Membrane protein folding on the example of outer membrane protein A of <Emphasis Type="Italic">Escherichia coli</Emphasis>

The biophysical principles and mechanisms by which membrane proteins insert and fold into a biomembrane have mostly been studied with bacteriorhodopsin and outer membrane protein A (OmpA). This review describes the assembly process of the monomeric outer membrane proteins of Gram-negative bacteria, for which OmpA has served as an example. OmpA is a two-domain outer membrane protein composed of a 171-residue eight-stranded -barrel transmembrane domain and a 154-residue periplasmic domain. OmpA is translocated in an unstructured form across the cytoplasmic membrane into the periplasm. In the periplasm, unfolded OmpA is kept in solution in complex with the molecular chaperone Skp. After binding of periplasmic lipopolysaccharide, OmpA insertion and folding occur spontaneously upon interaction of the complex with the phospholipid bilayer. Insertion and folding of the -barrel transmembrane domain into the lipid bilayer are highly synchronized, i.e. the formation of large amounts of -sheet secondary structure and -barrel tertiary structure take place in parallel with the same rate constants, while OmpA inserts into the hydrophobic core of the membrane. In vitro, OmpA can successfully fold into a range of model membranes of very different phospholipid compositions, i.e. into bilayers of lipids of different headgroup structures and hydrophobic chain lengths. Three membrane-bound folding intermediates of OmpA were discovered in folding studies with dioleoylphosphatidylcholine bilayers. Their formation was monitored by time-resolved distance determinations by fluorescence quenching, and they were structurally distinguished by the relative positions of the five tryptophan residues of OmpA in projection to the membrane normal. Recent studies indicate a chaperone-assisted, highly synchronized mechanism of secondary and tertiary structure formation upon membrane insertion of -barrel membrane proteins such as OmpA that involves at least three structurally distinct folding intermediates.     

The mass recognizing property of DLC film for formic acid vapors

The carbon films are prepared by r. f. plasma method with n-butylamine as carbon source. The analysis of Raman spectrosewpy shows that this kind of carbon film has diamond-like structure, and IR spectroscopy measurement indicats that there are SP² bonding, SP³ bonding and amino-group in the film. It is the existence of amino-group and hydrogen atom that cause the amorphous structure and the deformation of bonding to increase, thus leading the Raman spectrum to form a broad absorption band. The quartz crystal microbalance (QCM) deposited with this kind of carbon film as recognizing coating is very sensitive to formic acid vapors. This QCM sensor has good reproducibility, high stability, rapid response and long lifetime.     

人类乙型肝炎样病毒核心蛋白中第7位疏水性氨基酸重复肚段区域的突变可以抑制病毒核衣壳的组装

人类乙型肝炎病毒的核衣壳由核心蛋白的二聚体所组成．但是,核心蛋白亚单位与亚单位之间相互作用的机制至今尚不清楚．研究发现,在人类乙型肝炎样病毒──土拨鼠肝炎病毒（WHV）核心蛋白的氨基端,存在着4个保守的疏水氨基酸残基（氨基酸位置101～102）．它们分别是亮氨酸101,亮氨酸108,缬氨酸115和苯丙氨酸122．这4个疏水氨基酸残基以每隔6个氨基酸残基而重复出现1次．它们被称为“第7位疏水性氨基酸重复肽段（hhr）”．由于蛋白质中的疏水键往往在蛋白质的相互作用中起重要作用,因此就在培养细胞系统中研究WHV核心蛋白的hhr区域在…     

玉米巯基蛋白酶抑制剂的纯化及部分性质

从玉米种子纯化的两种巯基蛋白酶抑制剂（ＣＰＩ－Ｉ和ＣＰＩ－Ⅱ）分子量分别为９５００和１３０００,经们都只抑制巯基蛋白酶的水解活性,而对丝氨酸蛋白酶则无抑制作用,属于巯基蛋白酶水解抑制剂,它们在ｐＨ３．０～１１．０或１００℃温度范围内保有１００％的抑制木瓜蛋白的抑制活性,表明在这些外界条件下其分子非常稳定。     

抗冻蛋白及其对冰晶生长的影响

抗冻蛋白具有特殊的热迟滞性质，即其冰点低于熔点，且能抑制冰晶的生长．本文综述了在耐寒鱼、昆虫体内以及最近二三年在植物、真菌、细菌等生物中发现的抗冻蛋白，分析其结构及其对冰晶生长的影响，并寻求抗冻蛋白在细胞、生物组织的低温保存中可能的应用途径．     

