1
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Micheletti C, Chubak I, Orlandini E, Smrek J. Topology-Based Detection and Tracking of Deadlocks Reveal Aging of Active Ring Melts. ACS Macro Lett 2024:124-129. [PMID: 38198592 PMCID: PMC10883035 DOI: 10.1021/acsmacrolett.3c00567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2024]
Abstract
Connecting the viscoelastic behavior of stressed ring melts to the various forms of entanglement that can emerge in such systems is still an open challenge. Here, we consider active ring melts, where stress is generated internally, and introduce a topology-based method to detect and track consequential forms of ring entanglements, namely, deadlocks. We demonstrate that, as stress accumulates, more and more rings are co-opted in a growing web of deadlocks that entrap many other rings by threading, bringing the system to a standstill. The method ought to help the study of topological aging in more general polymer contexts.
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Affiliation(s)
- Cristian Micheletti
- Scuola Internazionale Superiore di Studi Avanzati (SISSA), Via Bonomea 265, I-34136 Trieste, Italy
| | - Iurii Chubak
- Sorbonne Université CNRS, Physico-Chimie des électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France
| | - Enzo Orlandini
- Università degli studi di Padova, Dipartimento di Fisica "G. Galilei", Via Marzolo 8, I-35100 Padova, Italy
| | - Jan Smrek
- Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria
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2
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Bhat MI, Sharma P, Sitharam TG, Murthy TG. Force transmission during repose of flexible granular chains. SOFT MATTER 2023; 19:8493-8506. [PMID: 37723876 DOI: 10.1039/d3sm00526g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/20/2023]
Abstract
We study the mechanics of standing columns formed during the repose of flexible granular chains. It is one of the many intriguing behaviours exhibited by granular materials when links capable of transmitting tension exist between particles. We develop and calibrate a discrete element method contact model to simulate the mechanics of the macroscopic flexible granular chains and conduct simulations of the angle of repose experiments of these chains by extracting a chain-filled cylinder and allowing the material to flow out under gravity and repose. We evaluate various micro-mechanical, topological and macroscopic parameters to elucidate the mechanics of the repose behaviour of chain ensembles. It is the ability of the links connecting the individual particles to transmit tensile forces along the chain backbone that provides lateral stability to the column, enabling them to stand. In particular, the contact force rearrangement inside the columns generates a self-confining radial stress near the base of the columns, which provides an important stabilizing stress.
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3
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Chang R, Prakash M. Topological damping in an ultrafast giant cell. Proc Natl Acad Sci U S A 2023; 120:e2303940120. [PMID: 37792511 PMCID: PMC10576051 DOI: 10.1073/pnas.2303940120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Accepted: 09/01/2023] [Indexed: 10/06/2023] Open
Abstract
Cellular systems are known to exhibit some of the fastest movements in biology, but little is known as to how single cells can dissipate this energy rapidly and adapt to such large accelerations without disrupting internal architecture. To address this, we investigate Spirostomum ambiguum-a giant cell (1-4 mm in length) well-known to exhibit ultrafast contractions (50% of body length) within 5 ms with a peak acceleration of 15[Formula: see text]. Utilizing transmitted electron microscopy and confocal imaging, we identify an association of rough endoplasmic reticulum (RER) and vacuoles throughout the cell-forming a contiguous fenestrated membrane architecture that topologically entangles these two organelles. A nearly uniform interorganelle spacing of 60 nm is observed between RER and vacuoles, closely packing the entire cell. Inspired by the entangled organelle structure, we study the mechanical properties of entangled deformable particles using a vertex-based model, with all simulation parameters matching 10 dimensionless numbers to ensure dynamic similarity. We demonstrate how entangled deformable particles respond to external loads by an increased viscosity against squeezing and help preserve spatial relationships. Because this enhanced damping arises from the entanglement of two networks incurring a strain-induced jamming transition at subcritical volume fractions, which is demonstrated through the spatial correlation of velocity direction, we term this phenomenon "topological damping." Our findings suggest a mechanical role of RER-vacuolar meshwork as a metamaterial capable of damping an ultrafast contraction event.
