Structural basis of multiple drug-binding capacity of the AcrB multidrug efflux pump

Multidrug efflux pumps cause serious problems in cancer chemotherapy and treatment of bacterial infections. Yet high-resolution structures of ligand transporter complexes have previously been unavailable. We obtained x-ray crystallographic structures of the trimeric AcrB pump from Escherichia coli with four structurally diverse ligands. The structures show that three molecules of ligands bind simultaneously to the extremely large central cavity of 5000 cubic angstroms, primarily by hydrophobic, aromatic stacking and van der Waals interactions. Each ligand uses a slightly different subset of AcrB residues for binding. The bound ligand molecules often interact with each other, stabilizing the binding.     

杜仲ABC转运蛋白基因家族成员鉴定与分析

ABC转运蛋白(ATP—binding cassette transpoter)是一类庞大而古老的跨膜运输蛋白家族,在生物体内参与多种物质的转运积累、有害物质解毒、气孔调节、植物防御等生理活动。杜仲(Eucommia ulmoides Oliv)作为重要的中药材,其药用成分主要为次生代谢产物,次生代谢物转运与积累过程需要ABC转运蛋白的参与。利用生物信息学手段对杜仲ABC转运蛋白基因家族进行鉴定,并分析该家族蛋白质性质和结构、跨膜结构、亚细胞定位、系统进化关系。研究表明,EuABC家族生物信息学预测有76个成员,含有1~7个保守基序;编码蛋白多为稳定蛋白,主要分布于细胞质膜上,二级结构以α-螺旋和无规卷曲为主要构成元件;进化树分析表明,杜仲ABC转运蛋白家族可分为8个亚家族(A~G;I),每组成员数量分别为3、19、14、1、1、1、29、8。研究结果可为进一步研究杜仲次生代谢物质转运与积累奠定基础,也为其他植物ABC转运蛋白家族的研究提供了参考依据。     

Structure of Nup58/45 suggests flexible nuclear pore diameter by intermolecular sliding

The nucleoporins Nup58 and Nup45 are part of the central transport channel of the nuclear pore complex, which is thought to have a flexible diameter. In the crystal structure of an alpha-helical region of mammalian Nup58/45, we identified distinct tetramers, each consisting of two antiparallel hairpin dimers. The intradimeric interface is hydrophobic, whereas dimer-dimer association occurs through large hydrophilic residues. These residues are laterally displaced in various tetramer conformations, which suggests an intermolecular sliding by 11 angstroms. We propose that circumferential sliding plays a role in adjusting the diameter of the central transport channel.     

亚热带植物水力性状与木质部解剖结构的关系

【目的】植物水力系统需要对不断变化的水分环境做出适应性调整,因此,量化植物水力性状与木质部解剖结构在不同水分状况下的关系,将有助于理解植物的适应策略。【方法】以亚热带7种裸子植物和7种被子植物为研究材料,对比分析不同生境中(自然生境和人工生境)植物的栓塞抗性(植物导水率损失50%的水势)、输水效率和解剖结构的性状差异,探究植物水力性状与木质部解剖结构的关系。【结果】(1)在不同生境下,自然生境植物的输水效率(K_s)较大,栓塞抗性(P₅₀)较小,且植物解剖结构性状对不同生境植物水力性状具有一定指示性。(2)相关性分析表明：被子植物的导管水力直径、导管密度与K_s、P₅₀呈显著相关(P<0.05),但相关性在不同生境下呈相反趋势;裸子植物的管胞水力直径、管胞密度与K_s、P₅₀之间的相关性在不同生境中具有相同趋势。【结论】在湿润区内,植物通过增加输水效率以适应相对干旱环境的生存策略可能较为普遍。木质部结构与功能的差异可能是同一生境下植物水分策略存在差异的原因...     

