Numerical simulation of coil-helix transition processes of gelatin

Gelatin is widely used in food, pharmaceutical, and photographic industries due to the coil-helix transition, whereas the structural inhomogeneity considerably affects its essential properties closely connecting with the industrial applications. The spatially structural inhomogeneity of the gelatin caused by the uneven and unstable temperature field is analyzed by the finite element method during the cooling-induced coil-helix transition process. The helix conversion and the crosslinking density as functions of time and spatial grid are calculated by the incremental method. A length distribution density function is introduced to describe the continuous length distributions of two kinds of triple helices.

Evaluation of Effects of Bivalent Cations on the Formation of Purine-rich Triple-Helix DNA by ESI-FT-MS

The GGA triplet repeats are widely dispersed throughout eukaryotic genomes. (GGA)n or (GGT)n oligonucleotides can interact with double-stranded DNA containing (GGA:CCT)n to form triple-stranded DNA. The effects of 8 divalent metal ions (3 alkaline-earth metals and 5 transition metals) on formation of these purine-rich triple-helix DNA were investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-MS). In the absence of metal ions, no triplex but single-strand, duplex, and purine homodimer ions were observed in mass spectra. The triple-helix DNA complexes were observed only in the presence of certain divalent ions. The effects of different divalent cations on the formation of purine-rich triplexes were compared. Transition-metal ions, especially Co2+ and Ni2+, significantly boost the formation of triple-helix DNA, whereas alkaline-earth metal ions have no positive effects on triplex formation. In addition, Ba2+ is notably beneficial to the formation of homodimer instead of triplex.

Helix-sense-selective polymerization of N,N-diphenyl (meth)acrylamide by anionic catalysts

In this paper, the helix-sense-selective polymerization of N,N-diphenyl acrylamide (DPAA) and N,N-diplienyl methacrylamide(DPMAA) were studied with living helix prepolymer as anionic initiator, and the chiral optical properties of the obtained polymers were investigated too. It was shown that optically active polymers of DPAA and DPMAA could be obtained under the experimental condition, and exhibited the same screw sense as that of the prepolymer.

Electric field-induced conformational transition of bovine serum albumin from alpha-helix to beta-sheet

The irreversible conformational transition of bovine serum albumin (BSA) from alpha-helix to beta-sheet, induced by electric field near the electrode surface, was monitored by circular dichroism (CD) with a long optical path thin layer cell (LOPTLC).

HELIX-INDUCED ASYMMETRIC POLYMERIZATION

Asymmetric polymerization could be induced by an already formed optically active living prepolymer with one-handed screw sense helix conformation. The usually formed anionic active centre on the prepolymer could be changed to cationic, radical and even of Ziegler-Natta type. These living prepolymers with various kinds of active centre were all effective to induce a consequent asymmetric polymerization of a monomer which may be other than that in the prepolymer, to afford an optically active helical chain with the same screw sense as that of the prepolymer. Eight monomers have been used in the work. Optical rotation, circular dichroism and gelpermeation chromatography have been taken to prove the helix-induced asymmetric polymerization.

STUDY ON OPTICAL-ROTATORY OF HELIX POLYMER POLY(TRIPHENYLMETHYL METHACRYLATE)

The optical rotatory of helix polymer poly(triphenylmethyl methacrylate) (PTrMA) has been studied. The specific rotation of PTrMA is related with the length of helical chain linearly, while P(n)BAR<6 and P(n)BAR greater-than-or-equal-to 15. When P(n)BAR greater-than-or-equal-to 15, [alpha]D/20 = 1.6 P(n)BAR + 290-degrees. The contribution of each repeating unit to [alpha]D/20 is 1.6-degrees. In the 300-600 nm region, the ORD of PTrMA obeys both the Drude equation and Moffitt equation. The relationship between the [alpha]D of PTrMA and the solvent, concentration and temperature has also been investigated.