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Affiliation(s)
- Ray Chang
- Department of Bioengineering, Stanford University, Palo Alto, CA94305
| | - Manu Prakash
- Department of Bioengineering, Stanford University, Palo Alto, CA94305
- Woods Institute for the Environment, Stanford University, Palo Alto, CA94305
- Chan Zuckerberg Biohub, San Francisco, CA94158
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4
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Patil VP, Tuazon H, Kaufman E, Chakrabortty T, Qin D, Dunkel J, Bhamla MS. Ultrafast reversible self-assembly of living tangled matter. Science 2023; 380:392-398. [PMID: 37104611 DOI: 10.1126/science.ade7759] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Abstract
Tangled active filaments are ubiquitous in nature, from chromosomal DNA and cilia carpets to root networks and worm collectives. How activity and elasticity facilitate collective topological transformations in living tangled matter is not well understood. We studied California blackworms (Lumbriculus variegatus), which slowly form tangles in minutes but can untangle in milliseconds. Combining ultrasound imaging, theoretical analysis, and simulations, we developed and validated a mechanistic model that explains how the kinematics of individual active filaments determines their emergent collective topological dynamics. The model reveals that resonantly alternating helical waves enable both tangle formation and ultrafast untangling. By identifying generic dynamical principles of topological self-transformations, our results can provide guidance for designing classes of topologically tunable active materials.
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Affiliation(s)
- Vishal P Patil
- Department of Bioengineering, Stanford University, 475 Via Ortega, Stanford, CA 94305, USA
| | - Harry Tuazon
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30318, USA
| | - Emily Kaufman
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30318, USA
| | - Tuhin Chakrabortty
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30318, USA
| | - David Qin
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - Jörn Dunkel
- Department of Mathematics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
| | - M Saad Bhamla
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30318, USA
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5
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Barkataki K, Panagiotou E. The Jones polynomial of collections of open curves in 3-space. Proc Math Phys Eng Sci 2022. [DOI: 10.1098/rspa.2022.0302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Measuring the entanglement complexity of collections of open curves in 3-space has been an intractable, yet pressing mathematical problem, relevant to a plethora of physical systems, such as in polymers and biopolymers. In this manuscript, we give a novel definition of the Jones polynomial that generalizes the classic Jones polynomial to collections of open curves in 3-space. More precisely, first we provide a novel definition of the Jones polynomial of linkoids (open link diagrams) and show that this is a well-defined single variable polynomial that is a topological invariant, which, for link-type linkoids, coincides with that of the corresponding link. Using the framework introduced in (Panagiotou E, Kauffman L. 2020
Proc. R. Soc. A
476
, 20200124. ((
doi:10.1098/rspa.2020.0124
)), this enables us to define the Jones polynomial of collections of open and closed curves in 3-space. For collections of open curves in 3-space, the Jones polynomial has real coefficients and it is a continuous function of the curves’ coordinates. As the endpoints of the curves tend to coincide, the Jones polynomial tends to that of the resultant link. We demonstrate with numerical examples that the novel Jones polynomial enables us to characterize the topological/geometrical complexity of collections of open curves in 3-space for the first time.
