Aromatic-aromatic interaction: a mechanism of protein structure stabilization

Analysis of neighboring aromatic groups in four biphenyl peptides or peptide analogs and 34 proteins reveals a specific aromatic-aromatic interaction. Aromatic pairs (less than 7 A between phenyl ring centroids) were analyzed for the frequency of pair type, their interaction geometry (separation and dihedral angle), their nonbonded interaction energy, the secondary structural locations of interacting residues, their environment, and their conservation in related molecules. The results indicate that on average about 60 percent of aromatic side chains in proteins are involved in aromatic pairs, 80 percent of which form networks of three or more interacting aromatic side chains. Phenyl ring centroids are separated by a preferential distance of between 4.5 and 7 A, and dihedral angles approaching 90 degrees are most common. Nonbonded potential energy calculations indicate that a typical aromatic-aromatic interaction has energy of between -1 and -2 kilocalories per mole. The free energy contribution of the interaction depends on the environment of the aromatic pair. Buried or partially buried pairs constitute 80 percent of the surveyed sample and contribute a free energy of between -0.6 and -1.3 kilocalories per mole to the stability of the protein's structure at physiologic temperature. Of the proteins surveyed, 80 percent of these energetically favorable interactions stabilize tertiary structure, and 20 percent stabilize quaternary structure. Conservation of the interaction in related molecules is particularly striking.     

植物低温诱导蛋白的研究进展

低温能够诱导植物基因的表达从而合成新的蛋白质,这些蛋白质具有增强细胞抗冰冻脱水能力、保护酶行使正常功能和代谢调节功能及稳定细胞膜等作用。植物低温诱导蛋白及其理化性质与抗冻关系一直是国内外的研究热点。综述了抗冻蛋白、脱水蛋白和热激蛋白3种低温诱导蛋白的最新研究进展及与植物抗冻性的关系。     

板蓝根饮片糖基化蛋白纳米颗粒的构建与表征

从板蓝根饮片中分离出糖基化蛋白,体外构建纳米颗粒,并对所形成胶体的理化性质和生物活性进行表征。经SDS-PAGE鉴定板蓝根饮片粗提液中存在3个主要的糖基化蛋白,用这些蛋白构建的纳米颗粒的粒径约为50 nm。MDCK细胞试验表明,蛋白纳米颗粒具有较强的抗病毒能力。     

选择素及其配体在哺乳动物胚胎着床过程中的作用

选择素是一种非免疫来源的多价糖类结合蛋白,为细胞粘附分子(celladhesionmolecules,cAMs)超家族的一员,选择素家族有3个结构类似的成员:E-选择素、L-选择素、P-选择素,它们在炎症发生时可介导白细胞与血管内皮细胞之间、白细胞与白细胞及白细胞与血小板之间的粘附。近年来研究发现,选择素及其配体还在精卵识别、滋养层细胞和子宫内膜的相互识别、滋养层细胞侵入、胎盘形成等过程中发挥重要作用。在此,主要对E-选择素、L-选择素及它们的配体在哺乳动物胚胎着床过程中发挥的作用及其表达调节作一综述。     

Glycosylation and the immune system

Almost all of the key molecules involved in the innate and adaptive immune response are glycoproteins. In the cellular immune system, specific glycoforms are involved in the folding, quality control, and assembly of peptide-loaded major histocompatibility complex (MHC) antigens and the T cell receptor complex. Although some glycopeptide antigens are presented by the MHC, the generation of peptide antigens from glycoproteins may require enzymatic removal of sugars before the protein can be cleaved. Oligosaccharides attached to glycoproteins in the junction between T cells and antigen-presenting cells help to orient binding faces, provide protease protection, and restrict nonspecific lateral protein-protein interactions. In the humoral immune system, all of the immunoglobulins and most of the complement components are glycosylated. Although a major function for sugars is to contribute to the stability of the proteins to which they are attached, specific glycoforms are involved in recognition events. For example, in rheumatoid arthritis, an autoimmune disease, agalactosylated glycoforms of aggregated immunoglobulin G may induce association with the mannose-binding lectin and contribute to the pathology.     