Donut-Shaped Fingerprint In Homologous Polypeptide Relationships-A Topological Feature Related To Pathogenic Structural Changes In Conformational Disease

Features of homologous relationship of proteins can provide us a general picture of protein universe, assist protein design and analysis, and further our comprehension of the evolution of organisms. Here we carried Out a Study of the evolution Of protein molecules by investigating homologous relationships among residue segments. The motive was to identify detailed topological features of homologous relationships for short residue segments in the whole protein universe. Based on the data of a large number of non-redundant Proteins, the universe of non-membrane polypeptide was analyzed by considering both residue mutations and structural conservation. By connecting homologous segments with edges, we obtained a homologous relationship network of the whole universe of short residue segments, which we named the graph of polypeptide relationships (GPR). Since the network is extremely complicated for topological transitions, to obtain an in-depth understanding, only subgraphs composed of vital nodes of the GPR were analyzed. Such analysis of vital subgraphs of the GPR revealed a donut-shaped fingerprint. Utilization of this topological feature revealed the switch sites (where the beginning of exposure Of previously hidden "hot spots" of fibril-forming happens, in consequence a further opportunity for protein aggregation is Provided; 188-202) of the conformational conversion of the normal alpha-helix-rich prion protein PrPC to the beta-sheet-rich PrPSc that is thought to be responsible for a group of fatal neurodegenerative diseases, transmissible spongiform encephalopathies. Efforts in analyzing other proteins related to various conformational diseases are also introduced. (C) 2009 Elsevier Ltd. All rights reserved.

Interaction between single molecules of Mac-1 and ICAM-1 in living cells: An atomic force microscopy study

The interaction between integrin macrophage differentiation antigen associated with complement three receptor function (Mac-1) and intercellular adhesion molecule-1 (ICAM-1), which is controlled tightly by the ligand-binding activity of Mac-1, is central to the regulation of neutrophil adhesion in host defense. Several "inside-out" signals and extracellular metal ions or antibodies have been found to activate Mac-1, resulting in an increased adhesiveness of Mac-1 to its ligands. However, the molecular basis for Mac-1 activation is not well understood yet. In this work, we have carried out a single-molecule study of Mac-1/ICAM-1 interaction force in living cells by atomic force microscopy (AFM). Our results showed that the binding probability and adhesion force of Mac-1 with ICAM-1 increased upon Mac-1 activation. Moreover, by comparing the dynamic force spectra of different Mac-1 mutants, we expected that Mac-1 activation is governed by the downward movement of its alpha 7 helix. (c) 2007 Elsevier Inc. All rights reserved.

倾斜沉积制备雕塑薄膜的研究进展

倾斜沉积是一种新型的薄膜沉积技术。通过制备过程中基片的旋转和倾斜,可以制备出斜柱状、之字形、螺旋状、S形以及C形等各种形状的雕塑薄膜。雕塑薄膜可以实现许多传统薄膜无法实现的光学性质,为光学薄膜的设计与制备开辟了新的途径。本文综述了雕塑薄膜的制备方法,分析了雕塑薄膜的结构特征及影响因素,并阐述了其在光学领域的广泛应用前景。

野生稻OrbHLH2基因的克隆及功能分析

　　bHLH（basic/helix-loop-helix）型的蛋白作为转录因子中的一个家族，控制一系列的生物学过程，例如细胞分化、细胞命运决定等。该家族的共同特点是具有一个bHLH型保守结构域，大约由60个氨基酸组成，在功能上划分为给两个部分：N端的碱性区域和C端的HLH区域，前者具有结合DNA的功能，后者参与了蛋白的二聚化，主要由疏水氨基酸组成。水稻中大多数的bHLH转录因子其功能还不清楚。 　　本论文利用同源克隆的方法，从水稻中得到与拟南芥ICE1同源性最高的基因，并命名为OsbHLH2，然后我们从野生稻中克隆到相关基因OrbHLH2。OrbHLH2 的cDNA全长为1961 bp，编码525个氨基酸。OrbHLH2与拟南芥、荠菜、毛果杨中推测的类ICE1蛋白之间的同源性分别达到46.1%、 45%、 41.2%，推测OrbHLH2可能是一个类ICE1蛋白。亚细胞定位实验结果表明，OrbHLH2定位于细胞核中；酵母自激活实验表明OrbHLH2具有自激活活性，因此推断OrbHLH2可能是一个转录因子。在水稻中对其组织表达模式进行分析发现，OsbHLH2在幼根、老根、幼茎、老茎、幼叶、老叶等组织中表达量极低，而在穗部的表达量很高，这暗示了OrbHLH2可能在水稻发育的特定阶段起重要作用；分析OsbHLH2对各种胁迫的响应，发现该基因在水稻中的表达不受低温、高盐、ABA等胁迫的诱导。 　　将OrbHLH2在拟南芥中异源超表达，转基因材料在发育上没有发现明显的表型改变。分析转基因拟南芥对不同胁迫的耐受性，结果表明：转基因拟南芥对高盐、渗透胁迫的抗性明显增强；分析一些抗逆标记基因的表达水平，发现与转基因拟南芥在高盐条件下DREB1A/CBF3、RD29A、COR15A和KIN1的表达量有不同程度的上调，暗示了在胁迫条件下OrbHLH2可能通过对DREB1A/CBF3途径中的基因的激活，来启动植物对逆境胁迫的响应，从而提高植物的抗逆性。该结果对于提高农作物的抗逆性具有潜在的应用价值。