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Affiliation(s)
- Kasturi Barkataki
- School of Mathematical and Statistical Sciences, Arizona State University, Tempe, AZ 85287-1804, USA
| | - Eleni Panagiotou
- Department of Mathematics and SimCenter, University of Tennessee at Chattanooga, 613 McCallie Avenue, Chattanooga,TN 37403, USA
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6
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Guo F, Wu J, Yang Z, Li K, Zhang L. Penetration of linear chains into semiflexible knotted rings in linear-ring blends. POLYMER 2022. [DOI: 10.1016/j.polymer.2022.125248] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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7
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Baldwin Q, Sumpter B, Panagiotou E. The Local Topological Free Energy of the SARS-CoV-2 Spike Protein. Polymers (Basel) 2022; 14:polym14153014. [PMID: 35893978 PMCID: PMC9332627 DOI: 10.3390/polym14153014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Revised: 07/15/2022] [Accepted: 07/19/2022] [Indexed: 02/04/2023] Open
Abstract
The novel coronavirus SARS-CoV-2 infects human cells using a mechanism that involves binding and structural rearrangement of its Spike protein. Understanding protein rearrangement and identifying specific amino acids where mutations affect protein rearrangement has attracted much attention for drug development. In this manuscript, we use a mathematical method to characterize the local topology/geometry of the SARS-CoV-2 Spike protein backbone. Our results show that local conformational changes in the FP, HR1, and CH domains are associated with global conformational changes in the RBD domain. The SARS-CoV-2 variants analyzed in this manuscript (alpha, beta, gamma, delta Mink, G614, N501) show differences in the local conformations of the FP, HR1, and CH domains as well. Finally, most mutations of concern are either in or in the vicinity of high local topological free energy conformations, suggesting that high local topological free energy conformations could be targets for mutations with significant impact of protein function. Namely, the residues 484, 570, 614, 796, and 969, which are present in variants of concern and are targeted as important in protein function, are predicted as such from our model.
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Affiliation(s)
- Quenisha Baldwin
- Department of Biology, Tuskegee University, Tuskegee, AL 36088, USA;
| | - Bobby Sumpter
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA;
| | - Eleni Panagiotou
- Department of Mathematics and SimCenter, University of Tennessee at Chattanooga, Chattanooga, TN 37403, USA
- Correspondence: or
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8
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Albarqi HA, Alqahtani AA, Ullah I, Khan NR, Basit HM, Iftikhar T, Wahab A, Ali M, Badar M. Microwave-Assisted Physically Cross-Linked Chitosan-Sodium Alginate Hydrogel Membrane Doped with Curcumin as a Novel Wound Healing Platform. AAPS PharmSciTech 2022; 23:72. [PMID: 35147834 DOI: 10.1208/s12249-022-02222-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Accepted: 01/17/2022] [Indexed: 11/30/2022] Open
Abstract
This project purposes to develop chitosan and sodium alginate-based hydrogel membranes loaded with curcumin through microwave-based physical cross-linking technique and its evaluation for wound healing potential. For the purpose, curcumin-loaded chitosan and sodium alginate membranes were developed using microwave at fixed frequency of 2450 MHz, power 350 W for 60 s, and tested for their physicochemical attributes like swelling, erosion, surface morphology, drug content, and in vitro drug release. The membranes were also subjected to tensile strength and vibrational and thermal analysis followed by testing in vivo on animals. The results indicated that microwave treatment significantly enhanced the swelling ability, reduced the erosion, and ensured smooth surface texture with optimal drug content. The drug was released in a slow fashion releasing total of 41 ± 4.2% within 24-h period with a higher tensile strength of 16.4 ± 5.3 Mpa. The vibrational analysis results revealed significant fluidization of hydrophilic domains and defluidization of hydrophobic domains which translated into a significant rise in the melting temperature and corresponding enthalpy which were found to be 285.2 ± 3.2 °C and 4.89 ± 1.4 J/g. The in vivo testing revealed higher percent re-epithelialization (75 ± 2.3%) within 14 days of the treatment application in comparison to only gauze and other treatments applied, with higher extent of collagen deposition having well-defined epidermis and stratum corneum formation. The microwave-treated chitosan-sodium alginate hydrogel membranes loaded with curcumin may prove to be another alternative to treat skin injuries. Graphical Abstract.