Aligned multiwalled carbon nanotube membranes

An array of aligned carbon nanotubes (CNTs) was incorporated across a polymer film to form a well-ordered nanoporous membrane structure. This membrane structure was confirmed by electron microscopy, anisotropic electrical conductivity, gas flow, and ionic transport studies. The measured nitrogen permeance was consistent with the flux calculated by Knudsen diffusion through nanometer-scale tubes of the observed microstructure. Data on Ru(NH3)6(3+) transport across the membrane in aqueous solution also indicated transport through aligned CNT cores of the observed microstructure. The lengths of the nanotubes within the polymer film were reduced by selective electrochemical oxidation, allowing for tunable pore lengths. Oxidative trimming processes resulted in carboxylate end groups that were readily functionalized at the entrance to each CNT inner core. Membranes with CNT tips that were functionalized with biotin showed a reduction in Ru(NH3)6(3+) flux by a factor of 15 when bound with streptavidin, thereby demonstrating the ability to gate molecular transport through CNT cores for potential applications in chemical separations and sensing.     

植物叶片中RuBP羧化酶／加氧酶及光反应机构衰老机理的研究进展

在作者及其实验室多年研究的基础上，针对今后的研究方向，对国内外在植物光合机构与功能衰老研究的进展进行综述和讨论。叶向导度、ＲｕｂｉｓＣＯ含量、ＲｕＢＰＣａｓｅ活性及光系统活性是老化过程中光合速率的内部限制因素。在衰老过程中，１，５－二磷酸核酮糖羧化酶／加氧酶活性降低，ＲｕｂｉｓＣＯ蛋白合成在转录和翻译水平上均受到抑制，同时ＲｕｂｉｓＣＯ蛋白也受到蛋白水解酶的分解；类囊体膜结构紊乱，膜上结合色素、脂类和功能蛋白受到破坏，光合电子传递链活性及光合磷酸化水平发生衰退。植物光合机构及功能衰老在多条途径上渐次展开，叶绿体内光合电子传递生成还原物质的过程与碳素、氮素同化及Ｍｅｌｈｅｒ反应利用还原物质过程之间的失衡可能是光合机构不可逆衰老的重要机制。     

农村运输机械耗油量数学模型的研究

燃油消耗是农村运输机械作业的主要消耗项目,通过对农村运输机械复杂的运输作业过程的分析,提出了农村运输机械年平均运程及其回程满载、空载的等效关系模型,进而推出了综合反映运输条件特性和运输机械结构条件参数的农村运输机械耗油量数学模型,并经实例试验计算证实了模型的适用性.     

运输胁迫对四指马鲅幼鱼肝脏、鳃和脾脏组织结构的影响

[目的]探究运输胁迫对四指马鲅(Eleutheronema tetradactylum)幼鱼肝脏、鳃、脾脏组织结构的影响,提高种苗运输存活率,为其规模化养殖提供技术支持.[方法]以四指马鲅幼鱼为研究对象,分别设对照组(未运输)、混合组(运输,同时添加抗应激混合物)和空白组(运输,不添加任何抗应激剂),抗应激剂为维生素C∶谷氨酰胺=1∶1.混合组和空白组幼鱼经6h运输后分别取样(肝脏、鳃和脾脏),经石蜡切片和HE染色,显微镜下观察测定肝脏、鳃和脾脏的细胞形态、组织结构、生活及生理状态.[结果]对照组幼鱼表现正常,未出现死亡现象,混合组幼鱼的累计死亡率为12.5%,空白组的累计死亡达27.5%.对照组幼鱼的各组织均呈正常形态;混合组幼鱼的肝脏部分区域细胞排列疏松,肝小板结构不清晰;空白组幼鱼的肝脏组织整体失去固有形态,肝小板结构消失不见,大部分细胞核变性呈椭圆形或纺锤形.混合组幼鱼的鳃丝排列混乱,少数鳃小片末端或整体肿胀,血窦内红细胞出现部分堆积现象,线粒体丰富细胞体积变大;空白组的鳃小片整体肿胀,血窦加粗,部分鳃小片因红细胞过多而胀破,线粒体丰富细胞体积变大且数量增多.混合组幼鱼的脾脏白髓区域相对增大,黑色素—巨噬细胞中心数量及大小均有所增加;空白组幼鱼的脾脏组织红髓区域占据大部分,白髓区域相对较少,呈零散分布,巨噬细胞中心减小.[结论]运输胁迫导致四指马鲅幼鱼肝脏、鳃及脾脏组织损伤,抗应激剂混合物虽然在一定程度上起到缓解作用,但并不能完全消除.     

