不同类型氨基酸网络参量与蛋白质折叠的关系

理论和实验研究表明,蛋白质天然拓扑结构对其折叠过程具有重要的影响．采用复杂网络的方法分析蛋白质天然结构的拓扑特征,并探索蛋白质结构特征与折叠速率之间的内在联系．分别构建了蛋白质氨基酸网络、疏水网、亲水网、亲水-疏水网以及相应的长程网络,研究了这些网络的匹配系数(assortativity coefficient)和聚集系数(clustering coefficient)的统计特性．结果表明,除了亲水-疏水网,上述各网络的匹配系数均为正值,并且氨基酸网和疏水网的匹配系数与折叠速率表现出明显的线性正相关,揭示了疏水残基间相互作用的协同性有助于蛋白质的快速折叠．同时,研究发现疏水网的聚集系数与折叠速率有明显的线性负相关关系,这表明疏水残基间三角结构(triangle construction)的形成不利于蛋白质快速折叠．还进一步构建了相应的长程网络,发现序列上间距较远的残基接触对的形成将使蛋白质折叠进程变慢．     

基于HNP三态模型及相对熵方法的蛋白质折叠研究

把20种氨基酸简化为3类:疏水氨基酸(hydrophobic,H)、亲水氨基酸(hydrophilic,P)及中性氨基酸(neutral,N),每个氨基酸简化为一个点,用其C!原子来代替.采用非格点模型,以相对熵作为优化函数,进行蛋白质三维结构预测.为了与基于相对熵方法的蛋白质设计工作进行统一,采用了新的接触强度函数.选用蛋白质数据库中的天然蛋白质作为测试靶蛋白,结果表明,采用该模型和方法取得了较好的结果,预测结构相对于天然结构的均方根偏差在0.30～0.70nm之间.该工作为基于相对熵及HNP模型的蛋白质设计研究打下了基础.     

大豆液泡膜H+-ATPase功能与构象关系的初步研究

大豆液泡膜V型H⁺-ATPase是ATPases中的一种,它在植物细胞的生长发育中有重要的作用.利用竹红菌乙素(HB）和KI这两种分别猝灭蛋白质疏水区域内源荧光和亲水区域内源荧光的荧光猝灭剂,在不同pH值、温度条件下对纯化的大豆液泡膜V型ATPase进行荧光猝灭实验,初步探讨了V型H⁺-ATPase的水解活性同其蛋白质折叠状态间的关系.研究表明,通过比较不同pH值、温度条件下蛋白质疏水区域和亲水区域内源荧光的荧光猝灭常数（K_SV）,发现当环境pH值、温度偏离酶的最适pH值和温度时,蛋白质的内源荧光强度降低且疏水区域和亲水区域内源荧光的荧光猝灭常数（K_SV）降低,说明伴随着酶的水解活性降低,蛋白质的折叠状态发生了变化.我们认为蛋白质在膜内的折叠状态变化是酶失活机制的一个重要方面,为植物的抗冻和抗盐研究提供了一定的参考.     

聚乙二醇修饰超氧化物歧化酶的初步研究

目的:对玉米超氧化物歧化酶(SOD)进行共价修饰,以提高其稳定性.方法:以分子量为6000Da的活化聚乙二醇(PEG)为修饰剂,对玉米超氧化物歧化酶(SOD)进行共价修饰,并确定最佳反应条件.将天然SOD与PEG-SOD分别进行热稳定性、酸碱稳定性及抗蛋白酶稳定性的比较实验.结果:在最佳反应时间10h、最佳反应温度4℃时PEG与SOD反应获得的PEG-SOD比天然SOD在热、酸、碱及抗酶解三方面的稳定性均有不同程度的提高.结论:玉米超氧化物歧化酶经PEG修饰后稳定性显著提高.     

真菌疏水蛋白的结构和功用

真菌疏水蛋白是一类具有强表面活性的分泌型小分子量蛋白质。疏水蛋白的重要特性是能在亲水—疏水界面通过自我组装形成一层紧密稳定的约10nm厚的两性蛋白膜。概述了疏水蛋白的结构和性质。总结了疏水蛋白的生理功能,并探讨它的各种应用。     

大仓鼠β2肾上腺素受体基因的套叠PCR法多点突变研究

对大仓鼠β1肾上腺素受体蛋白(β2 adrenergic receptor,β2AR)进行立体结构与疏水性分析.利用套叠,PCR法对β2AR基因进行多点突变,将保守跨膜域疏水氨基酸突变为正电荷亲水氨基酸,成功构建分别带有7个与3个突变氨基酸的原核突变表达载体.探讨了套叠,PCR的反应条件,为β2AR基因在体外的高量表达提供基础.     

质粒pUC18 DNA的螺线管型超螺旋结构

理论上,游离的超螺旋DNA可以采取两种结构形式：互缠式超螺旋和螺线管型超螺旋。前者早已被透射电子显微镜和原子力显微术的研究所证实,而后者却仍然缺乏足够的证据。使用温和的清亮裂解液法,从DNA拓扑酶野生型大肠杆菌HB101细胞抽提质粒pUC18 DNA。经CsCl-EB平衡密度梯度超离心分离获得超螺旋pUC18 DNA和松弛型pUC18 DNA(DNA Ⅱ）。纯化DNA分别用疏水必不容放亲水性溶剂系统的细胞色素单分子层展开技术制备电子显微镜标本。观察结果显示：在疏水性的甲酰胺－水展开系统中,DNA采取通常的互缠式结构;在含有1.5mmol/L醋酸铵的水介质中制备的超螺旋DNA标本,DNA采取线圈型结构,测得pUC18 DNA（单体）分子这种结构的外直径约为43.8nm,内直径约为2nm。在相同亲水介质中松弛型pUC18 DNA采取典型的螺线管型结构,其单体平均外直径约为53.1nm,内直径约为17.2nm。表明：在疏水介质中超螺旋DNA趋向于采取互缠式结构,而在亲水介质中DNA则要取螺线管型结构。DNA链之间可能存在非共价相互作用以维持这种结构。螺线管型结构可能是水溶液中的超螺旋DNA分子普遍的存在形式。     

