Structure and mechanism of the lactose permease of Escherichia coli

Membrane transport proteins that transduce free energy stored in electrochemical ion gradients into a concentration gradient are a major class of membrane proteins. We report the crystal structure at 3.5 angstroms of the Escherichia coli lactose permease, an intensively studied member of the major facilitator superfamily of transporters. The molecule is composed of N- and C-terminal domains, each with six transmembrane helices, symmetrically positioned within the permease. A large internal hydrophilic cavity open to the cytoplasmic side represents the inward-facing conformation of the transporter. The structure with a bound lactose homolog, beta-D-galactopyranosyl-1-thio-beta-D-galactopyranoside, reveals the sugar-binding site in the cavity, and residues that play major roles in substrate recognition and proton translocation are identified. We propose a possible mechanism for lactose/proton symport (co-transport) consistent with both the structure and a large body of experimental data.     

Ionic mechanism of cholinergic inhibition in molluscan neurons

Acetylcholine, the inhibitory transmitter to the so-called H-neurons of molluscs, produces its effect by increasing the permeability of the subsynaptic membrane to chloride ions. The change in permeability gives rise to a net influx of this anion, which hyperpolarizes the neuron. The presence of an outward pump of chloride ions is postulated to account for the required electrochemical gradient. The participation of potassium ions in this inhibitory phenomenon was not detected.     

茶树根系跨膜主动吸收氟的表观特征

为研究茶树根系跨膜主动吸收氟的过程,采用溶液培养法分析了茶树吸收氟的动力学特性,探究了温度、代谢抑制剂和氯离子等因素对茶树根系主动吸收氟的影响。结果表明,浓度吸收试验可用Michaelis-Menten动力学模型拟合,获得动力学参数Vmax=13.9μg·h~(-1)·g~(-1)(根干重,DW),Km=0.59 mmol·L~(-1)。与在25℃培养条件下相比,低温处理(4℃)明显抑制了茶树对氟的吸收,抑制率达到49.75%。代谢抑制剂2,4-Dinitrophenol(2,4-DNP)、叠氮钠(NaN_3)和正钒酸钠(Na_3VO_4)均抑制了茶树根系对氟的吸收过程,而且随着代谢抑制剂处理浓度的增加,茶树根系氟含量和累积量也随之不断减少。在2,4-DNP、叠氮钠和正钒酸钠浓度分别为2、0.2mmol·L~(-1)和0.6 mmol·L~(-1)条件下,茶树根系氟含量分别比对照减少了16.1%、39.1%和20.6%。当营养液中氟和氯浓度均为5 mmol·L~(-1)时,氯离子显著抑制了茶树对氟的吸收,抑制率达到73.1%,存在拮抗作用。从表观上分析,茶树根系对氟的吸收是一个与跨质膜电化学势梯度、代谢能量和载体蛋白有关的主动运输过程。     

Identification and Functional Analysis on Abiotic Stress Response of SoybeanCl-Channel Gene GmCLCnt

The Cl^- homeostasis was known as the major mechanism of soybean to achieve NaCl tolerance, but studies on the role of chloride channel under abiotic stress were relatively few. We cloned a putative CLC-type chloride channel gene GmCLCnt from soybean via RACE and it was predicted to encode a protein of 783 amino acids with 9 possible transmembrane domains and 2 tandem CBS domains. Real-time RT-PCR analysis showed that the GmCLCnt gene was expressed in all tissues of soybean but enriched in leaves and its expression was induced by NaCl, polyethylene glycol （PEG）, coldness and ABA treatments. The Arabidopsis seedlings overexpressing GmCLCnt were more tolerant to higher concentration of NaCl than those of wild type. The results suggested that the GmCLCnt may be a CLC-type chloride channel and play an important role in salt tolerance.     

