Study of molecular events in cells by fluorescence correlation spectroscopy

To understand processes in a living cell, sophisticated and creative approaches are required that can be used for gathering quantitative information about large number of components interacting across temporal and spatial scales without major disruption of the integral network of processes. A physical method of analysis that can meet these requirements is fluorescence correlation spectroscopy (FCS), which is an ultrasensitive and non-invasive detection method capable of single-molecule and real-time resolution. Since its introduction about 3 decades ago, this until recently emerging technology has reached maturity. As commercially built equipment is now available, FCS is extensively applied for extracting biological information from living cells unattainable by other methods, and new biological concepts are formulated based on findings by FCS. In this review, we focus on examples in the field of molecular cellular biology. The versatility of the technique in this field is illustrated in studies of single-molecule dynamics and conformational flexibility of proteins, and the relevance of conformational flexibility for biological functions regarding the multispecificity of antibodies, modulation of activity of C5a receptors in clathrin-mediated endocytosis and multiplicity of functional responses mediated by the p53 tumor suppressor protein; quantitative characterization of physicochemical properties of the cellular interior; protein trafficking; and ligand-receptor interactions. FCS can also be used to study cell-to-cell communication, here exemplified by clustering of apoptotic cells via bystander killing by hydrogen peroxide.Received 15 July 2004; received after revision 13 October 2004; accepted 12 November 2004     

Proteolytic generation and aggregation of peptides from transmembrane regions: lung surfactant protein C and amyloid β-peptide

The formation of amyloid fibrils is associated with several devastating diseases in humans and animals, including e.g. Alzheimers disease (AD) and the spongiform encephalopathies. Here, we review and discuss the current knowledge on two amyloid peptides: lung surfactant protein C (SP-C) and the amyloid -peptide (A), implicated in human lung disease and in AD, respectively. Both these hydrophobic peptides are derived from the transmembrane region of their precursor protein, and can transit from a monomeric -helical state to a -sheet fibril. The helices of SP-C and A are composed of amino acid residues with inherently higher propensities for strand than helix conformation. Their helical states are stabilized by a membrane environment, and loss of membrane association thus promotes structural conversion and fibril formation. We speculate that the loss of structural context for sequences with a high propensity for formation of sheets may be a common feature of amyloid formation in general.Received 9 July 2003; received after revision 15 August 2003; accepted 3 September 2003     

Canonical protein inhibitors of serine proteases

Serine proteases and their natural protein inhibitors are among the most intensively studied protein complexes. About 20 structurally diverse inhibitor families have been identified, comprising -helical, sheet, and / proteins, and different folds of small disulfide-rich proteins. Three different types of inhibitors can be distinguished based on their mechanism of action: canonical (standard mechanism) and non-canonical inhibitors, and serpins. The canonical inhibitors bind to the enzyme through an exposed convex binding loop, which is complementary to the active site of the enzyme. The mechanism of inhibition in this group is always very similar and resembles that of an ideal substrate. The non-canonical inhibitors interact through their N-terminal segment. There are also extensive secondary interactions outside the active site, contributing significantly to the strength, speed, and specificity of recognition. Serpins, similarly to the canonical inhibitors, interact with their target proteases in a substrate-like manner; however, cleavage of a single peptide bond in the binding loop leads to dramatic structural changes.Received 28 March 2003; received after revision 12 May 2003; accepted 16 May 2003     

醚—醚桥键间与醚—酮桥键间苯环运动的AM1量子化学研究

本文应用ＡＭ１半经验量子化学计算研究了醚－醚桥键间及醚－酮桥键间苯环的运动状况．计算结果表明，苯环在这两类桥键间的运动曲线十分相似，有一个宽度相近且具有较小势能的区域及最优构象均位于苯环与分子骨架成夹角４０°左右．从理论上解释了两类桥键在结晶行为上的等同性     

ConformationsofCytochromeP─450Modelsby1Dand2DNMR

ＣｏｎｆｏｒｍａｔｉｏｎｓｏｆＣｙｔｏｃｈｒｏｍｅＰ┐４５０Ｍｏｄｅｌｓｂｙ１Ｄａｎｄ２ＤＮＭＲＮｉｎｇＹｏｎｇｃｈｅｎｇ（宁永成）＋，ＹｕａｎＬｉｈｕａ（袁立华），ＷａｎｇＦｅｎｇｙａｎ（王丰彦）＋，ＹｕａｎＨａｏｄａｎ（袁浩丹）＋，ＣｈｅｎＳｈ...     

含有修饰SpA的重组生物膜的表征

通过ＬＢ膜技术将硬脂酸酯修饰的ＳｐＡ嵌入到气液界面的磷脂膜中，并沉积于疏水石英表面形成重组双层生物膜。此重组膜可作为免疫球蛋白的能诱导膜。结果表明，修饰ＳｐＡ表面硬脂酸数目的多少是影响该蛋白构象变化的主要原因。当共嵌入到磷脂单分子膜中时，膜中蛋白质密度增加，且呈现良好的成膜特性，重组膜中ＳｐＡ的活性下降与理解旨酸的修饰及ＳｐＡ在膜中嵌入作用有关。本文还讨论了膜中结合ＩｇＧ的状态。     

胆碱酯酶催化反应的量子化学研究——残基作用对乙酰胆碱构象及其水解反应的影响

采用量子化学ＳＣＦＬＣＡＯ－ＭＯＭＮＤＯ和ＣＮＤＯ／２方法，考查了胆碱酯酶活性基团的存在对底物乙酰胆碱的构象稳定性的影响．同时分析了活性基团作用下乙酰胆碱的水解部位化学键强度、净电荷分布等的相对变化规律，探讨了活性构象和稳定构象的联系     

乙醇对鲍鱼碱性磷酸酶活力与构象的影响

以乙醇为效应物研究对鲍鱼碱性磷酸酶(ALP)活力影响的结果表明．酶的剩余活力随着乙醇浓度增大而迅速下降，乙醇浓度40％可使酶活力完全丧失．说明乙醇对鲍鱼ALP有明显的失活作用，JG50为13％．含较低浓度乙醇(30％)的失活过程是可逆的反应．测定乙醇对酶的失活作用机理．结果表明乙醇对鲍鱼ALP的失活作用是非竞争性机制，说明底物存在不影响乙醇对酶的失活作用．应用荧光光谱、紫外吸收光谱研究鲍鱼ALP经乙醇微扰后的分子构象变化，发现乙醇对酶分子构象有显的影响，酶的内源荧光强度随乙醇浓度增大而增强．荧光发射峰逐渐发生红移．紫外吸收光谱在276nm吸收峰随乙醇浓度增大而增强．这些结果表明．酶蛋白分子中的生色基团残基的微环境发生变化．     

基于模拟退火算法的蛋白质空间结构预测

模拟退火是一种通用的启发式优化算法，将模拟退火思想用于求解蛋白质结构预测问题，计算结果表明利用SA算法得到的解优于目前常用的遗传算法和MonteCarlo方法．