神经节苷脂GM3对重建Ca 2+ -ATP酶构象的调节

应用稳态荧光和纳秒时间分辨瞬态荧光技术,以不同性质猝灭剂探测了神经节苷脂GM3诱发的Ca ²⁺-ATP酶构象的变化.结果显示,GM3可使重建的Ca ²⁺-ATP酶蛋白内源荧光寿命明显延长;并且能不同程度地减弱离子性猝灭剂碘化钾(I^-)和脂溶性猝灭剂竹红菌乙素(HB)对Ca ²⁺-ATP酶色氨酸(Trp)内源荧光的猝灭程度.进一步用时间分辨荧光猝灭动力学分析,当体系中有GM3存在时,HB对该蛋白不同荧光寿命组分的Trp内源荧光猝灭的幅度减小.猝灭常数(K_sv)明显降低.说明GM3依靠其亲水糖链和疏水的神经酰胺链作用,不仅可以改变重建Ca ²⁺-ATP酶蛋白嵌于膜脂疏水区内部的构象,使位于膜脂疏水区不同部位的Trp残基更加趋向排列于亲水-疏水域界面;而且还使Ca ²⁺-ATP酶亲水-疏水结构域之间更趋接近,致使整个酶蛋白分子呈现较“紧凑”的构象,表达较高的酶活力.     

GTPase循环保证了GTPase功能的实现

GTPase是一种传统的分子开关,多种GTPase之间有着共同的结构特点。近年的研究表明:在GTPase同GTP结合状态下,蛋白的亲水中心包含6条β段,并由疏水环和α螺旋相连。另外,还有5个区,均连接在蛋白同侧的疏水环上。这5个区分别用G-1～G-5表示,与GDP/GTP的相互交换是紧密相关的。     

环糊精葡萄糖转移酶的研究进展

环糊精葡萄糖转移酶在工业上用于生产环糊精.它可通过环化作用将淀粉转化成环糊精.由于环糊精具有一个亲水的外表面和一个疏水的内核,疏水的内核能包上非极性物质而溶于水中,所以在食品、化妆品、药品领域被广泛使用.综述环糊精葡萄糖转移酶近年在基因工程及蛋白质工程等方面的研究发展状况.     

Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis

It has now been over twenty years since a novel herpesviral genome was identified in Kaposi's sarcoma biopsies. Since then, the cumulative research effort by molecular biologists, virologists, clinicians, and epidemiologists alike has led to the extensive characterization of this tumor virus, Kaposi's sarcoma-associated herpesvirus(KSHV; also known as human herpesvirus 8(HHV-8)), and its associated diseases. Here we review the current knowledge of KSHV biology and pathogenesis, with a particular emphasis on new and exciting advances in the field of epigenetics. We also discuss the development and practicality of various cell culture and animal model systems to study KSHV replication and pathogenesis.     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.     

New or rare chromosome counts in Artemisia L. (Asteraceae, Anthemideae) and related genera from Kazakhstan

Fifteen chromosome counts of six Artemisia taxa and one species of each of the genera Brachanthemum, Hippolytia, Kaschgaria, Lepidolopsis and Turaniphytum are reported from Kazakhstan. Three of them are new reports, two are not consistent with previous counts and the remainder are confirmations of very scarce (one to four) earlier records. All the populations studied have the same basic chromosome number, x = 9, with ploidy levels ranging from 2x to 6x. Some correlations between ploidy level, morphological characters and distribution are noted.     

肝癌中HBV和HCV基因和抗原的分布及意义

采用原位分子杂交方法检测HCV RNA及HBV X基因;采用免疫组织化学方法研究HCV核心抗原,非结构区C33c抗原及HBxAg在肝细胞肝癌中的定位及分布.结果表明(1)HCV RNA、HBV X基因在肝细胞肝癌组织检出率分别为40%(55/136)和82%(112/136).HCV RNA定位于癌细胞的胞浆内,阳性细胞呈散在、灶状及弥漫分布三种形式;HBV X基因在肝癌细胞中的分布呈胞浆型、核型及核浆型,阳性细胞也呈上述三种分布形式;(2)HCV C33c抗原、核心抗原在肝细胞肝癌中的阳性率为81%(133/164)及86%(141/164).C33c抗原定位于癌细胞及肝细胞的胞浆内;核心抗原既定位于癌细胞核中,又可定位于胞浆中.C33c抗原阳性细胞以灶状分布为主;而核心抗原阳性细     

Selection with two alleles and complete dominance

For a plant selection model with frequency-independent viabilities, fertilities and selfing rates, it is shown that apart from global fixation, for certain parameter combinations a protected polymorphism and facultative fixation (either allele may become fixed according to initial frequencies) may both occur. Facultative fixation requires different selling rates for the dominant and recessive type. Protection of the polymorphism requires resource allocation for male and female function. In this connection the problem of purely genetically caused population extinction is discussed.
For general frequency dependence and regular segregation, the chances for establishment of a completely recessive gene are compared to those of a completely dominant gene. It is proven that the process of establishment of the recessive gene, despite a fitness advantage, may be considerably endangered by drift effects if random mating prevails. The recessive gene may reach the same effectivity in establishment as a dominant gene, only if the recessive homozygote mates exclusively with its own type during the period of establishment.