高温和光照对光系统I结构与功能的影响

光合膜上包含有捕光并将光能转化为化学能所必需的四类跨膜蛋白复合体，即PSII、PSI、Cytb6f和ATP合成酶，其中PSI利用吸收的光能诱导电子从膜内侧的PC传递至相对一侧的铁氧还蛋白，被还原的铁氧还蛋白在FNR（Fd-NADP+氧化还原酶）的作用下生成NADPH，因此关于PSI的研究是光合作用研究领域中的重大问题。为了进一步阐明PSI的结构和功能，本论文分别研究了热对PSI的影响和光诱导的PSI核心复合物（CPI）的积累过程： 1.以菠菜PSI颗粒为材料研究了热处理对PSI复合物的降解和失活作用; 2.以衣藻叶绿素暗合成突变体y-1为材料研究了类囊体膜形成过程（即光诱导的转绿过程）中PSI中CPI的变化。另外，由于膜脂在光合作用中具有重要的功能，本论文还研究了y-1突变体转绿过程中光合膜脂、脂肪酸的变化。 一．应用光谱学、氧电极和变性电泳等技术研究了高温(25oC~80oC)对PSI结构和功能的影响，主要结果如下： 1． 在热处理过程中，683nm组分（主要归属于LHCI）的吸收峰强度有显著的下降并发生峰位蓝移现象，显示该组分对热处理最敏感，首先遭到破坏。 2． 77K荧光显示随着处理温度的升高，728 nm处的峰强和峰位均发生了明显的变化，F728-F720和F680的比率下降，说明热处理抑制了LHCI 680向LHCI 730以及反应中心的能量传递。 3． SDS-PAGE显示PSI核心蛋白PsaA/B亚基以及LHCI亚基在热处理情况下发生了不同程度的降解和聚合。为了能够显著地观察到热处理对PSI多肽降解的影响，实验采用了更高的温度处理方法，结果显示，90oC、100oC时PsaA/B亚基完全降解，而LHCI亚基仍有少量存在，说明PSI核心蛋白PsaA/B比LHCI亚基具有更高的热敏感性。 4． 推测热处理情况下可能发生的机制是，捕光天线首先从PSI反应中心分离，随后发生了反应中心光化学反应的抑制，直至最后多肽的严重降解。 5． 利用红外光谱技术（FT-IR）对PSI蛋白二级结构的研究显示，PSI颗粒在60oC以上时发生了明显的蛋白构象变化,且随着温度的升高蛋白构象的变化越来越大，表明PSI蛋白具有较高的热稳定性和热变性温度，PSI蛋白酰胺I带(1700~1600 cm-1)二级结构的解析表明热处理过程中二级结构的主要变化是α-helical的下降和β-sheet的增加。 6． 利用CD光谱技术研究了热处理对PSI色素微环境的影响，结果表明热处理破坏了PSI色素蛋白复合物中色素的蛋白微环境，归属于LHCI的Chlb（645 nm处组分）在较低的温度处理条件下(25~60oC)蛋白微环境即发生破坏;随着处理温度的升高（70和80 oC），478 nm处（主要归属于LHCI的Chlb）和498 nm（归属于类胡萝卜素）处的CD信号强度快速下降，说明在高温条件下LHCI比核心复合物更敏感。 7． 研究发现，PSI的摄氧活性随着处理温度的升高而显著下降，70oC时几乎完全失去摄氧能力，表明70oC时PSI复合物受到了严重的破坏，这可能是由于热处理过程中色素的蛋白微环境以及蛋白结构尤其是PSI核心蛋白PsaA/B中跨膜α-helix的构象发生了严重的变化。 二．主要运用温和电泳和蛋白印迹技术检测了暗培养4天(脱绿)的y-1突变体在光照诱发的转绿过程中PSI的核心色素蛋白复合物（CPI）及其叶绿素脱辅基蛋白PsaA/B的变化。 1． 暗培养4天的衣藻脱绿细胞中，PSI的主要色素蛋白复合物-CPI完全缺失，然而核心多肽PsaA/B仍有一定量的积累，同时检测不到P700的含量。 2． 当脱绿的y-1细胞转移至光照下时，伴随着叶绿素的合成，色素蛋白复合物CPI和PsaA/B脱辅基蛋白的合成也逐渐达到正常水平，说明叶绿素和PsaA/B蛋白进行组装并形成了具有功能的PSI反应中心,P700含量也得到了恢复。 3． 实验证明了光照是形成光合系统色素蛋白复合物的重要前提。同时发现，叶绿体基因编码的PSI核心多肽PsaA/B能够在暗条件下合成。而根据资料(Berends et al.,1987)报道，在豌豆、大麦的黄化体中不能合成PsaA/B蛋白，这可能是由于在脱绿的y-1细胞中叶绿体仍然具有相对完整的大小和形状，而在叶绿体的被膜上定位着多种与光合作用相关的酶系统。 三. 利用薄层层析及气相色谱分析技术对转绿期间y-1突变体光合膜脂和脂肪酸组成的含量变化进行了分析。结果表明： 1． 光照能够促进各种脂的积累并影响脂的组成，同时有利于脂肪酸脱饱和酶的激活。MGDG中脂肪酸不饱和程度明显升高，表现为16:0及18:1的下降，以及16:4，18：2和18:3（9，12，15）等的升高，说明光照促进了MGDG sn-2位的16:0脱饱和为16:4以及sn-1位的18：1脱饱和为18:3，也说明MGDG是脂肪酸脱饱和的重要底物。 2． 已有的资料（Ohnishi和Yamada，1980;1983）指出PG及其sn-2位的16:1（3t）的合成是光依赖的，而本实验中，在衣藻的黄化细胞中含有相当量的PG及其特有的16:1（3t）（22.80%），且转绿过程中变化并不十分显著。这可能是由于黄化的y-1细胞中叶绿体的形状并没有发生很大变化，说明叶绿体被膜上的相应酶系统才是PG合成的必需因素。 3． 相比于脱绿的y-1细胞，光照12小时后，各种脂中18：2的百分含量有显著的增加，这来源于18：2是脂肪酸脱饱和的重要中间产物。

