Conformational changes associated with ion permeation in L-type calcium channels

The mechanism by which ions deliver their message to effector proteins involves a change in the protein conformation which is induced by the specific interaction of the ion with its binding site on the protein. In the case of an ion-channel protein, conformational changes induced by permeant ions and the consequences for channel function have received little attention. Here we report that binding of permeant cations to an intra-channel binding site of the dihydropyridine (DHP)-sensitive (L-type) Ca2+ channel leads to a conformational change which destabilizes the protonated state of a group on the external channel surface, and can shift its apparent pK value by more than 2 pH units. The lifetime of the protonated state correlates with the occupancy of an intra-channel binding site by the permeant cation. The demonstration of such conformational changes in a channel protein induced by the permeant ion has important implications for realistic models of the mechanism of ion permeation.     

The structural basis of calcium transport by the calcium pump

The sarcoplasmic reticulum Ca2+-ATPase, a P-type ATPase, has a critical role in muscle function and metabolism. Here we present functional studies and three new crystal structures of the rabbit skeletal muscle Ca2+-ATPase, representing the phosphoenzyme intermediates associated with Ca2+ binding, Ca2+ translocation and dephosphorylation, that are based on complexes with a functional ATP analogue, beryllium fluoride and aluminium fluoride, respectively. The structures complete the cycle of nucleotide binding and cation transport of Ca2+-ATPase. Phosphorylation of the enzyme triggers the onset of a conformational change that leads to the opening of a luminal exit pathway defined by the transmembrane segments M1 through M6, which represent the canonical membrane domain of P-type pumps. Ca2+ release is promoted by translocation of the M4 helix, exposing Glu 309, Glu 771 and Asn 796 to the lumen. The mechanism explains how P-type ATPases are able to form the steep electrochemical gradients required for key functions in eukaryotic cells.     

A 'snowball Earth' climate triggered by continental break-up through changes in runoff

Geological and palaeomagnetic studies indicate that ice sheets may have reached the Equator at the end of the Proterozoic eon, 800 to 550 million years ago, leading to the suggestion of a fully ice-covered 'snowball Earth'. Climate model simulations indicate that such a snowball state for the Earth depends on anomalously low atmospheric carbon dioxide concentrations, in addition to the Sun being 6 per cent fainter than it is today. However, the mechanisms producing such low carbon dioxide concentrations remain controversial. Here we assess the effect of the palaeogeographic changes preceding the Sturtian glacial period, 750 million years ago, on the long-term evolution of atmospheric carbon dioxide levels using the coupled climate-geochemical model GEOCLIM. In our simulation, the continental break-up of Rodinia leads to an increase in runoff and hence consumption of carbon dioxide through continental weathering that decreases atmospheric carbon dioxide concentrations by 1,320 p.p.m. This indicates that tectonic changes could have triggered a progressive transition from a 'greenhouse' to an 'icehouse' climate during the Neoproterozoic era. When we combine these results with the concomitant weathering effect of the voluminous basaltic traps erupted throughout the break-up of Rodinia, our simulation results in a snowball glaciation.     

基于CUSUM方法的中国股市波动变结构检验

利用CUSUM方法对中国沪深股票市场的波动变结构现象进行了研究.实证结果表明:1)上证综指和深证综指都存在明显的波动变结构现象,并且二者的波动变结构具有一致性和相关性;2)上证综指和深证综指在全样本区间都存在异方差效应且具有显著的波动聚集性,但在去除变结构效应后,二者均没有异方差效应.这表明变结构现象很可能是导致收益率序列产生异方差的原因.     

Mitochondrial response and calcium ion change in apoptotic insect cells induced by SfaMNPV

Mitochondrial responses and changes of calcium ions in apoptotic insect SL-1 cells induced by Syngrapha falcifera multiple nuclear polyhedrosis virus (SfaMNPV) are reported in this paper. By using Rhodamine 123 as a fluorescent labeling probe, flow cytometry analysis and confocal laser scanning microscope observation we observed that the mitochondrial transmembrane potential (△ψm) began to decrease in SL-1 cells at 4 h post infection and △ψm reduced continuously with the extension of virus infection. Western blotting indicated that the Bcl-2 level in the mitochondria gradually declined and was down- regulated. Cells undergoing apoptosis were found to have an elevation of cytochrome c in the cytosol and a corresponding decrease in the mitochondria, which indicated that cytochrome c was released from mitochondria into cytosol. These results suggest that mitochondrion-mediated apoptotic signal transduction pathway exists in apoptotic insect cell induced by SfaMNPV. Cytosolic free calcium ([Ca^2 ]i) concentration rapidly increased after SfaMNPV infection and the elevated calcium was tested to come partly from extracelllular calcium ion influx. Flow cytometry analysis indicated that the apoptosis in SL-1 cells was not influenced by established cytosolic calcium clamped conditions and the EGTA inhibiting calcium influx. Therefore, neither the elevation of cytosolic calcium ion nor extracellular calcium entry was the inducing factor of apoptosis, which hinted that the depletion of ER Ca^2 store contributed to SL-1 cell apoptosis induced by SfaMNPV.     