Structure of the cytochrome b6f complex of oxygenic photosynthesis: tuning the cavity

The cytochrome b6f complex provides the electronic connection between the photosystem I and photosystem II reaction centers of oxygenic photosynthesis and generates a transmembrane electrochemical proton gradient for adenosine triphosphate synthesis. A 3.0 angstrom crystal structure of the dimeric b6f complex from the thermophilic cyanobacterium Mastigocladus laminosus reveals a large quinone exchange cavity, stabilized by lipid, in which plastoquinone, a quinone-analog inhibitor, and a novel heme are bound. The core of the b6f complex is similar to the analogous respiratory cytochrome bc1 complex, but the domain arrangement outside the core and the complement of prosthetic groups are strikingly different. The motion of the Rieske iron-sulfur protein extrinsic domain, essential for electron transfer, must also be different in the b6f complex.     

朱砂叶螨谷氨酸门控氯离子通道GluCl1基因的克隆与序列特征分析

朱砂叶螨是一种分布广泛、危害极大、难以防治和易产生抗性的农业害螨。为了研究朱砂叶螨杀螨剂神经靶标谷氨酸门控氯离子通道,进一步确定阿维菌素对朱砂叶螨的抗性机理,采用同源基因克隆以及RACE技术,克隆朱砂叶螨杀螨剂靶标谷氨酸门控氯离子通道(GluCl1)基因全长,分析其序列特征。结果表明,GluCl1基因序列全长为1856 bp,其中开放阅读框(ORF)为1338 bp,编码455个氨基酸,N端含25个氨基酸的信号肽,有4个跨膜结构域,GenBank登陆号为KC543353。同源比对分析表明,朱砂叶螨与其他蜱螨目GluCl基因有高度的同源性,特别与二斑叶螨的相似度最高。研究还发现朱砂叶螨敏感品系GluCl1第3个跨膜区的G314,与二斑叶螨敏感品系相应位点的氨基酸G323一致,而二斑叶螨抗性品系相应位点突变为D323。本研究进一步证实了G323突变为D323和二斑叶螨对阿维菌素产生抗性有关。本研究为今后建立以朱砂叶螨谷氨酸门控氯离子通道为靶点的选择性杀螨剂体外筛选体系奠定坚实基础。     

氯离子诱导的钢筋混凝土结构耐久性研究

从影响氯离子传输的因素、临界氯离子浓度、氯离子向混凝土内传输的机理、氯离子传输预测模型等方面对因氯离子诱导的钢筋腐蚀造成的钢筋混凝土（RC）结构耐久性能退化问题进行了评述,提出了需要进一步研究的问题.     

贵州不同油分烟叶化学成分的差异

分析贵州省烟区8个县烤烟主栽品种K326不同油分烟叶中的烟碱、总糖等主要化学成分的含量及其协调性。结果表明,多油分烟叶比少油分烟叶的烟碱、总氮和蛋白质含量低,总糖和还原糖含量高,施木克值高,糖碱比较协调;氯离子含量较低,钾氯比较高,多油分烟叶具有更优的物质基础。     

防火涂料对高强混凝土高温后氯离子渗透性影响

通过5组外包不同厚度防火涂料的C80高强混凝土试块的高温后氯离子渗透试验,研究了氯离子渗透性随涂料厚度的变化情况.试验结果表明：当防火涂料厚度≥30 mm时,高温后氯离子渗透性基本不变;当防火涂料厚度为20～25 mm时,高温后氯离子渗透性低于常温C50混凝土;当防火涂料厚度为15 mm时,高温后氯离子渗透性相对较高.综合考虑后认为,厚度20 mm的防火涂料可同时发挥抑制高强混凝土高温爆裂和降低高温后高强混凝土氯离子渗透性的双重作用.     

Isopycnic separation of subcellular components from poliovirus-infected and normal HeLa cells

A rapid method for determining the density of ribonucleoprotein particles and complexes has been developed. The method involves glutaraldehyde fixation of sucrose gradient fractions and immediate centrifugation for 5 hours through preformed cesium chloride gradients. There is little or no aggregation of particles, so that components which co-sediment in sucrose gradients are resolved by the cesium chloride gradient. By this method the densities of HeLa cell ribosomes, polyribosomes, and subribosomal particles have been determined. Furthermore, the poliovirus replication complex has been separated from polyribosomes and its density has been found to be unaffected by treatment with ethylene-diaminetetraacetic acid.     