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9
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Hagita K, Murashima T, Ogino M, Omiya M, Ono K, Deguchi T, Jinnai H, Kawakatsu T. Efficient compressed database of equilibrated configurations of ring-linear polymer blends for MD simulations. Sci Data 2022; 9:40. [PMID: 35136085 PMCID: PMC8825841 DOI: 10.1038/s41597-022-01138-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Accepted: 12/21/2021] [Indexed: 11/18/2022] Open
Abstract
To effectively archive configuration data during molecular dynamics (MD) simulations of polymer systems, we present an efficient compression method with good numerical accuracy that preserves the topology of ring-linear polymer blends. To compress the fraction of floating-point data, we used the Jointed Hierarchical Precision Compression Number - Data Format (JHPCN-DF) method to apply zero padding for the tailing fraction bits, which did not affect the numerical accuracy, then compressed the data with Huffman coding. We also provided a dataset of well-equilibrated configurations of MD simulations for ring-linear polymer blends with various lengths of linear and ring polymers, including ring complexes composed of multiple rings such as polycatenane. We executed 109 MD steps to obtain 150 equilibrated configurations. The combination of JHPCN-DF and SZ compression achieved the best compression ratio for all cases. Therefore, the proposed method enables efficient archiving of MD trajectories. Moreover, the publicly available dataset of ring-linear polymer blends can be employed for studies of mathematical methods, including topology analysis and data compression, as well as MD simulations. Measurement(s) | equilibrated configurations of ring-linear polymer blends | Technology Type(s) | molecular dynamics simulation | Factor Type(s) | length of linear and ring polymer |
Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.18742097
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Affiliation(s)
- Katsumi Hagita
- Department of Applied Physics, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka, 239-8686, Japan.
| | - Takahiro Murashima
- Department of Physics, Tohoku University, 6-3, Aramaki-aza-Aoba, Aoba-ku, Sendai, 980-8578, Japan
| | - Masao Ogino
- Faculty of Informatics, Daido University, 10-3 Takiharu-cho, Minami-ku, Nagoya, 457-8530, Japan
| | - Manabu Omiya
- Information Initiative Center, Hokkaido University, Kita 11, Nishi 5, Kita-ku, Sapporo, 060-0811, Japan
| | - Kenji Ono
- Research Institute for Information Technology, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
| | - Tetsuo Deguchi
- Department of Physics, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo, 112-8610, Japan
| | - Hiroshi Jinnai
- Institute of Multidisciplinary for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
| | - Toshihiro Kawakatsu
- Department of Physics, Tohoku University, 6-3, Aramaki-aza-Aoba, Aoba-ku, Sendai, 980-8578, Japan
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10
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Bakar BFA, Kamke FA. Alkali Concentration and Diluent Effects on Properties of Grape Cane Fiber-Reinforced Polymer Composites. Polymers (Basel) 2021; 13:polym13234055. [PMID: 34883559 PMCID: PMC8658761 DOI: 10.3390/polym13234055] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 10/15/2021] [Accepted: 10/16/2021] [Indexed: 11/16/2022] Open
Abstract
The main objective of this study was to investigate the properties of polymer composites reinforced with grape cane fibers. The fibers were subjected to a sodium hydroxide (NaOH) treatment at two treatment concentrations to extract the fibers as well as fiber surface treatment. Panels were fabricated by hand lay-up and compression molding according to different fiber types, namely outer bark (OB) and whole (W) fibers. The whole fiber was a mixture of OB and inner bark (IB) fibers. Grape cane fibers were used as the reinforcement material for unsaturated polyester (UPE) resin panels. Acrylated epoxidized soybean oil (AESO) was used as a reactive diluent material with the UPE resin, and the results were compared with panels prepared with commercial styrene-UPE. There were inconsistent alkali treatment concentration effects on the mechanical properties and water absorption. However, panels fabricated with the whole bark fibers that have been treated with 1 wt % NaOH and had AESO-UPE resin resulted in the best tensile and flexural strength.
