Structure of a glycerol-conducting channel and the basis for its selectivity

Membrane channel proteins of the aquaporin family are highly selective for permeation of specific small molecules, with absolute exclusion of ions and charged solutes and without dissipation of the electrochemical potential across the cell membrane. We report the crystal structure of the Escherichia coli glycerol facilitator (GlpF) with its primary permeant substrate glycerol at 2.2 angstrom resolution. Glycerol molecules line up in an amphipathic channel in single file. In the narrow selectivity filter of the channel the glycerol alkyl backbone is wedged against a hydrophobic corner, and successive hydroxyl groups form hydrogen bonds with a pair of acceptor, and donor atoms. Two conserved aspartic acid-proline-alanine motifs form a key interface between two gene-duplicated segments that each encode three-and-one-half membrane-spanning helices around the channel. This structure elucidates the mechanism of selective permeability for linear carbohydrates and suggests how ions and water are excluded.     

Ion selectivity in a semisynthetic K+ channel locked in the conductive conformation

Potassium channels are K+-selective protein pores in cell membrane. The selectivity filter is the functional unit that allows K+ channels to distinguish potassium (K+) and sodium (Na+) ions. The filter's structure depends on whether K+ or Na+ ions are bound inside it. We synthesized a K+ channel containing the d-enantiomer of alanine in place of a conserved glycine and found by x-ray crystallography that its filter maintains the K+ (conductive) structure in the presence of Na+ and very low concentrations of K+. This channel conducts Na+ in the absence of K+ but not in the presence of K+. These findings demonstrate that the ability of the channel to adapt its structure differently to K+ and Na+ is a fundamental aspect of ion selectivity, as is the ability of multiple K+ ions to compete effectively with Na+ for the conductive filter.     

小麦水通道蛋白基因家族的全基因组鉴定及其在盐和干旱胁迫响应中的作用

水通道蛋白(AQPs)的功能是选择性地控制水和其他小分子通过细胞膜的流动,它们在植物的许多生理过程中都是至关重要的,包括非生物胁迫反应.小麦(Triticum aestivum L.)是全球重要的粮食作物,但干旱和盐胁迫是小麦生长和产量形成的重要影响因素.共鉴定得到了 127个非冗余的小麦水通道蛋白基因和4个可变剪接体.对TaAQP基因进行了 RNA-seq分析,揭示了小麦AQP基因的特异性表达模式.其中,TaTIPs和TaPIPs的表达高于TaNIPs和TaSIPs.qRT-PCR分析表明,小麦在干旱和盐胁迫条件下,TaNIP4;03_3D,TaTIP2;02b_7B,TaSIP2;02_4A,TaNIP3;03_6D 和 TaNIP2;04a_7D 等 AQPs 受到显著诱导并且有高表达量,表明它们参与了胁迫响应.这些结果为进一步探索TaAQPs基因在植物应对干旱胁迫和盐胁迫中的作用提供了新的思路.     

饥饿时间对大型溞摄食行为的影响

研究了不同饥饿时间下大型溞Daphnia magna(体长约3 mm)对沙角衣藻Chlamydomonas sajao和蛋白核小球藻Chlorella pyrenoidos的摄食选择性。沙角衣藻与蛋白核小球藻相比,具有较高的适口性,但营养价值相对较低。按照沙角衣藻和蛋白核小球藻的比例分别为5×104∶35×104、20×104∶20×104、35×104∶5×104cells/m L混合投喂饥饿0、0.25、1、4、8 d的大型溞,3 h后测定大型溞的摄食率、滤水率和食物选择系数。结果表明:与饱食组和短时间饥饿(0.25、1 d)组相比,长时间饥饿(4、8 d)导致大型溞对蛋白核小球藻的摄食率和滤水率显著增加(P<0.05),而对沙角衣藻的摄食率和滤水率显著降低(P<0.05);饱食和短时间饥饿状态下大型溞优先摄食沙角衣藻,而在长时间饥饿状态下大型溞优先摄食蛋白核小球藻;大型溞在长时间饥饿和短时间饥饿状态(含饱食)下的最优觅食行为不受食物中沙角衣藻与蛋白核小球藻相对密度的影响。研究表明,大型溞的饥饿状态可以影响其对藻类食物的选择性。     

