Microscopic processes in global relativistic jets containing helical magnetic fields

In the study of relativistic jets one of the key open questions is their interaction with the environment on the microscopic level. Here, we study the initial evolution of both electron–proton (e−–p+) and electron–positron (e±) relativistic jets containing helical magnetic fields, focusing on their interaction with an ambient plasma. We have performed simulations of “global” jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities such as the Weibel instability, the kinetic Kelvin-Helmholtz instability (kKHI) and the Mushroom instability (MI). In our initial simulation study these kinetic instabilities are suppressed and new types of instabilities can grow. In the e−–p+ jet simulation a recollimation-like instability occurs and jet electrons are strongly perturbed. In the e± jet simulation a recollimation-like instability occurs at early times followed by a kinetic instability and the general structure is similar to a simulation without helical magnetic field. Simulations using much larger systems are required in order to thoroughly follow the evolution of global jets containing helical magnetic fields

Microscopic Processes in Global Relativistic Jets Containing Helical Magnetic Fields

In the study of relativistic jets one of the key open questions is their interaction with the environment on the microscopic level. Here, we study the initial evolution of both electron–proton ( e − – p + ) and electron–positron ( e ± ) relativistic jets containing helical magnetic fields, focusing on their interaction with an ambient plasma. We have performed simulations of “global” jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities such as the Weibel instability, the kinetic Kelvin-Helmholtz instability (kKHI) and the Mushroom instability (MI). In our initial simulation study these kinetic instabilities are suppressed and new types of instabilities can grow. In the e − – p + jet simulation a recollimation-like instability occurs and jet electrons are strongly perturbed. In the e ± jet simulation a recollimation-like instability occurs at early times followed by a kinetic instability and the general structure is similar to a simulation without helical magnetic field. Simulations using much larger systems are required in order to thoroughly follow the evolution of global jets containing helical magnetic fields.This work is supported by NSF AST-0908010, AST-0908040, NASA-NNX09AD16G, NNX12AH06G, NNX13AP-21G, and NNX13AP14G grants. The work of J.N. and O.K. has been supported by Narodowe Centrum Nauki through research project DEC-2013/10/E/ST9/00662. Y.M. is supported by the ERC Synergy Grant “BlackHoleCam—Imaging the Event Horizon of Black Holes” (Grant No. 610058). M.P. acknowledges support through grant PO 1508/1-2 of the Deutsche Forschungsgemeinschaft. Simulations were performed using Pleiades and Endeavor facilities at NASA Advanced Supercomputing (NAS), and using Gordon and Comet at The San Diego Supercomputer Center (SDSC), and Stampede at The Texas Advanced Computing Center, which are supported by the NSF. This research was started during the program “Chirps, Mergers and Explosions: The Final Moments of Coalescing Compact Binaries” at the Kavli Institute for Theoretical Physics, which is supported by the National Science Foundation under grant No. PHY05-51164. The first velocity shear results using an electron positron plasma were obtained during the Summer Aspen workshop “Astrophysical Mechanisms of Particle Acceleration and Escape from the Accelerators” held at the Aspen Center for Physics (1–15 September 2013). We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI

Histones bundle F-actin filaments and affect actin structure.

Histones are small polycationic proteins complexed with DNA located in the cell nucleus. Upon apoptosis they are secreted from the cells and react with extracellular polyanionic compounds. Actin which is a polyanionic protein, is also secreted from necrotic cells and interacts with histones. We showed that both histone mixture (histone type III) and the recombinant H2A histone bundles F-actin, increases the viscosity of the F-actin containing solution and polymerizes G-actin. The histone-actin bundles are relatively insensitive to increase of ionic strength, unlike other polycation, histatin, lysozyme, spermine and LL-37 induced F-actin bundles. The histone-actin bundles dissociate completely only in the presence of 300-400 mM NaCl. DNA, which competes with F-actin for histones, disassembles histone induced actin bundles. DNase1, which depolymerizes F- to G-actin, actively unbundles the H2A histone induced but slightly affects the histone mixture induced actin bundles. Cofilin decreases the amount of F-actin sedimented by low speed centrifugation, increases light scattering and viscosity of F-actin-histone mixture containing solutions and forms star like superstructures by copolymerizing G-actin with H2A histone. The results indicate that histones are tightly attached to F-actin by strong electrostatic and hydrophobic forces. Since both histones and F-actin are present in the sputum of patients with cystic fibrosis, therefore, the formation of the stable histone-actin bundles can contribute to the pathology of this disease by increasing the viscosity of the sputum. The actin-histone interaction in the nucleus might affect gene expression

Actin and DNA protect histones from degradation by bacterial proteases but inhibit their antimicrobial activity

Histones are small polycationic proteins located in the cell nucleus. Together, DNA and histones are integral constituents of the nucleosomes. Upon apoptosis, necrosis and infection - induced cell death, histones are released from the cell. The extracellular histones have strong antimicrobial activity but are also cytotoxic and thought as mediators of cell death in sepsis. The antimicrobial activity of the cationic extracellular histones is inhibited by the polyanionic DNA and F-actin, which also become extracellular upon cell death. DNA and F-actin protect histones from degradation by the proteases of Pseudomonas aeruginosa and Porphyromonas gingivalis. However, though the integrity of the histones is protected, the activity of histones as antibacterial agents is lost. The inhibition of the histone's antibacterial activity and their protection from proteolysis by DNA and F-actin indicate a tight electrostatic interaction between the positively charged histones and negatively charged DNA and F-actin, which may have physiological significance in maintaining the equilibrium between the beneficial antimicrobial activity of extracellular histones and their cytotoxic effects

Effect of cofilin on the sedimentation of 4 μM MgF-actin bundled by histone mixture or H2A histone.

