Structural mechanism of plant aquaporin gating

Plants counteract fluctuations in water supply by regulating all aquaporins in the cell plasma membrane. Channel closure results either from the dephosphorylation of two conserved serine residues under conditions of drought stress, or from the protonation of a conserved histidine residue following a drop in cytoplasmic pH due to anoxia during flooding. Here we report the X-ray structure of the spinach plasma membrane aquaporin SoPIP2;1 in its closed conformation at 2.1 A resolution and in its open conformation at 3.9 A resolution, and molecular dynamics simulations of the initial events governing gating. In the closed conformation loop D caps the channel from the cytoplasm and thereby occludes the pore. In the open conformation loop D is displaced up to 16 A and this movement opens a hydrophobic gate blocking the channel entrance from the cytoplasm. These results reveal a molecular gating mechanism which appears conserved throughout all plant plasma membrane aquaporins.     

植物水孔蛋白PIP2表达量快速无标记检测

相较于传统的抗体检测,适配体更易于大量快速合成,且可和多种检测技术相结合,在蛋白检测方面具有巨大的潜力.水孔蛋白作为生物体内水分跨膜运输的主要途径,了解其表达量的变化在植物水代谢研究中有着重要意义.利用传统的混合列分法构建了8个C端恒定半胱氨酸残基的类肽适配体文库,结合表面等离激元共振成像技术,筛选得到能特异性结合高等植物水孔蛋白PIP2的类肽适配体PPA7,其亲和力K_D高达2.52×10~(-9) mol/L.利用PPA7检测了石竹玻璃化和正常植株的水孔蛋白表达量,结果表明,石竹玻璃化植株的水孔蛋白表达量显著高于正常植株.研究提供了一种新的植物蛋白定量检测策略,也为进一步明确水孔蛋白在组培苗玻璃化发生中的作用奠定了基础.     

Low intracellular pH and chemical agents slow inactivation gating in sodium channels of muscle

Excitation of nerve or muscle requires an orderly opening and closing of molecular pores, the ionic channels, in the plasma membrane. During the action potential, Na channels are opened (activated) by the advancing wave of depolarisation, contributing a pulse of inward sodium current, and then are closed again (inactivated) by the continued depolarisation. As one approach both to obtaining molecular information on the Na channel and towards further defining the recently discovered kinetic interactions of the inactivation and activation gating steps, we have surveyed here the effects of chemical agents reported to slow or prevent Na channel inactivation. We find that many of the agents studied by others on invertebrate giant axons or vertebrate nerve act on our frog skeletal muscle preparation. In addition, we have discovered that simply lowering the intracellular pH nearly eliminates inactivation. The activation mechanism seems to resist modification.     

Functional architecture of an intracellular membrane t-SNARE

Lipid bilayer fusion is mediated by SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) located on the vesicle membrane (v-SNAREs) and the target membrane (t-SNAREs). The assembled v-SNARE/t-SNARE complex consists of a bundle of four helices, of which one is supplied by the v-SNARE and the other three by the t-SNARE. For t-SNAREs on the plasma membrane, the protein syntaxin supplies one helix and a SNAP-25 protein contributes the other two. Although there are numerous homologues of syntaxin on intracellular membranes, there are only two SNAP-25-related proteins in yeast, Sec9 and Spo20, both of which are localized to the plasma membrane and function in secretion and sporulation, respectively. What replaces SNAP-25 in t-SNAREs of intracellular membranes? Here we show that an intracellular t-SNARE is built from a 'heavy chain' homologous to syntaxin and two separate non-syntaxin 'light chains'. SNAP-25 may thus be the exception rather than the rule, having been derived from genes that encoded separate light chains that fused during evolution to produce a single gene encoding one protein with two helices.     

