Science

Syndicate content
The best in science news, commentary, and research
Updated: 8 years 17 weeks ago

[This Week in Science] Breaking chiral symmetry in a solid

Thu, 10/22/2015 - 23:00
Author: Jelena Stajic
Categories: Journal Articles

[This Week in Science] Metered rehydration in pollen grains

Thu, 10/22/2015 - 23:00
Author: Pamela J. Hines
Categories: Journal Articles

[This Week in Science] Multifunctional root regulators

Thu, 10/22/2015 - 23:00
Author: Pamela J. Hines
Categories: Journal Articles

[This Week in Science] Early signs of dementia

Thu, 10/22/2015 - 23:00
Author: Peter Stern
Categories: Journal Articles

[This Week in Science] Observing ultrafast myoglobin dynamics

Thu, 10/22/2015 - 23:00
Author: Valda Vinson
Categories: Journal Articles

[Editors' Choice] Stay away from the light

Thu, 10/22/2015 - 23:00
Author: Sacha Vignieri
Categories: Journal Articles

[Editors' Choice] A tough shell for nanoparticles

Thu, 10/22/2015 - 23:00
Author: Phil Szuromi
Categories: Journal Articles

[Editors' Choice] Seeing through microbiome development

Thu, 10/22/2015 - 23:00
Author: Caroline Ash
Categories: Journal Articles

[Editors' Choice] Factor adjusts cell number in gut

Thu, 10/22/2015 - 23:00
Author: Beverly A. Purnell
Categories: Journal Articles

[Editors' Choice] What shape is the asteroid Juno?

Thu, 10/22/2015 - 23:00
Author: Keith T. Smith
Categories: Journal Articles

[Editors' Choice] Lab management: Lessons over 35 years

Thu, 10/22/2015 - 23:00
Author: Brad Wible
Categories: Journal Articles

[Editors' Choice] Patching up the injured heart

Thu, 10/22/2015 - 23:00
Author: Paula A. Kiberstis
Categories: Journal Articles

[Research Article] HIV-1 Nef hijacks clathrin coats by stabilizing AP-1:Arf1 polygons

Thu, 10/22/2015 - 23:00
The lentiviruses HIV and simian immunodeficiency virus (SIV) subvert intracellular membrane traffic as part of their replication cycle. The lentiviral Nef protein helps viruses evade innate and adaptive immune defenses by hijacking the adaptor protein 1 (AP-1) and AP-2 clathrin adaptors. We found that HIV-1 Nef and the guanosine triphosphatase Arf1 induced trimerization and activation of AP-1. Here we report the cryo–electron microscopy structures of the Nef- and Arf1-bound AP-1 trimer in the active and inactive states. A central nucleus of three Arf1 molecules organizes the trimers. We combined the open trimer with a known dimer structure and thus predicted a hexagonal assembly with inner and outer faces that bind the membranes and clathrin, respectively. Hexagons were directly visualized and the model validated by reconstituting clathrin cage assembly. Arf1 and Nef thus play interconnected roles in allosteric activation, cargo recruitment, and coat assembly, revealing an unexpectedly intricate organization of the inner AP-1 layer of the clathrin coat. Authors: Qing-Tao Shen, Xuefeng Ren, Rui Zhang, Il-Hyung Lee, James H. Hurley
Categories: Journal Articles

[Research Article] Structural and biochemical basis for induced self-propagation of NLRC4

Thu, 10/22/2015 - 23:00
Responding to stimuli, nucleotide-binding domain and leucine-rich repeat–containing proteins (NLRs) oligomerize into multiprotein complexes, termed inflammasomes, mediating innate immunity. Recognition of bacterial pathogens by NLR apoptosis inhibitory proteins (NAIPs) induces NLR family CARD domain–containing protein 4 (NLRC4) activation and formation of NAIP-NLRC4 inflammasomes. The wheel-like structure of a PrgJ-NAIP2-NLRC4 complex determined by cryogenic electron microscopy at 6.6 angstrom reveals that NLRC4 activation involves substantial structural reorganization that creates one oligomerization surface (catalytic surface). Once activated, NLRC4 uses this surface to catalyze the activation of an inactive NLRC4, self-propagating its active conformation to form the wheel-like architecture. NAIP proteins possess a catalytic surface matching the other oligomerization surface (receptor surface) of NLRC4 but not those of their own, ensuring that one NAIP is sufficient to initiate NLRC4 oligomerization. Authors: Zehan Hu, Qiang Zhou, Chenlu Zhang, Shilong Fan, Wei Cheng, Yue Zhao, Feng Shao, Hong-Wei Wang, Sen-Fang Sui, Jijie Chai
Categories: Journal Articles

[Report] Cryo-EM structure of the activated NAIP2-NLRC4 inflammasome reveals nucleated polymerization

Thu, 10/22/2015 - 23:00
The NLR family apoptosis inhibitory proteins (NAIPs) bind conserved bacterial ligands, such as the bacterial rod protein PrgJ, and recruit NLR family CARD-containing protein 4 (NLRC4) as the inflammasome adapter to activate innate immunity. We found that the PrgJ-NAIP2-NLRC4 inflammasome is assembled into multisubunit disk-like structures through a unidirectional adenosine triphosphatase polymerization, primed with a single PrgJ-activated NAIP2 per disk. Cryo–electron microscopy (cryo-EM) reconstruction at subnanometer resolution revealed a ~90° hinge rotation accompanying NLRC4 activation. Unlike in the related heptameric Apaf-1 apoptosome, in which each subunit needs to be conformationally activated by its ligand before assembly, a single PrgJ-activated NAIP2 initiates NLRC4 polymerization in a domino-like reaction to promote the disk assembly. These insights reveal the mechanism of signal amplification in NAIP-NLRC4 inflammasomes. Authors: Liman Zhang, Shuobing Chen, Jianbin Ruan, Jiayi Wu, Alexander B. Tong, Qian Yin, Yang Li, Liron David, Alvin Lu, Wei Li Wang, Carolyn Marks, Qi Ouyang, Xinzheng Zhang, Youdong Mao, Hao Wu
Categories: Journal Articles