Synthesis of CuInS2 nanocrystals and their structural transformation triggered by ligand exchange

Chalcopyrite-type CulnS2 NCs was synthesized by the hot-soap method. Mixed solutions, Cul and InCl3 dissolved in the mixture of the tri-octylphosphite and 1-octadecene and the sulfur dissolved in tri-phenylphosphite, were used as source solutions; the hexadecylamine was additionally mixed as a surfactant before the reaction. It was observed that the product CulnS2 NCs structurally transformed from the chalcopyrite（CP）- or zincblende（ZB）- to the wurtzite（WZ）-type depending on the amount of the surfactant and a storage time after the surfactant addition. Very weak photoluminescence in the nearinfrared region was observed for the CP- or ZB-type NCs. This band was attributable to the electronhole recombination via defect levels. No photoluminescence was detected for the wurtzite-type NCs.     

Structural changes in the calcium pump accompanying the dissociation of calcium

In skeletal muscle, calcium ions are transported (pumped) against a concentration gradient from the cytoplasm into the sarcoplasmic reticulum, an intracellular organelle. This causes muscle cells to relax after cytosolic calcium increases during excitation. The Ca(2+) ATPase that carries out this pumping is a representative P-type ion-transporting ATPase. Here we describe the structure of this ion pump at 3.1 A resolution in a Ca(2+)-free (E2) state, and compare it with that determined previously for the Ca(2+)-bound (E1Ca(2+)) state. The structure of the enzyme stabilized by thapsigargin, a potent inhibitor, shows large conformation differences from that in E1Ca(2+). Three cytoplasmic domains gather to form a single headpiece, and six of the ten transmembrane helices exhibit large-scale rearrangements. These rearrangements ensure the release of calcium ions into the lumen of sarcoplasmic reticulum and, on the cytoplasmic side, create a pathway for entry of new calcium ions.     

金属及其合金中注入离子引发的基体长程效应

为研究金属及其合金基体中不同固溶度的注入离子引发的长程效应,采用固溶度相差较大的元素以及单晶和多晶为分析材料,用透射电子显微镜弱束成像技术研究了被注入材料的横截面样品.结果表明:铁、钨在单晶铜、多晶奥氏体不锈钢中固溶度很低,长程效应明显,在基体表层有位错密度峰值;注入离子剂量增加时,甚至出现两个位错密度峰值.钼和铁在奥氏体不锈钢中有较高的固溶度,注入离子在基体表层没有位错密度峰值出现.     

Core formation in planetesimals triggered by permeable flow

The tungsten isotope composition of meteorites indicates that core formation in planetesimals occurred within a few million years of Solar System formation. But core formation requires a mechanism for segregating metal, and the 'wetting' properties of molten iron alloy in an olivine-rich matrix is thought to preclude segregation by permeable flow unless the silicate itself is partially molten. Excess liquid metal over a percolation threshold, however, can potentially create permeability in a solid matrix, thereby permitting segregation. Here we report the percolation threshold for molten iron-sulphur compounds of approximately 5 vol.% in solid olivine, based on electrical conductivity measurements made in situ at high pressure and temperature. We conclude that heating within planetesimals by decay of short-lived radionuclides can increase temperature sufficiently above the iron-sulphur melting point (approximately 1,000 degrees C) to trigger segregation of iron alloy by permeable flow within the short timeframe indicated by tungsten isotopes. We infer that planetesimals with radii greater than about 30 km and larger planetary embryos are expected to have formed cores very early, and these objects would have contained much of the mass in the terrestrial region of the protoplanetary nebula. The Earth and other terrestrial planets are likely therefore to have formed by accretion of previously differentiated planetesimals, and Earth's core may accordingly be viewed as a blended composite of pre-formed cores.     

Energetic optimization of ion conduction rate by the K+ selectivity filter.

The K+ selectivity filter catalyses the dehydration, transfer and rehydration of a K+ ion in about ten nanoseconds. This physical process is central to the production of electrical signals in biology. Here we show how nearly diffusion-limited rates are achieved, by analysing ion conduction and the corresponding crystallographic ion distribution in the selectivity filter of the KcsA K+ channel. Measurements with K+ and its slightly larger analogue, Rb+, lead us to conclude that the selectivity filter usually contains two K+ ions separated by one water molecule. The two ions move in a concerted fashion between two configurations, K+-water-K+-water (1,3 configuration) and water-K+-water-K+ (2,4 configuration), until a third ion enters, displacing the ion on the opposite side of the queue. For K+, the energy difference between the 1,3 and 2,4 configurations is close to zero, the condition of maximum conduction rate. The energetic balance between these configurations is a clear example of evolutionary optimization of protein function.     