饥饿时间对大型溞摄食行为的影响

研究了不同饥饿时间下大型溞Daphnia magna (体长约3 mm)对沙角衣藻Chlamydomonas sajao和蛋白核小球藻Chlorella pyrenoidos的摄食选择性。沙角衣藻与蛋白核小球藻相比,具有较高的适口性,但营养价值相对较低。按照沙角衣藻和蛋白核小球藻的比例分别为5×104.35×104、20×104.20×104、35×104.5×104 cells/mL混合投喂饥饿0、0·25、1、4、8 d的大型溞,3 h后测定大型溞的摄食率、滤水率和食物选择系数。结果表明：与饱食组和短时间饥饿(0·25、1 d)组相比,长时间饥饿(4、8 d)导致大型溞对蛋白核小球藻的摄食率和滤水率显著增加(P<0·05),而对沙角衣藻的摄食率和滤水率显著降低(P<0·05);饱食和短时间饥饿状态下大型溞优先摄食沙角衣藻,而在长时间饥饿状态下大型溞优先摄食蛋白核小球藻;大型溞在长时间饥饿和短时间饥饿状态(含饱食)下的最优觅食行为不受食物中沙角衣藻与蛋白核小球藻相对密度的影响。研究表明,大型溞的饥饿状态可以影响其对藻类食物的选择性。     

Crystal structure of a mammalian voltage-dependent Shaker family K+ channel

Voltage-dependent potassium ion (K+) channels (Kv channels) conduct K+ ions across the cell membrane in response to changes in the membrane voltage, thereby regulating neuronal excitability by modulating the shape and frequency of action potentials. Here we report the crystal structure, at a resolution of 2.9 angstroms, of a mammalian Kv channel, Kv1.2, which is a member of the Shaker K+ channel family. This structure is in complex with an oxido-reductase beta subunit of the kind that can regulate mammalian Kv channels in their native cell environment. The activation gate of the pore is open. Large side portals communicate between the pore and the cytoplasm. Electrostatic properties of the side portals and positions of the T1 domain and beta subunit are consistent with electrophysiological studies of inactivation gating and with the possibility of K+ channel regulation by the beta subunit.     

长距离输水渠道衬砌型式比较分析

长距离输水渠道的地质条件复杂,其衬砌型式是影响渠道施工进度和投资的一个关键性问题。本文以哈达山水利枢纽工程输水总干渠为研究对象,结合工程当地的气候、地质特点,通过混凝土板块、石笼及铰链式模袋混凝土三种衬砌型式的比较,简要介绍了该工程渠道的衬砌型式的选取,对类似工程有一定的借鉴意义。     

Impact of artificial reservoir water impoundment on global sea level

By reconstructing the history of water impoundment in the world's artificial reservoirs, we show that a total of approximately 10,800 cubic kilometers of water has been impounded on land to date, reducing the magnitude of global sea level (GSL) rise by -30.0 millimeters, at an average rate of -0.55 millimeters per year during the past half century. This demands a considerably larger contribution to GSL rise from other (natural and anthropogenic) causes than otherwise required. The reconstructed GSL history, accounting for the impact of reservoirs by adding back the impounded water volume, shows an essentially constant rate of rise at +2.46 millimeters per year over at least the past 80 years. This value is contrary to the conventional view of apparently variable GSL rise, which is based on face values of observation.     

A family of three mouse potassium channel genes with intronless coding regions

To understand the molecular mechanisms responsible for generating physiologically diverse potassium channels in mammalian cells, mouse genomic clones have been isolated with a potassium channel complementary DNA, MBK1, that is homologous to the Drosophila potassium channel gene, Shaker. A family of three closely related potassium channel genes (MK1, MK2, and MK3) that are encoded at distinct genomic loci has been isolated. Sequence analysis reveals that the coding region of each of these three genes exists as a single uninterrupted exon in the mouse genome. This organization precludes the generation of multiple forms of the protein by alternative RNA splicing, a mechanism known to characterize the Drosophila potassium channel genes Shaker and Shab. Thus, mammals may use a different strategy for generating diverse K+ channels by encoding related genes at multiple distinct genomic loci, each of which produces only a single protein.     