[Report] Metallic ground state in an ion-gated two-dimensional superconductor

Thu, 10/22/2015 - 23:00
Recently emerging two-dimensional (2D) superconductors in atomically thin layers and at heterogeneous interfaces are attracting growing interest in condensed matter physics. Here, we report that an ion-gated zirconium nitride chloride surface, exhibiting a dome-shaped phase diagram with a maximum critical temperature of 14.8 kelvin, behaves as a superconductor persisting to the 2D limit. The superconducting thickness estimated from the upper critical fields is ≅ 1.8 nanometers, which is thinner than one unit-cell. The majority of the vortex phase diagram down to 2 kelvin is occupied by a metallic state with a finite resistance, owing to the quantum creep of vortices caused by extremely weak pinning and disorder. Our findings highlight the potential of electric-field–induced superconductivity, establishing a new platform for accessing quantum phases in clean 2D superconductors. Authors: Yu Saito, Yuichi Kasahara, Jianting Ye, Yoshihiro Iwasa, Tsutomu Nojima
Categories: Journal Articles

[Report] Evidence for the chiral anomaly in the Dirac semimetal Na3Bi

Thu, 10/22/2015 - 23:00
In a Dirac semimetal, each Dirac node is resolved into two Weyl nodes with opposite “handedness” or chirality. The two chiral populations do not mix. However, in parallel electric and magnetic fields (E||B), charge is predicted to flow between the Weyl nodes, leading to negative magnetoresistance. This “axial” current is the chiral (Adler-Bell-Jackiw) anomaly investigated in quantum field theory. We report the observation of a large, negative longitudinal magnetoresistance in the Dirac semimetal Na3Bi. The negative magnetoresistance is acutely sensitive to deviations of the direction of B from E and is incompatible with conventional transport. By rotating E (as well as B), we show that it is consistent with the prediction of the chiral anomaly. Authors: Jun Xiong, Satya K. Kushwaha, Tian Liang, Jason W. Krizan, Max Hirschberger, Wudi Wang, R. J. Cava, N. P. Ong
Categories: Journal Articles

[Report] Electron paramagnetic resonance of individual atoms on a surface

Thu, 10/22/2015 - 23:00
We combined the high-energy resolution of conventional spin resonance (here ~10 nano–electron volts) with scanning tunneling microscopy to measure electron paramagnetic resonance of individual iron (Fe) atoms placed on a magnesium oxide film. We drove the spin resonance with an oscillating electric field (20 to 30 gigahertz) between tip and sample. The readout of the Fe atom’s quantum state was performed by spin-polarized detection of the atomic-scale tunneling magnetoresistance. We determine an energy relaxation time of T1 ≈ 100 microseconds and a phase-coherence time of T2 ≈ 210 nanoseconds. The spin resonance signals of different Fe atoms differ by much more than their resonance linewidth; in a traditional ensemble measurement, this difference would appear as inhomogeneous broadening. Authors: Susanne Baumann, William Paul, Taeyoung Choi, Christopher P. Lutz, Arzhang Ardavan, Andreas J. Heinrich
Categories: Journal Articles

[Report] Direct sampling of electric-field vacuum fluctuations

Thu, 10/22/2015 - 23:00
The ground state of quantum systems is characterized by zero-point motion. This motion, in the form of vacuum fluctuations, is generally considered to be an elusive phenomenon that manifests itself only indirectly. Here, we report direct detection of the vacuum fluctuations of electromagnetic radiation in free space. The ground-state electric-field variance is inversely proportional to the four-dimensional space-time volume, which we sampled electro-optically with tightly focused laser pulses lasting a few femtoseconds. Subcycle temporal readout and nonlinear coupling far from resonance provide signals from purely virtual photons without amplification. Our findings enable an extreme time-domain approach to quantum physics, with nondestructive access to the quantum state of light. Operating at multiterahertz frequencies, such techniques might also allow time-resolved studies of intrinsic fluctuations of elementary excitations in condensed matter. Authors: C. Riek, D. V. Seletskiy, A. S. Moskalenko, J. F. Schmidt, P. Krauspe, S. Eckart, S. Eggert, G. Burkard, A. Leitenstorfer
Categories: Journal Articles

[Report] Asteroseismology can reveal strong internal magnetic fields in red giant stars

Thu, 10/22/2015 - 23:00
Internal stellar magnetic fields are inaccessible to direct observations, and little is known about their amplitude, geometry, and evolution. We demonstrate that strong magnetic fields in the cores of red giant stars can be identified with asteroseismology. The fields can manifest themselves via depressed dipole stellar oscillation modes, arising from a magnetic greenhouse effect that scatters and traps oscillation-mode energy within the core of the star. The Kepler satellite has observed a few dozen red giants with depressed dipole modes, which we interpret as stars with strongly magnetized cores. We find that field strengths larger than ~105 gauss may produce the observed depression, and in one case we infer a minimum core field strength of ≈107 gauss. Authors: Jim Fuller, Matteo Cantiello, Dennis Stello, Rafael A. Garcia, Lars Bildsten
Categories: Journal Articles