SPME/GC-MS法分析不同荔枝品种果实中的香气成分

采用SPME/GC-MS法对3个荔枝品种果实香气成分进行分析鉴定。结果表明,3个荔枝品种共检测出69种芳香物质,其中,烯类47种、醇类6种、醚类4种、酯类3种、苯类3种,烷类1种、酮类1种、其他4种,它们构成3种荔枝主要的香气成分;3个荔枝品种在香气组成和含量上有所差异,岭丰糯、糯米糍、怀枝中分别含有20种、11种、11种特有香气成分;其中,3种荔枝共有的香气成分有13种,分别是β-香叶烯、伞花烯、D-柠檬烯、β-罗勒烯、2-蒈烯、β-香茅醇甲醚、橙花醇甲醚、1-甲氧基-3,7-二甲基-2,6-辛二烯、古巴烯、β-榄香烯、石竹烯、α-石竹烯、δ-杜松烯,但其相对含量有所差异。     

东北地区10份李种质资源果实香气成分分析

【目的】以东北地区10份李种质资源果实为供试材料,进行香气成分分析及特异香气成分精准鉴定,明确起主要贡献作用的李果实特异香气成分,筛选东北地区富含香气的优异李资源,为李香气高效育种和分子水平基础研究提供数据参考。【方法】应用顶空固相微萃取-气相色谱质谱联用技术,对李果实的香气成分进行测定,利用香气强度值（OAV）和主成分分析（PCA）对李果实中的特异香气成分进行鉴定和分析。【结果】10份李种质资源果实共检测出香气成分63种,其中,共有香气成分有9种,分别为右旋柠檬烯、(E)-2-己烯醛、(E)-2-辛烯醛、(E)-2-壬烯醛、癸醛、2-壬酮、2,6,6-三甲基-2-环己烯-1,4-二酮、2,4-二叔丁基苯酚、伞花烃。‘牡红甜李’‘绥棱红’‘跃进李’‘红干核’‘黄干核’‘幸运’‘大玫瑰’和‘四丰李’香气的主要种类为醛类,‘牛心李’和‘香蕉李’香气的主要种类为酯类。香气PCA结果表明,10份李资源可分为3类,‘牡红甜李’‘绥棱红’‘跃进李’‘红干核’‘黄干核’‘幸运’‘大玫瑰’和‘四丰李’为一类,‘香蕉李’和‘牛心李’各自为一类。香气OAV结果显示,10份李资源共有的特异香气成分是(E)-2-己烯醛和2-壬酮,‘牛心李’特有的特异香气成分是丁酸乙酯、癸酸乙酯和乙酸异戊酯,‘香蕉李’特有的特异香气成分是乙酸丁酯和丙酸己酯,‘牡红甜李’特有的特异香气成分是α-蒎烯,‘绥棱红’特有的特异香气成分是(E)-2-庚烯醛。【结论】β-紫罗酮是东北地区分布的‘牡红甜李’‘绥棱红’‘跃进李’‘红干核’‘黄干核’‘香蕉李’和‘四丰李’特有的特异香气成分。‘牡红甜李’‘牛心李’和‘香蕉李’特异香气成分丰富,为李优异香气资源。     

Independently evolved virulence effectors converge onto hubs in a plant immune system network

Plants generate effective responses to infection by recognizing both conserved and variable pathogen-encoded molecules. Pathogens deploy virulence effector proteins into host cells, where they interact physically with host proteins to modulate defense. We generated an interaction network of plant-pathogen effectors from two pathogens spanning the eukaryote-eubacteria divergence, three classes of Arabidopsis immune system proteins, and ~8000 other Arabidopsis proteins. We noted convergence of effectors onto highly interconnected host proteins and indirect, rather than direct, connections between effectors and plant immune receptors. We demonstrated plant immune system functions for 15 of 17 tested host proteins that interact with effectors from both pathogens. Thus, pathogens from different kingdoms deploy independently evolved virulence proteins that interact with a limited set of highly connected cellular hubs to facilitate their diverse life-cycle strategies.     