稻水象甲幼虫防治适期研究

对稻水象甲幼虫防治适期进行了试验研究,结果表明,在稻水象甲成虫高峰后3~8 d喷施对口药剂,能有效控制稻水象甲为害。     

Increased transport of antarctic bottom water in the vema channel during the last ice age

Particle size analyses of surface sediments in the Vema Channel reveal a spatial variation related to the present hydrography. Similar analyses of sediment deposited during the last ice age (18,000 years before the present) indicate a maximum shallowing of the upper limit of Antarctic Bottom Water (AABW) of about 100 meters, coupled with an increase in velocity, which resulted in an increase in AABW transport.     

Dendritic computation of direction selectivity by retinal ganglion cells

Direction-selective ganglion cells (DSGCs) in the retina respond strongly when stimulated by image motion in a preferred direction but are only weakly excited by image motion in the opposite null direction. Such coding represents an early manifestation of complex information processing in the visual system, but the cellular locus and the synaptic mechanisms have yet to be elucidated. We recorded the synaptic activity of DSGCs using strategies to observe the asymmetric inhibitory inputs that underlie the generation of direction selectivity. The critical nonlinear interactions between the excitatory and inhibitory inputs took place postsynaptically within the dendrites of the DSGCs.     

大棚反季蔬菜深沟养水栽培技术

1大棚反季蔬菜深沟养水技术原理和意义 1．1大棚反季蔬菜深沟养水技术原理 在温热地区大棚秋延后、冬早蔬菜生产的栽培管理中,有以下3组矛盾对蔬菜产量和品质的影响较大。     

西瓜主要病虫害的防治

为了提高西瓜的产量和经济效益,防治病虫为害是一个关键环节,下面我们就谈谈西瓜主要病虫害的防治。1枯萎病西瓜的枯萎病又叫“萎蔫病”、“蔓割病”,是西瓜的一种毁灭性病害。在整个西瓜生育过程中都能发病,尤以结瓜初期最盛。发病危害时     

几种化学除草剂对凤眼莲的防效研究

采用5种不同的化学除草剂,设6个组合对凤眼莲进行防治.结果表明:7.5%草灭星100 g/667m2 细土25kg/667 m2、18.2%田草净220 g/667 m2 细土25 kg/667 m2均匀撒施对凤眼莲有较好的防效,且速效性与持效性也较高,18.2%田草净11g 10%苄磺隆5 g 细土2.5 kg/66.7 m2的防效次之,20%使它隆100g/667m2对凤眼莲也有一定的防效.且所选用的除草剂对鱼虾类水生生物均无毒害作用.     

Graded regulation of the Kv2.1 potassium channel by variable phosphorylation

Dynamic modulation of ion channels by phosphorylation underlies neuronal plasticity. The Kv2.1 potassium channel is highly phosphorylated in resting mammalian neurons. Activity-dependent Kv2.1 dephosphorylation by calcineurin induces graded hyperpolarizing shifts in voltage-dependent activation, causing suppression of neuronal excitability. Mass spectrometry-SILAC (stable isotope labeling with amino acids in cell culture) identified 16 Kv2.1 phosphorylation sites, of which 7 were dephosphorylated by calcineurin. Mutation of individual calcineurin-regulated sites to alanine produced incremental shifts mimicking dephosphorylation, whereas mutation to aspartate yielded equivalent resistance to calcineurin. Mutations at multiple sites were additive, showing that variable phosphorylation of Kv2.1 at a large number of sites allows graded activity-dependent regulation of channel gating and neuronal firing properties.     

汉武帝与南部通道的开发

汉朝为了开通可以绕过匈奴与其他国家交往的道路,曾借用武力对西南夷进行了长达20年的开辟,并积极开发环北部湾港口。无论是西南夷道路的开辟还是北部湾港口的发展,都与汉武帝息息相关。     

Evaluation of reliability of water delivery by water supply systems

Simulation modeling methods are used to examine the problem of changing the normal functioning regimes of the system, failures, and restoration of its elements. The total time of failures during the period of operation and the contribution of individual elements to them are evaluated. Calculation is the basis of the new optimization methods.