Ice growth in supercooled solutions of antifreeze glycoprotein

Inhibition of ice growth in supercooled solution by certain proteins is vital to the survival of many living organisms. Some fish, native to both subzero northern and southern waters, have special proteins or glycoproteins in their blood serum that inhibit ice formation. Whereas these proteins have only a very small effect on the melting temperature of ice, the temperature of these fish can fall to nearly 1 K below the melting point before ice crystals grow. This phenomenon is called freezing hysteresis, in contrast to the normal colligative effect of solutes that depresses the equilibrium temperature, around which small changes lead to crystal growth or melting depending on sign. Some insects also exhibit a serum freezing hysteresis. We report the effects of different degrees of supercooling on the habit and rates of growth of ice crystals from solutions of these antifreeze glycoproteins (AFGPs). We find that the crystallization rate is up to five times greater than that in pure water.     

抗冻糖蛋白(AFGP1-5)溶液中自由生长条件下冰晶生长激活能的计算

根据冰晶生长速率理论，计算了抗冻糖蛋白（ＡＦＧＰ１－５）溶液中自由生长条件下冰晶生长的激活能．这种定量计算对研究抗冻糖蛋白溶液中冰晶生长习性有重要意义．     

鱼抗冻多肽溶液中冰晶生长习性

分析了鱼抗冻多肽分子的结构特点和鱼抗冻多肽溶液中抗冻多肽分子（ＡＦ（Ｇ）Ｐ）与冰晶表面的相互作用机理．提出了鱼抗冻多肽溶液中的冰晶生长理论．合理地解释了冰晶生长的各向异性习性．并给出了周期性键链理论的一个定量形式．     

鱼抗冻糖蛋白AFGP7－8的热滞研究

分析了鱼抗冻糖蛋白（ＡＦＧＰ７－８）的结构特点及在溶液中的特性，计算了ＡＦＧＰ７－８溶液的热滞，理论结果与实验数据较好地符合．     

吸水性涂层在霜层生长初期的抑霜

研究吸水性涂层对霜层生长过程的影响,以寻求抑制结霜的有效方法.通过自行设计的试验设备对吸水性涂层表面上霜层生长特性进行试验研究,获取了不同时段霜层的显微图片,采用数字图像处理方法对其分析,与无涂层的铜表面进行对比.结果表明,吸水性涂层使得结霜时间推迟,霜层高度下降,冰晶体分布稀疏.此外霜层生长初期冰晶体的结构发生了变化,晶体呈倒立状,在某个时段内持续这种状态.对列固含率的分析表明,吸水性涂层的表面在初期有些位置冰晶体含量较高,但有些位置则接近于零,这样的霜层在生长初期甚至加强了热传递.最后通过对比不同表面霜层高度随时间的变化规律发现:吸水性涂层在初期抑霜效果最好,随着时间的推移其抑霜能力逐渐下降.     

第一类鱼抗冻蛋白分子对冰晶表面平衡结构的影响

根据冰晶生长理论,在一定的生长驱动力作用下,冰晶界面生长机制和动力学规律决定于冰晶界面的微观结构.从大分子溶液热力学性质出发,得到了结合抗冻蛋白后冰晶表面微观平衡结构的变化,并讨论了这种变化对冰晶生长形态的影响.结果显示抗冻蛋白造成冰晶表面微观平衡结构改变,是抗冻蛋白溶液中冰晶生长的形态与纯水中冰晶生长的形态有显著区别的原因之一.     

Presynaptic neurones may contribute a unique glycoprotein to the extracellular matrix at the synapse

As the extracellular matrix at the original site of a neuromuscular junction seems to play a major part in the specificity of synaptic regeneration, considerable attention has been paid to unique molecules localized to this region. Here we describe an extracellular matrix glycoprotein of the elasmobranch electric organ that is localized near the nerve endings. By immunological criteria, it is synthesized in the cell bodies, transported down the axons and is related to a glycoprotein in the synaptic vesicles of the neurones that innervate the electric organ. It is apparently specific for these neurones, as it cannot be detected elsewhere in the nervous system of the fish. Therefore, neurones seem to contribute unique extracellular matrix glycoproteins to the synaptic region. Synaptic vesicles could be involved in transporting these glycoproteins to or from the nerve terminal surface.     