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Affiliation(s)
- Balkis F. A. Bakar
- Department of Wood and Fiber Industry, Faculty of Forestry and Environment, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia
- Correspondence:
| | - Frederick A. Kamke
- Wood Science and Engineering, College of Forestry, Oregon State University, Corvallis, OR 97333, USA;
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11
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Orlandini E, Micheletti C. Topological and physical links in soft matter systems. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 34:013002. [PMID: 34547745 DOI: 10.1088/1361-648x/ac28bf] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Accepted: 09/21/2021] [Indexed: 06/13/2023]
Abstract
Linking, or multicomponent topological entanglement, is ubiquitous in soft matter systems, from mixtures of polymers and DNA filaments packedin vivoto interlocked line defects in liquid crystals and intertwined synthetic molecules. Yet, it is only relatively recently that theoretical and experimental advancements have made it possible to probe such entanglements and elucidate their impact on the physical properties of the systems. Here, we review the state-of-the-art of this rapidly expanding subject and organize it as follows. First, we present the main concepts and notions, from topological linking to physical linking and then consider the salient manifestations of molecular linking, from synthetic to biological ones. We next cover the main physical models addressing mutual entanglements in mixtures of polymers, both linear and circular. Finally, we consider liquid crystals, fluids and other non-filamentous systems where topological or physical entanglements are observed in defect or flux lines. We conclude with a perspective on open challenges.
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Affiliation(s)
- Enzo Orlandini
- Department of Physics and Astronomy, University of Padova and Sezione INFN, Via Marzolo 8, Padova, Italy
| | - Cristian Micheletti
- SISSA, International School for Advanced Studies, via Bonomea 265, Trieste, Italy
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12
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Panagiotou E, Kauffman LH. Vassiliev measures of complexity of open and closed curves in 3-space. Proc Math Phys Eng Sci 2021. [DOI: 10.1098/rspa.2021.0440] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In this article, we define Vassiliev measures of complexity for open curves in 3-space. These are related to the coefficients of the enhanced Jones polynomial of open curves in 3-space. These Vassiliev measures are continuous functions of the curve coordinates; as the ends of the curve tend to coincide, they converge to the corresponding Vassiliev invariants of the resulting knot. We focus on the second Vassiliev measure from the enhanced Jones polynomial for closed and open curves in 3-space. For closed curves, this second Vassiliev measure can be computed by a Gauss code diagram and it has an integral formulation, the double alternating self-linking integral. The double alternating self-linking integral is a topological invariant of closed curves and a continuous function of the curve coordinates for open curves in 3-space. For polygonal curves, the double alternating self-linking integral obtains a simpler expression in terms of geometric probabilities.
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Affiliation(s)
- Eleni Panagiotou
- Department of Mathematics and SimCenter, University of Tennessee at Chattanooga, Chattanooga, TN 37403, USA
| | - Louis H. Kauffman
- Department of Mathematics, Statistics and Computer Science, University of Illinois at Chicago, Chicago, IL 60607, USA
- Department of Mechanics and Mathematics, Novosibirsk State University, Novosibirsk, Russia
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13
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Herschberg T, Carrillo JMY, Sumpter BG, Panagiotou E, Kumar R. Topological Effects Near Order–Disorder Transitions in Symmetric Diblock Copolymer Melts. Macromolecules 2021. [DOI: 10.1021/acs.macromol.1c00780] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Tom Herschberg
- Department of Computer Science and Engineering, University of Tennessee at Chattanooga, Chattanooga, Tennessee 37403, United States
| | - Jan-Michael Y. Carrillo
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Bobby G. Sumpter
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Eleni Panagiotou
- Department of Mathematics, University of Tennessee at Chattanooga, Chattanooga, Tennessee 37403, United States
| | - Rajeev Kumar
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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14
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Najafi S, Lin Y, Longhini AP, Zhang X, Delaney KT, Kosik KS, Fredrickson GH, Shea J, Han S. Liquid-liquid phase separation of Tau by self and complex coacervation. Protein Sci 2021; 30:1393-1407. [PMID: 33955104 PMCID: PMC8197434 DOI: 10.1002/pro.4101] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Revised: 05/01/2021] [Accepted: 05/04/2021] [Indexed: 12/11/2022]
Abstract
The liquid-liquid phase separation (LLPS) of Tau has been postulated to play a role in modulating the aggregation property of Tau, a process known to be critically associated with the pathology of a broad range of neurodegenerative diseases including Alzheimer's Disease. Tau can undergo LLPS by homotypic interaction through self-coacervation (SC) or by heterotypic association through complex-coacervation (CC) between Tau and binding partners such as RNA. What is unclear is in what way the formation mechanisms for self and complex coacervation of Tau are similar or different, and the addition of a binding partner to Tau alters the properties of LLPS and Tau. A combination of in vitro experimental and computational study reveals that the primary driving force for both Tau CC and SC is electrostatic interactions between Tau-RNA or Tau-Tau macromolecules. The liquid condensates formed by the complex coacervation of Tau and RNA have distinctly higher micro-viscosity and greater thermal stability than that formed by the SC of Tau. Our study shows that subtle changes in solution conditions, including molecular crowding and the presence of binding partners, can lead to the formation of different types of Tau condensates with distinct micro-viscosity that can coexist as persistent and immiscible entities in solution. We speculate that the formation, rheological properties and stability of Tau droplets can be readily tuned by cellular factors, and that liquid condensation of Tau can alter the conformational equilibrium of Tau.