The crystal structure of a sodium galactose transporter reveals mechanistic insights into Na+/sugar symport

Membrane transporters that use energy stored in sodium gradients to drive nutrients into cells constitute a major class of proteins. We report the crystal structure of a member of the solute sodium symporters (SSS), the Vibrio parahaemolyticus sodium/galactose symporter (vSGLT). The approximately 3.0 angstrom structure contains 14 transmembrane (TM) helices in an inward-facing conformation with a core structure of inverted repeats of 5 TM helices (TM2 to TM6 and TM7 to TM11). Galactose is bound in the center of the core, occluded from the outside solutions by hydrophobic residues. Surprisingly, the architecture of the core is similar to that of the leucine transporter (LeuT) from a different gene family. Modeling the outward-facing conformation based on the LeuT structure, in conjunction with biophysical data, provides insight into structural rearrangements for active transport.     

p-nitrophenyl phosphate hydrolysis and calcium ion transport in fragmented sarcoplasmic reticulum

The calcium ion pump of fragmented sarcoplasmic reticulum can be coupled to hydrolysis of p-nitrophenyl phosphate, in the absence of added adenosine triphosphate. Comparison of the activities obtained with the two substrates suggests an analogous mechanism of transport. Independent of the substrate, a 2 : 1 ratio between calcium ion transport and substrate hydrolysis is displayed by the system, and an identical amount of work is required for ion transport against a given gradient. A phosphate ester appears necessary for substrate utilization in the pump mechanism, whereas the structure of the substrate determines the rates of activity and the affinity of the system for calcium ion.     

基于《易经》太极互动平衡理论的城乡空间结构布局探析

《易经》太极是中国古代重要的哲学思想之一,在中国文化中它包含万象,可以运用于各种事物及其关系的分析.将"阴阳平衡"理论、"天人合一"思想,运用于城乡规划领域,分析城市与乡村空间关系、分析它们在交通联系、物质与能量交换等方面的需要等.针对目前我国城市化进程中出现的许多问题,均可以从易经太极的智慧中得到启发,提示我们在城市化发展过程中应该如何处理"城市"与"乡村"的关系.     

Fine structure constant defines visual transparency of graphene

There are few phenomena in condensed matter physics that are defined only by the fundamental constants and do not depend on material parameters. Examples are the resistivity quantum, h/e2 (h is Planck's constant and e the electron charge), that appears in a variety of transport experiments and the magnetic flux quantum, h/e, playing an important role in the physics of superconductivity. By and large, sophisticated facilities and special measurement conditions are required to observe any of these phenomena. We show that the opacity of suspended graphene is defined solely by the fine structure constant, a = e2/hc feminine 1/137 (where c is the speed of light), the parameter that describes coupling between light and relativistic electrons and that is traditionally associated with quantum electrodynamics rather than materials science. Despite being only one atom thick, graphene is found to absorb a significant (pa = 2.3%) fraction of incident white light, a consequence of graphene's unique electronic structure.     