用^211At和^131I标记蛋白质的研究

报道了砹—211和碘—131标记蛋白质的方法.通过过氧化氢或氯胺T直接氧化制备,使用凝胶色谱从反应产物中分离标记蛋白质,相对法比较放射性计数测定标记产率,过氧化氢适用于~(211)At标记蛋白质,氯胺T有利于~(131)I标记蛋白质.8次实验的结果表明,用过氧化氢氧化标记的~(211)At牛血清白蛋白产率96.4％,氯胺T氧化标记的~(?)I牛血清白蛋白产率66.1％.间接法标记蛋白质,放射性核素~(211)At同对氨基苯甲酸反应获得对—~(211)At—苯甲酸,经乙醚萃取和高效液体色谱分离,然后再偶联到免疫球蛋白或牛血清白蛋白上。动物实验结果表明,此种结合的标记蛋白质在体内稳定,标记率不低于初始~(211)At放射性活度的40%.     

一种简便快速工艺制备重组人胸腺肽α1

将构建的含有胸腺肽α₁融合蛋白的编码基因插入表达质粒pET28a(+)中，并在大肠杆菌BL21中进行表达，该菌经IPTG诱导融合蛋白高表达后，离心收集菌体，超声波破碎，包含体裂解，目标蛋白质的体外变性复性后，经DEAE-Sepharose Fast Flow阴离子交换层析纯化，每升菌液中可获得260mg融合蛋白。经重组肠激酶酶切反应、Ni-Sepharose亲和层析，Sephadex G-25柱纯化后，得到了纯度达97%的重组人胸腺肽α₁，该纯化工艺简单快速，经三步层析即可得到纯度达97%的重组人胸腺肽α₁，且产量达82mg/L，为大批量用细菌表达重组人胸腺肽α₁及纯化提供了参考。     

肺炎患儿一氧化氮与GMP—140水平变化及其临床意义

为探讨血清一氧化氮 (NO)和血浆α -颗粒膜蛋白GMP - 14 0在小儿肺炎中的作用及其临床意义 ,分别采用硝酸酶还原法和ELISA双抗体夹心法测定 4 1例小儿肺炎和 2 3例正常对照者血清一氧化氮和血浆GMP - 14 0 .结果表明 :肺炎组 (包括重症和轻症组 )血清NO水平较对照组显著性升高 (P <0 .0 1) ,重症组血清NO水平较轻症组亦显著性升高 (P <0 .0 1) ;肺炎组 (包括重症和轻症组 )血浆GMP - 14 0均较对照组显著性升高 (P <0 .0 1) ;且肺炎患儿血清NO水平与血浆GMP - 14 0含量呈显著正相关 (r=0 .73,P <0 .0 1) .提示肺炎患儿体内存在血小板活化 ,NO和血小板活化可能共同参与了肺炎的发展过程     

传染性法氏囊病病毒分子生物学研究的一些进展

对IBDV近年来的分子生物学方面的研究进展进行概况，主要包括IBDv的基因组结构及理化特性、病毒蛋白、不同型IBDV变异的分子基础和分子生物学诊断技术等，以探讨利用病毒重要基因核酸序列的差异进行IBDV分子流行病学研究及病毒各致病型快速鉴别诊断的可能性．     

用离散量预测原核生物蛋白质的亚细胞位置

基于不同亚细胞位置中蛋白质的氨基酸组成及序列信息不同这一观点，以单个氨基酸含量及两两组合氨基酸含量为信息构成离散源，分别计算了原核生物蛋白质三类亚细胞位置的标准离散量D(Z)，D(Xp)，D(Xc)．利用离散增量的概念预测蛋白质的亚细胞位置，它是由这个蛋白质的离散量D(X)与三个标准离散量D(Xc)，D(Xp)，D(Xc)之间离散增量的最小值所决定的．采用Self—consistency检验和Jack—knife检验方法，给出了选择五组不同信息作为离散源中参数时的预测结果．与现有的方法比较，发现用Jack—knife检验法预测extracellular类蛋白质时，给出的离散量方法能够给出最好的预测性能，结果也表明提取更多有效的序列信息是提高预测精度的关键．