碱性阴离子交换膜燃料电池实验及数值模拟

针对碱性阴离子交换膜燃料电池(AEMFC)水管理开展了实验及数值模拟工作,使用Tokuyama A201膜制备并组装了实验室规模的AEMFC单电池,建立了一个基于质量守恒、组分守恒及电荷守恒的碱性阴离子交换膜燃料电池二维稳态等温模型,用于研究电池性能及内部水传输机理。通过模型计算分析电池性能及内部水传输和水分布情况,结果表明:计算预测得到的特定参数下的极化曲线趋势与单电池测试的数据吻合良好;电流密度增加会增大水从阳极到阴极的净通量,有利于阴极反应的进行;电池两极均需进气加湿,提高阳极进气湿度可以加快水从阳极到阴极的净迁移,在较高电流密度下阴极进气湿度过低对电池性能影响较大。     

Coupling of agonist binding to channel gating in an ACh-binding protein linked to an ion channel

Neurotransmitter receptors from the Cys-loop superfamily couple the binding of agonist to the opening of an intrinsic ion pore in the final step in rapid synaptic transmission. Although atomic resolution structural data have recently emerged for individual binding and pore domains, how they are linked into a functional unit remains unknown. Here we identify structural requirements for functionally coupling the two domains by combining acetylcholine (ACh)-binding protein, whose structure was determined at atomic resolution, with the pore domain from the serotonin type-3A (5-HT3A) receptor. Only when amino-acid sequences of three loops in ACh-binding protein are changed to their 5-HT3A counterparts does ACh bind with low affinity characteristic of activatable receptors, and trigger opening of the ion pore. Thus functional coupling requires structural compatibility at the interface of the binding and pore domains. Structural modelling reveals a network of interacting loops between binding and pore domains that mediates this allosteric coupling process.     

Effect of Aβ1-40 on membrane permeability and intracellular free Ca2+ of nerve cells

The effects of soluble and fibrillar Aβ1-40 on membrane permeability and intracellular free Ca2+ of nerve cells were investigated by the laser confocal microscopy. Results indicate that: i) Effects of soluble and fibrillar Aβ1-40 on cell membrane permeability are both concentration-de- pendent. Soluble Aβ1-40 increases membrane permeability only at concentration of 3 ?mol/L, while the toxic effect of fibrillar Aβ1-40 is much stronger, its evident effect begins from 1 ?mol/L. When its concentration rose to 3 ?mol/L, not only the membrane permeability increased, but also the nuclear membrane broke seriously. ii) Both soluble and fibrillar Aβ1-40 at high concentrations increased the intracellular free Ca2+, and the increased amplitudes are concentration-dependent. However, the fibrillar one induces the increase of intracellular Ca2+ much quicker and synchronously. These results indicate that some correlation exists between the neurotoxicity of high concentration soluble and fibrillar Aβ1-40 and the change of physico-chemical properties and intracellular Ca ion imbalance.     

Effect of Ab_(1-40) on membrane permeability and intracellular free Ca~(2+) of nerve cells

Alzheimers disease (AD) is a kind of progressive neurodegenerative disease, characterized by intracellularfibrillar tangles and extracellular senile plaques, the main component of the plaques are b-amyloid (Ab), composed of 3943 amino acids[1]. Glenner and Wong first isolated Ab peptide and determined the sequence in 1984, after-wards, a series of researches were done on its production, structure determination, aggregation, hydrophobicity, re-ceptor and cell toxicity. Ab is the abnormal fiss…     

Identification and role of plasma membrane aquaporin in maize root

Using antiserum against expressed aquaporin fusion protein, GST-RD28, the distribution of aquaporin in the plasma membrane of maize root protoplasts has been examined under confocal laser scanning microscopy by indirect fluorescence staining. Results indicate that there are abundant aquaporins in maize roots, which are distributed in plasma membrane unevenly. Western blotting analysis of total protein solubilized from maize root plasma membrane shows that antiserum against GST-RD28 can cross-react with one protein around 55 Ku. Another 28 ku protein can also be detected when the concentration of SDS and DTT in SDS-PAGE sample buffer is increased. The 55 and 28 ku proteins may be dimeric and monomeric of aquaporin respectively. Functional experiments show that aquaporin blocker HgCl₂ and aquaporin antiserum can suppress the swelling of maize root protoplasts in hypotonic solution, indicating that aquaporin in plasma membrane of protoplast facilitates rapid transmembrane water flow.     