鱼抗冻蛋白溶液的热滞与蛋白分子量的关系

分析了鱼抗冻糖蛋白的抗冻机理，根据冰晶生长理论和Ｆｌｏｒｙ的大分子溶液理论，导出了抗冻糖蛋白的热滞（熔点与冰晶生长点之差）与抗冻糖蛋白的分子量的关系，结果与实验数据较好地符合。     

改进法制备枯草杆菌膜囊及其电镜观察

使用改进膜囊制备法得到枯草杆菌膜囊.电镜观察表明,该膜囊是中空的,仅由质膜组成的囊状封闭结构,其中存在较大比例的内部膜囊,同时观察到多种膜囊形成的中间过程,据此提出了膜囊形成的两种机制.     

A new class of synthetic antibacterials acting on lipopolysaccharide biosynthesis

Although there is a need for antibacterial agents that act only on Gram-negative bacteria, there are at present few such compounds. The 2-deoxy analogue of beta-KDO (3-deoxy-beta-D-manno-2-octulopyranosonic acid) is a potent inhibitor of a key enzyme (CMP-KDO synthetase) in lipopolysaccharide biosynthesis of Gram-negative bacteria, but it fails to penetrate intact bacteria. Coupling an L-L-dipeptide to the 8-amino-2,8-dideoxy analogue of beta-KDO enabled it to be recognized and actively accumulated by certain peptide permeases of the cytoplasmic membrane. The dipeptide was hydrolysed in the cell and the inhibitor released. Subsequent inhibition of CMP-KDO synthetase led to the accumulation of large amounts of lipid A precursor and bacterial death. These compounds represent a new class of synthetic antimicrobials with a novel mechanism of action and considerable potential as chemotherapeutic agents.     

超声波影响初始霜晶生长的微观可视化研究

试验研究了超声波对平板表面结霜初始阶段霜晶生长的影响.对自然对流条件下施加20kHz频率的超声波和未施加超声波两种作用机制下平板表面结霜初始阶段冻结水珠的形态、分布以及水珠冻结后水珠表面霜晶的生长进行了微观可视化研究.对有无超声波作用的不同冷表面温度下水珠冻结粒径的大小以及水珠分布的疏密进行了对比分析.同时对有无超声波作用下水珠冻结后水珠表面霜晶的生长进行了对比观测.试验结果显示:施加超声波作用后,冻结水珠粒径显著减小,形态相对规整且接近圆形;分布相对规则且明显稀疏;水珠冻结后其表面霜晶几乎不生长.结果表明:超声波对结霜初期冻结水珠的形成以及水珠冻结后水珠表面霜晶的生长具有显著的抑制作用.     

Mimicry of ice structure by surface hydroxyls and water of a beta-helix antifreeze protein

Insect antifreeze proteins (AFP) are much more effective than fish AFPs at depressing solution freezing points by ice-growth inhibition. AFP from the beetle Tenebrio molitor is a small protein (8.4 kDa) composed of tandem 12-residue repeats (TCTxSxxCxxAx). Here we report its 1.4-A resolution crystal structure, showing that this repetitive sequence translates into an exceptionally regular beta-helix. Not only are the 12-amino-acid loops almost identical in the backbone, but also the conserved side chains are positioned in essentially identical orientations, making this AFP perhaps the most regular protein structure yet observed. The protein has almost no hydrophobic core but is stabilized by numerous disulphide and hydrogen bonds. On the conserved side of the protein, threonine-cysteine-threonine motifs are arrayed to form a flat beta-sheet, the putative ice-binding surface. The threonine side chains have exactly the same rotameric conformation and the spacing between OH groups is a near-perfect match to the ice lattice. Together with tightly bound co-planar external water, three ranks of oxygen atoms form a two-dimensional array, mimicking an ice section.     