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Affiliation(s)
- Saeed Najafi
- Department of Chemistry and BiochemistryUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
- Materials Research LaboratoryUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Yanxian Lin
- Department of Biomolecular Science and EngineeringUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Andrew P. Longhini
- Molecular, Cell and Developmental BiologyUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Xuemei Zhang
- Neuroscience Research Institute, University of California Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Kris T. Delaney
- Materials Research LaboratoryUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Kenneth S. Kosik
- Molecular, Cell and Developmental BiologyUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
- Neuroscience Research Institute, University of California Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Glenn H. Fredrickson
- Materials Research LaboratoryUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
- Department of Chemical EngineeringUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Joan‐Emma Shea
- Department of Chemistry and BiochemistryUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
- Department of PhysicsUniversity of California at Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Songi Han
- Department of Chemistry and BiochemistryUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
- Neuroscience Research Institute, University of California Santa BarbaraSanta BarbaraCaliforniaUSA
- Department of Chemical EngineeringUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
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15
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Panagiotou E, Kauffman LH. Knot polynomials of open and closed curves. Proc Math Phys Eng Sci 2020; 476:20200124. [PMID: 32922152 DOI: 10.1098/rspa.2020.0124] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Accepted: 07/01/2020] [Indexed: 01/05/2023] Open
Abstract
In this manuscript, we introduce a method to measure entanglement of curves in 3-space that extends the notion of knot and link polynomials to open curves. We define the bracket polynomial of curves in 3-space and show that it has real coefficients and is a continuous function of the curve coordinates. This is used to define the Jones polynomial in a way that it is applicable to both open and closed curves in 3-space. For open curves, the Jones polynomial has real coefficients and it is a continuous function of the curve coordinates and as the endpoints of the curve tend to coincide, the Jones polynomial of the open curve tends to that of the resulting knot. For closed curves, it is a topological invariant, as the classical Jones polynomial. We show how these measures attain a simpler expression for polygonal curves and provide a finite form for their computation in the case of polygonal curves of 3 and 4 edges.