突出矿煤岩微孔隙特征及其渗透特性

从煤与瓦斯突出矿采集煤样,通过扫描电镜对其微结构和孔隙裂隙特征进行了观测。利用MTS815.02型岩石力学实验系统进行了3块标准煤样全应力应变过程的电液伺服试验,给出了主应力差、煤样渗透率、非Darcy流β因子和加速度系数与轴向应变关系曲线。研究表明:该突出矿煤样结构不均一,以粒状、网状、片状结构为主,也可见到鳞片状和压扭性结构;在煤样破坏过程中,由于围压的作用,全应力应变过程中煤样的渗透率随着应变的增大而发生变化,但其变化不很显著;非Darcy流β因子和加速度系数趋势相同,非Darcy流β因子均为负值。     

Structure and gating mechanism of the acetylcholine receptor pore

The nicotinic acetylcholine receptor controls electrical signalling between nerve and muscle cells by opening and closing a gated, membrane-spanning pore. Here we present an atomic model of the closed pore, obtained by electron microscopy of crystalline postsynaptic membranes. The pore is shaped by an inner ring of 5 alpha-helices, which curve radially to create a tapering path for the ions, and an outer ring of 15 alpha-helices, which coil around each other and shield the inner ring from the lipids. The gate is a constricting hydrophobic girdle at the middle of the lipid bilayer, formed by weak interactions between neighbouring inner helices. When acetylcholine enters the ligand-binding domain, it triggers rotations of the protein chains on opposite sides of the entrance to the pore. These rotations are communicated through the inner helices, and open the pore by breaking the girdle apart.     

Rapid evolutionary innovation during an Archaean genetic expansion

The natural history of Precambrian life is still unknown because of the rarity of microbial fossils and biomarkers. However, the composition of modern-day genomes may bear imprints of ancient biogeochemical events. Here we use an explicit model of macroevolution including gene birth, transfer, duplication and loss events to map the evolutionary history of 3,983 gene families across the three domains of life onto a geological timeline. Surprisingly, we find that a brief period of genetic innovation during the Archaean eon, which coincides with a rapid diversification of bacterial lineages, gave rise to 27% of major modern gene families. A functional analysis of genes born during this Archaean expansion reveals that they are likely to be involved in electron-transport and respiratory pathways. Genes arising after this expansion show increasing use of molecular oxygen (P = 3.4 × 10(-8)) and redox-sensitive transition metals and compounds, which is consistent with an increasingly oxygenating biosphere.     

离子液体调控超导研究

载流子在超导材料中扮演关键角色,其浓度调控对研究超导特性及相关量子器件至关重要.然而载流子浓度通常与其他自由度相互耦合,难以做到单一物理量变化,例如,化学掺杂同时会导致晶格等发生变化.最近迅速发展的离子液体调控技术,兼具了传统的化学掺杂和场效应晶体管优点——大范围、原位、可逆地调节载流子浓度.随着这项技术的发展,逐渐演变出两类调控思路:静电场效应和电化学调控.本文从这两个方面,回顾了离子液体调控在诱导新奇超导态和调控高温超导薄膜物性上的应用:静电场效应对绝缘或半导体体系十分有效,而对于本身载流子浓度较高的材料(如高温超导体等),电化学调控则发挥了重要作用.离子液体因其强大的原位调控能力和易于与其他手段结合的特点,正逐渐成为超导研究中不可或缺的手段,在构建精确相图、突破高温超导机理等方面发挥不可替代的作用.     