Detection of Structural Damage Through Changes in Frequency

0IntroductionThbeee nvi pbrroatpioosne-db aasnedd d deavemlaogpeed d iente tchtieo npa satp p3r0o aycehaerss , haanvdethe study onthis topicis still active[1].Since natural frequen-cies can provide the global information of structures ,and canbe exactly m…     

高钙粉煤灰陶粒对人工湿地强化除磷机制

为强化人工湿地除磷能力和扩大固体废弃物粉煤灰的利用,选择对磷吸附容量高的高钙粉煤灰陶粒作为人工湿地基质,考察除磷特性,探讨除磷机制.实验结果表明:高钙粉煤灰陶粒具有其巨大的比表面积和孔隙率,相对于传统基质具有较大的磷吸附容量,磷去除率可达90％,出水TP和PO43-质量浓度分别低于0.40 mg/L和0.22mg/L;粉煤灰陶粒吸附Ca-P达到总吸附磷量的90％,强化除磷的机制是陶粒内部的钙元素与水中的磷发生化学反应,造成磷在陶粒表面的沉积,进而达到从水中分离的目的,微生物分解和植物的进一步吸收能维持该过程的可持续性.     

Chemistry of ion coordination and hydration revealed by a K+ channel-Fab complex at 2.0 A resolution.

Ion transport proteins must remove an ion's hydration shell to coordinate the ion selectively on the basis of its size and charge. To discover how the K+ channel solves this fundamental aspect of ion conduction, we solved the structure of the KcsA K+ channel in complex with a monoclonal Fab antibody fragment at 2.0 A resolution. Here we show how the K+ channel displaces water molecules around an ion at its extracellular entryway, and how it holds a K+ ion in a square antiprism of water molecules in a cavity near its intracellular entryway. Carbonyl oxygen atoms within the selectivity filter form a very similar square antiprism around each K+ binding site, as if to mimic the waters of hydration. The selectivity filter changes its ion coordination structure in low K+ solutions. This structural change is crucial to the operation of the selectivity filter in the cellular context, where the K+ ion concentration near the selectivity filter varies in response to channel gating.     

生物技术在水产食品加工上之应用--利用生物技术生产鱼肉蛋白降解抑制剂

鲭鱼 (Scomberaustralasicus)、鳕鱼 (Merlucciusproductus)、鲑鱼 (Oncorhynchusketa)、大西洋产鳕鱼或比目鱼等鱼浆在冷冻贮藏过程中极易因CathepsinsB、H、I等之残存而造成品质下降 ,而且于制造鱼浆加工品时 ,常会在加热过程发生鱼浆解胶 (thermaldegradation)之品质劣变问题 .由过去之研究结果显示 ,CathepsinB、L等硫氢蛋白酶均会影响鱼浆蛋白的冷冻安定性及热凝胶特性 .由于从农、畜、水产原料中分离与制备蛋白酶抑制剂极不经济 ,且产量也受限 ,因此 ,本研究室将鸡肺的cystatincDNA序列利用pET - 2 3a(+)表现载体表现 ,并转送到大肠杆菌AD4 94 (DE3)pLysS细胞内 ,经由isopropyl- β -D -thiogalactopyranoside(IPTG)诱导 ,可在大肠杆菌细胞质内表现出高量具有正确蛋白分子内双硫键及活性之recombinantcystatin .基于安全及工业上量产之考量 ,本研究室亦将此cystatin的cDNA序列 ,接到PGAPZαC表现载体上并将此载体转送入酵母菌PichiapastorisX - 33细胞中 ,令cystatincDNA整合到此酵母菌核内之染色体DNA上 ,经由此载体上之GAPpromoter的调控及α -factorprepros equence之引导可以于培养液中大量的表现出具有正确蛋白结构及活性之胞外分泌型recombinantcystatin .以上两蛋白质均经由分离纯化及生化     

构筑湿地厌氧氨氧化脱氮研究

针对构筑湿地废水脱氮效率较低的问题,论文对构筑湿地传统硝化工艺作了改进以考察厌氧氨氧化自养脱氮的可行性.采用改进的非饱和与饱和层结合的垂直流湿地及水平流湿地组合工艺,与传统的垂直流湿地硝化与水平流湿地反硝化的脱氮工艺对比研究;并采用分子生物学荧光免疫原位杂交(Fluorescent in situ hybridization,FISH)技术对厌氧氨氧化细菌进行鉴定分析.实验结果表明,厌氧氨氧化反应途径在构筑湿地中具有实现的可行性,脱氮效率高于传统工艺.