Crystal structure of enteropathogenic Escherichia coli intimin-receptor complex

Intimin and its translocated intimin receptor (Tir) are bacterial proteins that mediate adhesion between mammalian cells and attaching and effacing (A/E) pathogens. Enteropathogenic Escherichia coli (EPEC) causes significant paediatric morbidity and mortality world-wide. A related A/E pathogen, enterohaemorrhagic E. coli (EHEC; O157:H7) is one of the most important food-borne pathogens in North America, Europe and Japan. A unique and essential feature of A/E bacterial pathogens is the formation of actin-rich pedestals beneath the intimately adherent bacteria and localized destruction of the intestinal brush border. The bacterial outer membrane adhesin, intimin, is necessary for the production of the A/E lesion and diarrhoea. The A/E bacteria translocate their own receptor for intimin, Tir, into the membrane of mammalian cells using the type III secretion system. The translocated Tir triggers additional host signalling events and actin nucleation, which are essential for lesion formation. Here we describe the the crystal structures of an EPEC intimin carboxy-terminal fragment alone and in complex with the EPEC Tir intimin-binding domain, giving insight into the molecular mechanisms of adhesion of A/E pathogens.     

地面湿度对雷暴云电过程影响

分析了南京地区2002～2011年(共10年)闪电和地面相对湿度的卫星观测资料,分析表明:闪电密度与相对湿度呈正相关。为了进一步研究相对湿度对雷暴云起电和放电的影响,采用二维雷暴云起、放电数值模式进行敏感性试验。结果表明:随着相对湿度的增大,云滴数目增多,上升风速增强;当相对湿度增加时,较大的上升气流和云水含量有助于产生更大尺寸的冰晶和霰粒子;较大的云滴、霰和冰晶通过非感应起电和感应起电机制促进电荷分离;当相对湿度从60%增加到90%时,总闪数增加,并且只有当相对湿度高达90%时,才能产生地闪。整体而言,相对湿度越大,对流活动更快更强,促进了雷暴云初始起电和放电。     

Perennial water ice identified in the south polar cap of Mars

The inventory of water and carbon dioxide reservoirs on Mars are important clues for understanding the geological, climatic and potentially exobiological evolution of the planet. From the early mapping observation of the permanent ice caps on the martian poles, the northern cap was believed to be mainly composed of water ice, whereas the southern cap was thought to be constituted of carbon dioxide ice. However, recent missions (NASA missions Mars Global Surveyor and Odyssey) have revealed surface structures, altimetry profiles, underlying buried hydrogen, and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide. Here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes, at a resolution of 2 km, during the local summer, when the extent of the polar ice is at its minimum. We observe that this south polar cap contains perennial water ice in extended areas: as a small admixture to carbon dioxide in the bright regions; associated with dust, without carbon dioxide, at the edges of this bright cap; and, unexpectedly, in large areas tens of kilometres away from the bright cap.     

低温环境下木材细胞中冰晶的形成和传播研究综述

活立木树干内部水分状态对其生理作用的发挥具有重要的影响。低温下,活立木内部水分状态的改变,导致其结构发生变化,这给基于声波技术的活立木材质无损检测带来了一些困难。笔者从宏观和微观角度,综述了树干和木质细胞中冰晶的形成、传播、分布和冰晶体含量的最新研究结果; 讨论了木材细胞内和细胞外水分的冻结模式和冻结行为; 介绍了时域反射技术、低温扫描电镜、差热分析、核磁共振等研究木材内部水冻结过程的方法并比较了各方法的特点。认为当前研究在技术手段、研究对象和深度上仍需进一步拓展,未来应重点以活立木树干及枝干为对象,利用多种手段加强原位检测,对冰晶形成原因、扩展过程及产生结果进行系统研究。通过对低温木材中冰晶的形成和传播机制的综合分析,可为后续开展低温活立木无损检测和树木抗寒性研究提供参考。     

Vesicular restriction of synaptobrevin suggests a role for calcium in membrane fusion