带悬板排沙漏斗三维流场测试

本文首次利用激光多普勒测速仪（ＬＤＡ）测试了排沙漏斗的三维螺旋流流场，并对其时均流特性及紊动特性进行了分析。     

植物ABC转运蛋白功能研究进展

植物ABC转运蛋白家族通过转运各种底物而参与植物一系列生命活动,其拥有众多家族成员,分类众多、结构复杂、功能多样。本文详细梳理了植物ABC转运蛋白的结构、分类及功能后发现,植物类转运蛋白共有8大亚族(ABCA～ABCG和ABCI),其中ABCG属于功能最多的一类亚族,主要参与代谢产物和激素转运、器官形成和物质合成,在重金属/逆境胁迫、以及次级代谢产物分泌等方面发挥着重要作用;ABCB主要参与生长素及重金属转运,刺激细胞生长,加强非生物胁迫的耐受能力;ABCC除参与次生代谢产物的转运外,还具有重金属解毒功能;ABCA类很可能与动植物的脂质代谢关系密切。对于目前功能未知的其他亚族建议开展蛋白互作研究,注重实践应用及多学科联合,更加准确具体解析其功能。全面深入研究植物ABC转运蛋白家族将为其他类转运蛋白的研究提供借鉴方法,同时为植物源/库的高效调控提供基础理论。     

不同结构草皮缓冲带对农田径流氮磷去除效果研究

通过对流过不同结构型式混播草皮缓冲带径流中污染物迁移影响的分析,研究其对农田径流氮磷的去除效果。结果表明,在TN、TP进水平均浓度分别为17.89 mg/L和1.04 mg/L的试验条件下,混播草皮缓冲带结构对农田径流TN、TP的去除能力具有明显差异,含有生态草沟的混播草皮缓冲带对TN、TP的去除能力明显强于单一缓坡和缓坡-阶梯结构的混播草皮缓冲带,其对径流水TN和渗流水TN的质量浓度削减率分别为51.08%和58.75%,对径流水TP和渗流水TP的质量浓度削减率分别为51.31%和65.29%。     

Structure and function of lipopolysaccharide binding protein

The primary structure of lipopolysaccharide binding protein (LBP), a trace plasma protein that binds to the lipid A moiety of bacterial lipopolysaccharides (LPSs), was deduced by sequencing cloned complementary DNA. LBP shares sequence identity with another LPS binding protein found in granulocytes, bactericidal/permeability-increasing protein, and with cholesterol ester transport protein of the plasma. LBP may control the response to LPS under physiologic conditions by forming high-affinity complexes with LPS that bind to monocytes and macrophages, which then secrete tumor necrosis factor. The identification of this pathway for LPS-induced monocyte stimulation may aid in the development of treatments for diseases in which Gram-negative sepsis or endotoxemia are involved.     

风场及光伏电场配置对阵列风沙结构影响的模拟分析

以对比分析不同风场及电站配置模式下光伏阵列对风沙输移的影响差异为研究目的,通过风洞模拟实验对不同风速、风向、电站阵列行距及是否布设麦草沙障时阵列在0~50 cm内的输沙情况进行分析,并对风沙流结构进行了探讨。结果表明:1)在0~50 cm高度范围内,阵列模型的输沙率与风速大小呈正比,与集沙高度呈反比,3个试验风速下输沙率均以多项式拟合关系最佳;2)当风向为南风时阵列输沙率及其风沙流结构特征值(λ)最高,南风(180°)、东北风(45°)、西北风(315°)的输沙最佳拟合函数分别为多项式函数、对数函数和指数函数;3)当阵列行距为20 cm时(以野外电场为原型等比例缩小值)阵列输沙率最高;4)当阵列前端布设麦草沙障后阵列风沙流结构特征值(λ)为1.75,即此时风沙流呈不饱和状态,具有挟沙能力。      

植物钾(K~+)离子通道的研究

钾在植物生长发育过程中具有许多重要的作用,钾离子通道是植物吸收钾离子的重要途径之一,根据结构和功能的不同钾离子通道可分为Shaker家族通道、KCO通道、其他通道。对上述植物钾离子通道蛋白的生化特性以及结构功能及相关基因研究的进展进行了详细的综述。     

鹫峰国家森林公园土壤溶质运移特征研究

溶质在土壤中的运移受土壤结构、质地、水分含量、地被植物等因素的影响。在室内条件下,采用恒定水头法研究亮蓝在鹫峰地区土壤中的运移规律,得到同一样地不同深度下的亮蓝穿透曲线。研究结果表明:在鹫峰地区,溶质在土壤中存在明显的优先运移现象,土壤容重、孔隙度和饱和导水率均能影响溶质在土壤中的运移。     

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.