A molecular model of braid-like DNA structure

The three-dimensional molecular models of DNA triple helices and triple-stranded brain-like structure were built up by molecular architecture, and their structural features and energy decomposition were examined. The results showed: (i) The base triplet is the element forming braid-like and triple helix DNA; (ii) Under specified conditions, DNA could form the triplet-stranded braid-like structure; (iii) DNA stability of the braid-like structure is less than that of the triple helix structure. (C) 1995 Academic Press Limited.

人胚胎干细胞定向分化为神经前体细胞

采用单层贴壁分化的方法在无血清条件下诱导同源饲养层培养的人胚胎干细胞定向分化,得到了高比例的神经前体细胞(97.5±0.83)%(P＜0.05).这些神经前体细胞具有分化为神经元、星形胶质细胞和少突胶质细胞的能力.在长期的传代培养中发现,随着培养时间的延长,nestin阳性的神经前体细胞比例下降,同时发育能力也发生了变化.在传代培养的早期,神经前体细胞发育为神经元的比例很高,几乎没有胶质细胞分化出来.随着培养时间的延长,胶质细胞的比例逐渐上升.这与体内神经系统的发育过程非常相似.进一步研究发现具有bHLH (basic helix-loop-helix) 结构域的转录因子neurogenein2(Ngn2) 和Olig2可能在这一变化中起重要作用.因此,人胚胎干细胞来源的神经前体细胞能够模拟体内神经发育的模式,为在体外研究人的神经发育和再生医学奠定了基础.