Release of neurotransmitter occurs when synaptic vesicles fuse with the plasma membrane. This neuronal exocytosis is triggered by calcium and requires three SNARE (soluble-N-ethylmaleimide-sensitive factor attachment protein receptors) proteins: synaptobrevin (also known as VAMP) on the synaptic vesicle, and syntaxin and SNAP-25 on the plasma membrane. Neuronal SNARE proteins form a parallel four-helix bundle that is thought to drive the fusion of opposing membranes. As formation of this SNARE complex in solution does not require calcium, it is not clear what function calcium has in triggering SNARE-mediated membrane fusion. We now demonstrate that whereas syntaxin and SNAP-25 in target membranes are freely available for SNARE complex formation, availability of synaptobrevin on synaptic vesicles is very limited. Calcium at micromolar concentrations triggers SNARE complex formation and fusion between synaptic vesicles and reconstituted target membranes. Although calcium does promote interaction of SNARE proteins between opposing membranes, it does not act by releasing synaptobrevin from synaptic vesicle restriction. Rather, our data suggest a mechanism in which calcium-triggered membrane apposition enables syntaxin and SNAP-25 to engage synaptobrevin, leading to membrane fusion.     

蛭弧菌对草鱼池水质及细菌类群的影响

研究了蛭弧菌对草鱼池水质及细菌类群的影响,结果表明:蛭弧菌对养殖环境的主要水化指标具有明显的改善作用,实验组的平均COD、NH3-N、硫化物值显著低于对照组(P＜0.05),实验组的DO显著高于对照组(P＜0.05),而实验组与对照组的pH值差异不显著(P＞0.05);池水细菌总数及致病菌的数量也随着蛭弧菌浓度的增加而发生几何级数减少.     

Membrane vesicles traffic signals and facilitate group activities in a prokaryote

Many bacteria use extracellular signals to communicate and coordinate social activities, a process referred to as quorum sensing. Many quorum signals have significant hydrophobic character, and how these signals are trafficked between bacteria within a population is not understood. Here we show that the opportunistic human pathogen Pseudomonas aeruginosa packages the signalling molecule 2-heptyl-3-hydroxy-4-quinolone (pseudomonas quinolone signal; PQS) into membrane vesicles that serve to traffic this molecule within a population. Removal of these vesicles from the bacterial population halts cell-cell communication and inhibits PQS-controlled group behaviour. We also show that PQS actively mediates its own packaging and the packaging of other antimicrobial quinolines produced by P. aeruginosa into vesicles. These findings illustrate that a prokaryote possesses a signal trafficking system with features common to those used by higher organisms and outlines a novel mechanism for delivery of a signal critical for coordinating group behaviour in P. aeruginosa.     

Structural analysis of the essential self-cleaving type III secretion proteins EscU and SpaS

During infection by Gram-negative pathogenic bacteria, the type III secretion system (T3SS) is assembled to allow for the direct transmission of bacterial virulence effectors into the host cell. The T3SS system is characterized by a series of prominent multi-component rings in the inner and outer bacterial membranes, as well as a translocation pore in the host cell membrane. These are all connected by a series of polymerized tubes that act as the direct conduit for the T3SS proteins to pass through to the host cell. During assembly of the T3SS, as well as the evolutionarily related flagellar apparatus, a post-translational cleavage event within the inner membrane proteins EscU/FlhB is required to promote a secretion-competent state. These proteins have long been proposed to act as a part of a molecular switch, which would regulate the appropriate chronological secretion of the various T3SS apparatus components during assembly and subsequently the transported virulence effectors. Here we show that a surface type II beta-turn in the Escherichia coli protein EscU undergoes auto-cleavage by a mechanism involving cyclization of a strictly conserved asparagine residue. Structural and in vivo analysis of point and deletion mutations illustrates the subtle conformational effects of auto-cleavage in modulating the molecular features of a highly conserved surface region of EscU, a potential point of interaction with other T3SS components at the inner membrane. In addition, this work provides new structural insight into the distinct conformational requirements for a large class of self-cleaving reactions involving asparagine cyclization.