<p>(A), 2–8 μM cofilin added to 4 μM F-actin bundled by 10.5 and 63 μg/ml histone mixture or (B) by 1 μM (14 μg/ml) and 3 μM (42 μg/ml) H2A histone. (C), 42 μg/ml histone mixture or 4 μM (56 μg/ml) H2A histone and 2.5 or 5 μM cofilin were added simultaneously to 4 μM F-actin. Samples were centrifuged at 20800xg for 8 min, supernatants run on SDS-PAGE and evaluated as described in MATERIALS and METHODS. The presented data are mean and standard deviation of three independent experiments. Insets: lanes of SDS-PAGE gels, representatives of three independent experiments, obtained from SDS-PAGE of low speed centrifugation supernatants.</p

Effect of DNase1 on the light scattering and sedimentation of 4 μM MgF-actin bundled by histone mixture or H2A histone.

<p>(A) Effect of 9 μM DNase1 on the light scattering of 4 μM MgF-actin bundled by 63 μg/ml histone mixture or 3 μM (42 μg/ml) H2A histone. Light scattering change was followed as described in MATERIALS and METHODS. Presented data are representative of three independent experiments. (B). Effect of 2–15 μM DNase1 on the sedimentation of 4 μM MgF-actin bundled by 63 μg/ml histone mixture or 3 μM (42 μg/ml) H2A histone. The difference between the amount of actin sedimented following DNase1 treatment of histone mixture and H2A histone bundled actin is highly significant. Samples were centrifuged at 20800xg for 8 min, supernatants run on SDS-PAGE and evaluated as described in MATERIALS and METHODS. The presented data are mean and standard deviation of three independent experiments. Insets: actin lanes, representatives of three independent experiments, from SDS-PAGE of low speed centrifugation supernatants.</p

Effect of 3 μM (42 μg/ml) H2A histone and 6 μM cofilin on the viscosity of 4 μM MgF-actin measured by Viscous Aqua fluorescence viscosity probe.

<p>Viscous Aqua in original Ursa BioScience vial was dissolved in 50 μl methanol then diluted 50 times in actin buffer and added to actin containing solutions in 1 to 50 ratio in pH 7.4 buffer. The fluorescence of the mixtures was measured as described in MATERIALS and METHODS. The fluorescence values (in artificial units, A.U.) of the samples at 492 nm emission maximum minus the fluorescence of the buffer are given in the figure. The data obtained were compared by statistical analysis and the significance of the differences was indicated. * = p<0.05, ** = p<0.01 *** = p<0.005. The fluorescence emission increases with the increasing viscosity of the samples. The presented data are mean and standard deviation of at least three independent experiments.</p

Polymerization of CaATP-G-actin by histone mixture and H2A histone followed by high speed centrifugation was compared with the plateaus of the pyrene fluorescent measurements.

<p>(A) 5.25–63 μg/ml histone mixture, or (B) 0.5–4 μM (7–56 μg/ml) H2A histone was added to 4 μM CaATP-G-actin in pH7.4 CaATP-G-buffer. Samples were centrifuged at 129,151xg for 2h, supernatants run on SDS-PAGE and evaluated as described in MATERIALS and METHODS. Fig 2A, inset: SDS-PAGE, left, actin and histone mixture before centrifugation; right, molecular weight marker. Fig 2B, inset: actin lanes from the SDS-PAGE of supernatants after high speed centrifugation. All SDS-PAGE gels are representatives of three independent experiments. Actin sedimentation values were compared with plateaus of pyrene fluorescence upon addition of histone mixture (C) or H2A histone (D). Pyrene fluorescence values were taken from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0183760#pone.0183760.g001" target="_blank">Fig 1</a>. Sedimentation data were taken from experiments presented in Fig 2A and B. The presented data are mean and standard deviation of three independent experiments.</p

Effect of cofilin on the light scattering of histone mixture or H2A histone bundled MgF-actin.

<p>4x 2 μM cofilin was added to 4 μM MgF-actin bundled by 63 μg/ml histone mixture (A), or by 4 μM (56 μg/ml) H2A histone (B). Stars indicate addition of 2 μM cofilin. Light scattering change was followed as described in MATERIALS and METHODS. Presented data are representative of three independent experiments.</p

Histone mixture and H2A histone induced bundle formation of Mg-F-actin followed by low speed centrifugation and by light scattering.

<p>5.25–84 μg/ml histone mixture (A), or 1–4 μM (14–56 μg/ml) H2A histone (B), were added to 4 μM MgF-actin in pH7.4 F-buffer and centrifuged at low speed. Samples were centrifuged at 20,800xg for 8 min, supernatants run on SDS-PAGE and evaluated as described in MATERIALS and METHODS. The presented data are mean and standard deviation of three independent experiments. Insets: actin lanes, representatives of three independent experiments, from SDS-PAGE of low speed centrifugation supernatants. (C) 5.25–42 μg/ml histone mixture or (D) 1–4 μM (14–56 μg/ml) H2A histone were added to 4 μM MgF-actin in pH7.4 F-buffer and the light scattering change was followed as described in MATERIALS and METHODS. Presented data are representative of three independent experiments. All measurements were done at pH7.4 in F-buffer.</p