, containing more than 7 ribosomes, from those containing 2-3 ribosomes, and demonstrate a correlation between polysome size and peak amplitude. This study highlights the application of solid-state nanopores as a rapid analytical tool for the detection and characterization of ribosomal complexes.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.05.237966v1?rss=1

Authors: Lin, Y., Fichou, Y., Longhini, A. P., Llanes, L. C., Yin, Y., Bazan, G. C., Kosik, K. S., Han, S.

Abstract:

Amyloid aggregation of tau protein is implicated in neurodegenerative diseases, yet its facilitating factors are poorly understood. Recently, tau has been shown to undergo liquid liquid phase separation (LLPS) both in vivo and in vitro. LLPS was shown to facilitate tau amyloid aggregation in certain cases, while independent of aggregation in other cases. It is therefore important to understand the differentiating properties that resolve this apparent conflict. We report on a model system of hydrophobically driven LLPS induced by high salt concentration (LLPS-HS), and compare it to electrostatically driven LLPS represented by tau-RNA/heparin complex coacervation (LLPS-ED). We show that LLPS-HS promotes tau protein dehydration, undergoes maturation and directly leads to canonical tau fibrils, while LLPS-ED is reversible, remains hydrated and does not promote amyloid aggregation. We show that the nature of the interaction driving tau condensation is the differentiating factor between aggregation-prone and aggregation-independent LLPS.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.05.238170v1?rss=1

Authors: Sun, Y., Yue, H., Copos, C., Zhu, K., Zhang, Y., Gao, X., Sun, Y., Reid, B., Lin, F., Zhao, M., Mogilner, A.

Abstract:

Motile cells migrate directionally in the electric field in a process known as galvanotaxis. Galvanotaxis is important in wound healing, development, cell division, and nerve growth. Different cell types migrate in opposite directions in electric fields, to either cathode, or anode, and the same cell can switch the directionality depending on chemical conditions. We previously reported that individual fish keratocyte cells sense electric fields and migrate to the cathode, while inhibition of PI3K reverses single cells to the anode. Many physiological processes rely on collective, not individual, cell migration, so here we report on directional migration of cohesive cell groups in electric fields. Uninhibited cell groups of any size move to the cathode, with speed decreasing and directionality increasing with the group size. Surprisingly, large groups of PI3K-inhibited cells move to the cathode, in the direction opposite to that of individual cells, which move to the anode, while such small groups are not persistently directional. In the large groups, cells' velocities are distributed unevenly: the fastest cells are at the front of the uninhibited groups, but at the middle and rear of the PI3K-inhibited groups. Our results are most consistent with the hypothesis, supported by the computational model, that cells inside and at the edge of the groups interpret directional signals differently. Namely, cells in the group interior are directed to the cathode independently of their chemical state. Meanwhile, edge cells behave like the individual cells: they are directed to the cathode/anode in uninhibited/PI3K-inhibited groups, respectively. As a result, all cells drive uninhibited groups to the cathode, but a mechanical tug-of-war between the inner and edge cells directs large PI3K-inhibited groups with cell majority in the interior to the cathode, while rendering small groups non-directional.

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