Midzone activation of aurora B in anaphase produces an intracellular phosphorylation gradient

Proper partitioning of the contents of a cell between two daughters requires integration of spatial and temporal cues. The anaphase array of microtubules that self-organize at the spindle midzone contributes to positioning the cell-division plane midway between the segregating chromosomes. How this signalling occurs over length scales of micrometres, from the midzone to the cell cortex, is not known. Here we examine the anaphase dynamics of protein phosphorylation by aurora B kinase, a key mitotic regulator, using fluorescence resonance energy transfer (FRET)-based sensors in living HeLa cells and immunofluorescence of native aurora B substrates. Quantitative analysis of phosphorylation dynamics, using chromosome- and centromere-targeted sensors, reveals that changes are due primarily to position along the division axis rather than time. These dynamics result in the formation of a spatial phosphorylation gradient early in anaphase that is centred at the spindle midzone. This gradient depends on aurora B targeting to a subpopulation of microtubules that activate it. Aurora kinase activity organizes the targeted microtubules to generate a structure-based feedback loop. We propose that feedback between aurora B kinase activation and midzone microtubules generates a gradient of post-translational marks that provides spatial information for events in anaphase and cytokinesis.     

Rapid spread of an inherited incompatibility factor in California Drosophila

In Drosophila simulans in California, an inherited cytoplasmic incompatibility factor reduces egg hatch when infected males mate with uninfected females. The infection is spreading at a rate of more than 100 km per year; populations in which the infection was rare have become almost completely infected within three years. Analyses of the spread using estimates of selection in the field suggest dispersal distances far higher than those found by direct observation of flies. Hence, occasional long-distance dispersal, possibly coupled with local extinction and recolonization, may be important to the dynamics. Incompatibility factors that can readily spread through natural populations may be useful for population manipulation and important as a post-mating isolating mechanism.     

特低渗砂岩储层临界启动渗透率分析

根据特低渗油藏启动压力梯度的概念提出了临界启动渗透率概念.以鄂尔多斯盆地延长组特低渗砂岩储层岩心实验结果为基础,得到了拟启动压力梯度与储层渗透率之间的关系,建立了注采井间驱动压力梯度的变化规律分析.根据拟启动压力梯度与驱动压力梯度的关系,给出了临界启动渗透率的计算方法,以及注采井间临界启动渗透率的变化规律.结果表明,拟启动压力梯度的变化存在临界点;注、采井附近临界启动渗透率下限最低;在两井间中心附近临界启动渗透率下限达到最大.可见,建立有效的驱替压力系统,增大注采井间驱动压力梯度,降低临界启动渗透率,是实现特低渗储层高效开发的主要措施.     

Aun+1-1、AunCr-1 (n=1~10)团簇结构、稳定性与电子构型研究

采用密度泛函理论对阴离子团簇Au_(n+1)~(-1)、Au_nCr~(-1)(n=1～10)的基态结构、稳定性、电子构型与磁性做了系统研究。结果表明:Au_(n+1)~(-1)均为平面构型,Au_nCr~(-1)(n=1～6)为平面结构,Au_nCr~(-1)(n=7～10)为体结构;Au_(n+1)~(-1)替代掺杂Cr原子提高团簇的稳定性;离解能与二阶差分能结果表明偶数的Au_(n+1)~(-1)、Au_nCr~(-1)稳定性比相邻奇数团簇高;轨道的有效电荷分布结果说明Cr原子的掺入使得Au原子内部spd杂化变得更复杂,Au_nCr~(-1)中Cr原子成为价电荷的主要接受者;轨道磁矩分布结果则表明Au_(n+1)~(-1)电子结构随尺寸增长表现为明显的开闭壳层结构,Au_nCr~(-1)的电子结构均为开壳层,Au_(n+1)~(-1)的磁矩主要由Au 5d轨道贡献,而Au_nCr~(-1)的磁矩则主要由Cr 3d轨道贡献。