合理降低油品芳香烃含量的重要性

分析了油品中烷烃、环烷烃、芳香烃、烯烃的理化性能及其在油品中的作用，指出了芳香烃对石油产品的抗爆性、抗氧安定性、燃烧性、生炭性、十六烷值、热值的影响。分析结果表明，油品芳香烃含量过多，不仅污染大气，而且还严重影响发动机的工作性能。提出了合理降低油品中芳香烃含量的建议和措施。     

城市污泥中有机酸在厌氧消化过程中的稳定性差异

研究了厌氧消化作用对深圳污泥中有机酸的降解作用,消化过程中有机酸的稳定性受分子结构决定,羟基酸〈烯酸〈正烷酸〈芳香酸〈甾酸,具有稠环、苯环和共轭双键结构者稳定性较高,而含有羟基和孤立双键者稳定性较低,且羟基基团越多,结构越不稳定,厌氧消化对能选择降解高碳数羟基本是选择保存低碳数基酸,某些民政部下,有机酸的稳定悸也可能受生物代谢因素的影响。     

Colorectal cancer in mice genetically deficient in the mucin Muc2

The gastrointestinal tract is lined by a layer of mucus comprised of highly glycosylated proteins called mucins. To evaluate the importance of mucin in intestinal carcinogenesis, we constructed mice genetically deficient in Muc2, the most abundant secreted gastrointestinal mucin. Muc2-/- mice displayed aberrant intestinal crypt morphology and altered cell maturation and migration. Most notably, the mice frequently developed adenomas in the small intestine that progressed to invasive adenocarcinoma, as well as rectal tumors. Thus, Muc2 is involved in the suppression of colorectal cancer.     

Binding of benzo[a]pyrene 7,8-diol-9,10-epoxides to DNA, RNA, and protein of mouse skin occurs with high stereoselectivity

The formation, stereostructure, and cellular reactions of the 7,8-diol-9,10-epoxide metabolites of the carcinogen benzo[a]pyrene have been examined after topical application of benzo[a]pyrene to the skin of mice. In this known target tissue, polymer adducts from diastereomeric diol epoxides, (+)-(7S, 8R, 9R, 10R) and (+)-(7R, 8S, 9R, 10R), were formed stereospecifically from their corresponding 7,8-dihydrodiols. Both diol epoxides bind with proteins, RNA, and DNA in vivo. For the nucleic acids, binding occurs preferentially at the 2-amino group of guanine in cellular RNA and DNA in vivo. Methods for establishing the structure of the cellular adducts as well as the possible biological implications of their formation are discussed.     

Protein nanoarrays generated by dip-pen nanolithography

Dip-pen nanolithography was used to construct arrays of proteins with 100- to 350-nanometer features. These nanoarrays exhibit almost no detectable nonspecific binding of proteins to their passivated portions even in complex mixtures of proteins, and therefore provide the opportunity to study a variety of surface-mediated biological recognition processes. For example, reactions involving the protein features and antigens in complex solutions can be screened easily by atomic force microscopy. As further proof-of-concept, these arrays were used to study cellular adhesion at the submicrometer scale.     

Active disruption of an RNA-protein interaction by a DExH/D RNA helicase

All aspects of cellular RNA metabolism and the replication of many viruses require DExH/D proteins that manipulate RNA in a manner that requires nucleoside triphosphates. Although DExH/D proteins have been shown to unwind purified RNA duplexes, most RNA molecules in the cellular environment are complexed with proteins. It has therefore been speculated that DExH/D proteins may also affect RNA-protein interactions. We demonstrate that the DExH protein NPH-II from vaccinia virus can displace the protein U1A from RNA in an active adenosine triphosphate-dependent fashion. NPH-II increases the rate of U1A dissociation by more than three orders of magnitude while retaining helicase processivity. This indicates that DExH/D proteins can effectively catalyze protein displacement from RNA and thereby participate in the structural reorganization of ribonucleoprotein assemblies.     

Assembly of cell regulatory systems through protein interaction domains

The sequencing of complete genomes provides a list that includes the proteins responsible for cellular regulation. However, this does not immediately reveal what these proteins do, nor how they are assembled into the molecular machines and functional networks that control cellular behavior. The regulation of many different cellular processes requires the use of protein interaction domains to direct the association of polypeptides with one another and with phospholipids, small molecules, or nucleic acids. The modular nature of these domains, and the flexibility of their binding properties, have likely facilitated the evolution of cellular pathways. Conversely, aberrant interactions can induce abnormal cellular behavior and disease. The fundamental properties of protein interaction domains are discussed in this review and in detailed reviews on individual domains at Science's STKE at http://www.sciencemag.org/cgi/content/full/300/5618/445/DC1.