Aggregation and vesiculation of membrane proteins by curvature-mediated interactions

Membrane remodelling plays an important role in cellular tasks such as endocytosis, vesiculation and protein sorting, and in the biogenesis of organelles such as the endoplasmic reticulum or the Golgi apparatus. It is well established that the remodelling process is aided by specialized proteins that can sense as well as create membrane curvature, and trigger tubulation when added to synthetic liposomes. Because the energy needed for such large-scale changes in membrane geometry significantly exceeds the binding energy between individual proteins and between protein and membrane, cooperative action is essential. It has recently been suggested that curvature-mediated attractive interactions could aid cooperation and complement the effects of specific binding events on membrane remodelling. But it is difficult to experimentally isolate curvature-mediated interactions from direct attractions between proteins. Moreover, approximate theories predict repulsion between isotropically curving proteins. Here we use coarse-grained membrane simulations to show that curvature-inducing model proteins adsorbed on lipid bilayer membranes can experience attractive interactions that arise purely as a result of membrane curvature. We find that once a minimal local bending is realized, the effect robustly drives protein cluster formation and subsequent transformation into vesicles with radii that correlate with the local curvature imprint. Owing to its universal nature, curvature-mediated attraction can operate even between proteins lacking any specific interactions, such as newly synthesized and still immature membrane proteins in the endoplasmic reticulum.     

Aerobic bacterial pyrite oxidation and acid rock drainage during the Great Oxidation Event

The enrichment of redox-sensitive trace metals in ancient marine sedimentary rocks has been used to determine the timing of the oxidation of the Earth's land surface. Chromium (Cr) is among the emerging proxies for tracking the effects of atmospheric oxygenation on continental weathering; this is because its supply to the oceans is dominated by terrestrial processes that can be recorded in the Cr isotope composition of Precambrian iron formations. However, the factors controlling past and present seawater Cr isotope composition are poorly understood. Here we provide an independent and complementary record of marine Cr supply, in the form of Cr concentrations and authigenic enrichment in iron-rich sedimentary rocks. Our data suggest that Cr was largely immobile on land until around 2.48?Gyr ago, but within the 160?Myr that followed--and synchronous with independent evidence for oxygenation associated with the Great Oxidation Event (see, for example, refs 4-6)--marked excursions in Cr content and Cr/Ti ratios indicate that Cr was solubilized at a scale unrivalled in history. As Cr isotope fractionations at that time were muted, Cr must have been mobilized predominantly in reduced, Cr(III), form. We demonstrate that only the oxidation of an abundant and previously stable crustal pyrite reservoir by aerobic-respiring, chemolithoautotrophic bacteria could have generated the degree of acidity required to solubilize Cr(III) from ultramafic source rocks and residual soils. This profound shift in weathering regimes beginning at 2.48?Gyr ago constitutes the earliest known geochemical evidence for acidophilic aerobes and the resulting acid rock drainage, and accounts for independent evidence of an increased supply of dissolved sulphate and sulphide-hosted trace elements to the oceans around that time. Our model adds to amassing evidence that the Archaean-Palaeoproterozoic boundary was marked by a substantial shift in terrestrial geochemistry and biology.     

Performing Phenomenology: Negotiating Presence in Intermedial Theatre

This paper analyzes from a pragmatic postphenomenological point of view the performative practice of CREW, a multi-disciplinary team of artists and researchers. It is our argument that this company, in its use of new immersive technologies in the context of a live stage, gives rise to a dialectics between an embodied and a disembodied perspective towards the perceived world. We will focus on W (Double U), a collaborative interactive performance, where immersive technology is used for live exchange of vision. By means of a head mounted omni-directional camera and display the fields of vision of two participants are swapped, which enables the participants to perceive the world through another person??s point of view. This intermedial experience brings a classic dichotomic perception of space to falter: material reality as a ??live?? condition can no longer be opposed to a virtual mediated reality. In the shifting moment between the embodied and the perceived world, on the fracture between what one sees and what one feels, the distinction between live and mediated is blurred, moreover, can no longer be made. The perception of the body is pushed to the extreme, causing a most confusing corporal awareness, a condition that intensifies the experience and causes an altered sense of presence. In a dynamic cognitive negotiation, one tends, however, to unify the divergent ontologies of the ??real?? and the ??virtual?? to a meaningful experience. In this respect, we refer to recent neurological experiments such as the ??rubber hand illusion?? in order to clarify the spectator??s tendency to fuse both ontologies and to embody a coherent image-world.     

智能现场仪表在水库大坝自动化系统中应用

传感器的选用是对水库大坝渗漏进行长期监测的关键技术之一，对Endress Hauser公司的DB53型静压式液位传感器的传感原理、特殊封装结构、技术特点及现场应用情况作了详细分析，同时对这种现场总线型智能化仪表使用的现场总线技术Profibus-PA基础作了介绍。采用智能现场总线仪表的南城子水库自动化系统，可靠性和自动化程度大大提高，这对大坝安全和库区调度决策将起到重要的作用。     

An improved spatially aware routing algorithm for mobile ad hoc network in inter-vehicle communication

A new algorithm called spatially aware routing algorithm with enhanced learning (SAREL) is proposed to guarantee the rationality of route selecting in inter-vehicle communication scenario. Firstly, the traffic model is discussed and set up by using Poisson distribution. Then we analyze the process of traffic evaluation with enhanced learning, and exploit movement estimation to assist state memorization. The improvement of algorithm is provided at last compared with our previous work. Simulation results show that SAREL algorithm could achieve better performance in packet delivery ratio, especially when network connection ratio is average.     

NMR analysis of a 900K GroEL GroES complex

Biomacromolecular structures with a relative molecular mass (M(r)) of 50,000 to 100,000 (50K 100K) have been generally considered to be inaccessible to analysis by solution NMR spectroscopy. Here we report spectra recorded from bacterial chaperonin complexes ten times this size limit (up to M(r) 900K) using the techniques of transverse relaxation-optimized spectroscopy and cross-correlated relaxation-enhanced polarization transfer. These techniques prevent deterioration of the NMR spectra by the rapid transverse relaxation of the magnetization to which large, slowly tumbling molecules are otherwise subject. We tested the resolving power of these techniques by examining the isotope-labelled homoheptameric co-chaperonin GroES (M(r) 72K), either free in solution or in complex with the homotetradecameric chaperonin GroEL (M(r) 800K) or with the single-ring GroEL variant SR1 (M(r) 400K). Most amino acids of GroES show the same resonances whether free in solution or in complex with chaperonin; however, residues 17 32 show large chemical shift changes on binding. These amino acids belong to a mobile loop region of GroES that forms contacts with GroEL. This establishes the utility of these techniques for solution NMR studies that should permit the exploration of structure, dynamics and interactions in large macromolecular complexes.