植物液泡膜H+-ATPase和H+-PPase研究进展

植物液泡膜 ATP 酶（H+-ATPase）和液泡膜焦磷酸酶（H+-PPase）是液泡膜上两个含量丰富的蛋白,其功能的正常发挥在植物生长发育过程中扮演着重要角色。液泡膜 H+-ATPase 和 H+-PPase 水解底物释放能量,同时产生大量 H+由胞质泵入液泡内,形成细胞质与液泡间的 H+ 电化学势梯度,为多种溶质分子的跨膜主动运输提供驱动力,维持细胞内的离子稳态和渗透平衡,为细胞内各种生理生化反应的正常运行提供保障。此外,液泡作为植物细胞离子养分的储存库,其膜上 H+-ATPase 和 H+-PPase 能够通过改变其活性来调控硝酸盐在胞质和液泡间的分配比例,进而影响植物的氮素利用效率。在逆境胁迫条件下,提高液泡膜 H+-ATPase 和 H+-PPase 的活性有利于提高植株对逆境的适应能力,从而减少逆境胁迫对植株生长发育造成的不利影响。介绍了植物液泡膜 H+-ATPase 和 H+-PPase 的结构特征及其在植物生长发育过程中的生理功能,并对其在植物抵御非生物逆境胁迫过程中发挥的重要作用进行阐述,为进一步提高作物的氮素利用率及逆境适应能力提供方向。     

一维梯度铁纳米线的制备与表征

用氧化铝模板法和电化学沉积法控制合成了一维梯度直径铁纳米线.通过匀速减小氧化铝模板二次氧化的氧化电压,获得了具有一维梯度孔径的氧化铝模板,在此模板中利用电化学沉积法生长了具有一维梯度直径的铁纳米线.用扫描电镜和透射电镜对梯度直径铁纳米线进行表征,结果显示:铁纳米线呈细长锥形结构;沿长度方向,铁纳米线的直径具有梯直径变化,直径变化范围为12~31 nm.     

Molecular basis of gating charge immobilization in Shaker potassium channels

Voltage-dependent ion channels respond to changes in the membrane potential by means of charged voltage sensors intrinsic to the channel protein. Changes in transmembrane potential cause movement of these charged residues, which results in conformational changes in the channel. Movements of the charged sensors can be detected as currents known as gating currents. Measurement of the gating currents of the Drosophila Shaker potassium channel indicates that the charge on the voltage sensor of the channels is progressively immobilized by prolonged depolarizations. The charge is not immobilized in a mutant of the channel that lacks inactivation. These results show that the region of the molecule responsible for inactivation interacts, directly or indirectly, with the voltage sensor to prevent the return of the charge to its original position. The gating transitions between closed states of the channel appear not to be independent, suggesting that the channel subunits interact during activation.     

锂离子电池锡镍合金负极材料的性能研究

采用基于密度泛函理论的第一性原理平面波赝势方法计算了Sn-Ni合金中2种稳定相结构的物理性质和电化学性质.结果表明:Ni3Sn2具有相对稳定的电化学电位,Ni3Sn4具有波动性电化学电位.同时运用电化学沉积制备了Sn-Ni合金负极材料,测试结果标明Ni3Sn4具有优异的电化学性能,是适合用作锂离子电池的理想结构材料.     

Control of the selectivity of the aquaporin water channel family by global orientational tuning

Aquaporins are transmembrane channels found in cell membranes of all life forms. We examine their apparently paradoxical property, facilitation of efficient permeation of water while excluding protons, which is of critical importance to preserving the electrochemical potential across the cell membrane. We have determined the structure of the Escherichia coli aquaglyceroporin GlpF with bound water, in native (2.7 angstroms) and in W48F/F200T mutant (2.1 angstroms) forms, and carried out 12-nanosecond molecular dynamics simulations that define the spatial and temporal probability distribution and orientation of a single file of seven to nine water molecules inside the channel. Two conserved asparagines force a central water molecule to serve strictly as a hydrogen bond donor to its neighboring water molecules. Assisted by the electrostatic potential generated by two half-membrane spanning loops, this dictates opposite orientations of water molecules in the two halves of the channel, and thus prevents the formation of a "proton wire," while permitting rapid water diffusion. Both simulations and observations revealed a more regular distribution of channel water and an increased water permeability for the W48F/F200T mutant.     