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Affiliation(s)
- Eleni Panagiotou
- Department of Mathematics and SimCenter, University of Tennessee at Chattanooga, Chattanooga, TN 37403, USA
| | - Louis H Kauffman
- Department of Mathematics, Statistics and Computer Science University of Illinois at Chicago, Chicago, IL 60607-7045, USA.,Department of Mechanics and Mathematics, Novosibirsk State University, Novosibirsk, Russia
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16
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Grønbæk C, Hamelryck T, Røgen P. GISA: using Gauss Integrals to identify rare conformations in protein structures. PeerJ 2020; 8:e9159. [PMID: 32566389 PMCID: PMC7293858 DOI: 10.7717/peerj.9159] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Accepted: 04/18/2020] [Indexed: 12/13/2022] Open
Abstract
The native structure of a protein is important for its function, and therefore methods for exploring protein structures have attracted much research. However, rather few methods are sensitive to topologic-geometric features, the examples being knots, slipknots, lassos, links, and pokes, and with each method aimed only for a specific set of such configurations. We here propose a general method which transforms a structure into a ”fingerprint of topological-geometric values” consisting in a series of real-valued descriptors from mathematical Knot Theory. The extent to which a structure contains unusual configurations can then be judged from this fingerprint. The method is not confined to a particular pre-defined topology or geometry (like a knot or a poke), and so, unlike existing methods, it is general. To achieve this our new algorithm, GISA, as a key novelty produces the descriptors, so called Gauss integrals, not only for the full chains of a protein but for all its sub-chains. This allows fingerprinting on any scale from local to global. The Gauss integrals are known to be effective descriptors of global protein folds. Applying GISA to sets of several thousand high resolution structures, we first show how the most basic Gauss integral, the writhe, enables swift identification of pre-defined geometries such as pokes and links. We then apply GISA with no restrictions on geometry, to show how it allows identifying rare conformations by finding rare invariant values only. In this unrestricted search, pokes and links are still found, but also knotted conformations, as well as more highly entangled configurations not previously described. Thus, an application of the basic scan method in GISA’s tool-box revealed 10 known cases of knots as the top positive writhe cases, while placing at the top of the negative writhe 14 cases in cis-trans isomerases sharing a spatial motif of little secondary structure content, which possibly has gone unnoticed. Possible general applications of GISA are fold classification and structural alignment based on local Gauss integrals. Others include finding errors in protein models and identifying unusual conformations that might be important for protein folding and function. By its broad potential, we believe that GISA will be of general benefit to the structural bioinformatics community. GISA is coded in C and comes as a command line tool. Source and compiled code for GISA plus read-me and examples are publicly available at GitHub (https://github.com).
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Affiliation(s)
- Christian Grønbæk
- Department of Biology, University of Copenhagen, Copenhagen, Denmark.,Current affiliation: Department of Biology, Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
| | - Thomas Hamelryck
- Department of Biology, Department of Computer Science, University of Copenhagen, Copenhagen, Denmark
| | - Peter Røgen
- DTU COMPUTE, Technical University of Denmark, Kgs. Lyngby, Denmark
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Ahmad R, Paul S, Basu S. Characterization of entanglements in glassy polymeric ensembles using the Gaussian linking number. Phys Rev E 2020; 101:022503. [PMID: 32168721 DOI: 10.1103/physreve.101.022503] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Accepted: 01/21/2020] [Indexed: 11/06/2022]
Abstract
We propose a method for enumerating entanglements between long chained, linear polymers that is based on the Gaussian linking number. The linking number is calculated between closely approaching segments of the macromolecular chains. Topological features of an entanglement, i.e., the extent to which one open segment winds around another, are reflected by the linking number. We show that using this measure, we can track disentanglement events through a deformation history and gain insights into how large scale disentanglements lead to failure. Incorporating an additional step where the topological entanglements identified along each chain are optimally clustered using standard clustering algorithms, we can also obtain a measure of the average number of rheological constraints that exist along each chain in an ensemble. Comparisons with other methods of enumerating entanglements, especially the primitive path analysis, are also made. Our results indicate that the linking number between two entangled segments in the undeformed state is a good indicator of the strength of the entanglement. Also, disentanglements occurring overwhelmingly around chain ends are an important cause of failure when a triaxial stress state exists in the polymer.
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Affiliation(s)
- Rasool Ahmad
- Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, Uttar Pradesh, India
| | - Saptarshi Paul
- Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, Uttar Pradesh, India
| | - Sumit Basu
- Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, Uttar Pradesh, India
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Kröger M. Developments in Polymer Theory and Simulation. Polymers (Basel) 2019; 12:polym12010030. [PMID: 31877990 PMCID: PMC7023532 DOI: 10.3390/polym12010030] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Accepted: 12/19/2019] [Indexed: 11/16/2022] Open
Affiliation(s)
- Martin Kröger
- Polymer Physics, Department of Materials, ETH Zurich, Leopold-Ruzicka-Weg 4, CH-8093 Zurich, Switzerland
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