黄牛FSHR基因的生物信息学分析

利用生物基因组学数据库,对黄牛FSHR基因进行生物信息学分析,以预测FSHR基因编码产物的理化性质、结构与功能,同时构建FSHR同源系统进化树.结果表明:FSHR基因编码产物为疏水性跨膜蛋白,具有明显的信号肽,其切割位点位于17～18位的氨基酸之间,二级结构主要以α-螺旋与无规则卷曲为主,并主要在质膜中发挥生物学作用,跨膜区域分为跨膜域、胞外域和胞内域3个部分.序列分析表明,FSHR编码产物可能具有离子通道、运载体、受体、信号转导和阳离子通道等功能,在离子跨膜与信号传递过程中发挥重要作用,并对黄牛的激素调节有影响.FSHR基因编码产物系统进化树表明,黄牛FSHR与水牛、成都麻羊、绵羊等物种FSHR遗传距离较近,具有高度同源性.     

Acetylcholine receptor: an allosteric protein

The nicotine receptor for the neurotransmitter acetylcholine is an allosteric protein composed of four different subunits assembled in a transmembrane pentamer alpha 2 beta gamma delta. The protein carries two acetylcholine sites at the level of the alpha subunits and contains the ion channel. The complete sequence of the four subunits is known. The membrane-bound protein undergoes conformational transitions that regulate the opening of the ion channel and are affected by various categories of pharmacologically active ligands.     

Mutations affecting internal TEA blockade identify the probable pore-forming region of a K+ channel

The active site of voltage-activated potassium channels is a transmembrane aqueous pore that permits ions to permeate the cell membrane in a rapid yet highly selective manner. A useful probe for the pore of potassium-selective channels is the organic ion tetraethylammonium (TEA), which binds with millimolar affinity to the intracellular opening of the pore and blocks potassium current. In the potassium channel encoded by the Drosophila Shaker gene, an amino acid residue that specifically affects the affinity for intracellular TEA has now been identified by site-directed mutagenesis. This residue is in the middle of a conserved stretch of 18 amino acids that separates two locations that are both near the external opening of the pore. These findings suggest that this conserved region is intimately involved in the formation of the ion conduction pore of voltage-activated potassium channels. Further, a stretch of only eight amino acid residues must traverse 80 percent of the transmembrane electric potential difference.     

运城盐湖卤水化学需氧量的测定

[目的]探索氯耗氧曲线校正法测定盐湖卤水中的COD值的效果。[方法]用氯耗氧曲线校正法测定运城市盐湖卤水的化学需氧量,并与其他的一些化学分析方法进行比较。[结果]在测定条件下,氯离子极易被重铬酸钾氧化,氯离子完全氧化时间为30min。CODCr（C1）与氯离子浓度之间有较好的线性关系,线性回归方程为Y=0．2224x-0．519,相关系数r=0．9876。通过测定得知,水样中氯离子的浓度为3503．85mg／L,通过耗氧曲线及方程得出运城市盐湖卤水中的CODCr的值为438．18mg／L,显示其污染较严重,需要进一步保护。[结论]用氯耗氧曲线校正法测定盐湖卤水COD值操作简单、简便、准确度高、精密性好,同时还可避免汞盐污染环境。     

The structure of an open form of an E. coli mechanosensitive channel at 3.45 A resolution

How ion channels are gated to regulate ion flux in and out of cells is the subject of intense interest. The Escherichia coli mechanosensitive channel, MscS, opens to allow rapid ion efflux, relieving the turgor pressure that would otherwise destroy the cell. We present a 3.45 angstrom-resolution structure for the MscS channel in an open conformation. This structure has a pore diameter of approximately 13 angstroms created by substantial rotational rearrangement of the three transmembrane helices. The structure suggests a molecular mechanism that underlies MscS gating and its decay of conductivity during prolonged activation. Support for this mechanism is provided by single-channel analysis of mutants with altered gating characteristics.