Microtubule-associated protein MAP2 shares a microtubule binding motif with tau protein

The microtubule-associated protein MAP2 is a prominent large-sized component of purified brain microtubules that, like the 36- to 38-kilodalton tau proteins, bears antigenic determinants found in association with the neurofibrillary tangles of Alzheimer's disease. The complete sequence of mouse brain MAP2 was determined from a series of overlapping cloned complementary DNAs. The sequence of the carboxyl-terminal 185 amino acids is very similar (67 percent) to a corresponding region of tau protein, and includes a series of three imperfect repeats, each 18 amino acids long and separated by 13 or 14 amino acids. A subcloned fragment spanning the first two of the 18-amino acid repeats was expressed as a polypeptide by translation in vitro. This polypeptide copurified with microtubules through two successive cycles of polymerization and depolymerization, whereas a control polypeptide derived from the amino-terminal region of MAP2 completely failed to copurify. These data imply that the carboxyl-terminal domain containing the 18-amino acid repeats constitutes the microtubule binding site in MAP2. The occurrence of these repeats in tau protein suggests that these may be a general feature of microtubule binding proteins.     

竹材加工剩余物耐盐性高吸水保水材料的制备及性能

竹材加工剩余物是丰富的可再生资源,且在培肥土壤、改善土壤微量元素等方面有积极作用。利用竹材加工剩余物制备高吸水保水材料,不仅使天然资源得到有效利用,还可以降低高吸水保水材料的成本,增加材料的复合功能。利用竹材加工剩余物为原材料,接枝丙烯酸、丙烯酰胺单体制备耐盐性高吸水性树脂。以过硫酸钾作为引发剂,通过将单体丙烯酸（AA）在一定条件下接枝到竹纤维上的共聚反应合成吸水性树脂,研究单体中和度、竹粉加入与否、引发剂用量、单体用量、碱液种类等对接枝共聚产物吸水树脂的吸水率的影响。碱液种类选取300.00 gkg－1氢氧化钠水溶液、丙烯酸中和度为60.0%,引发剂用量为0.04 g,引发剂与单体丙烯酸同时加入、单体丙烯酸的用量为8.0 mL时吸水率高,达718.20 gg－1。图1表4参12     

Evidence from cassette mutagenesis for a structure-function motif in a protein of unknown structure

The three-dimensional structure of most enzymes is unknown; however, many enzymes may have structural motifs similar to those in the known structures of functionally related enzymes. Evidence is presented that an enzyme of unknown structure [Ile-transfer RNA (tRNA) synthetase] may share a functionally important structural motif with an enzyme of related function (Tyr-tRNA synthetase). This approach involves (i) identifying segments of Ile-tRNA synthetase that have been unusually conserved during evolution, (ii) predicting the function of one such segment by assuming a structural relation between Ile-tRNA synthetase and Tyr-tRNA synthetase, and (iii) testing the predicted function by mutagenesis and subsequent biochemical analysis. Random mutations were introduced by cassette mutagenesis into a ten-amino-acid segment of Ile-tRNA synthetase that was predicted to be involved in the formation of the binding site for isoleucine. Few amino acid substitutions appear to be tolerated in this region. However, one substitution (independently isolated twice) increased the Michaelis constant Km for isoleucine in the adenylate synthesis reaction by greater than 6000-fold, but had little effect on the Km for adenosine triphosphate, the apparent Km for tRNA, or the rate constant kcat.     

Cell-adhesive motif in region II of malarial circumsporozoite protein

The segment of the malarial circumsporozoite (CS) protein designated Region II is highly conserved among different malarial species. A similar sequence is also present in several other proteins, including thrombospondin, properdin, and a blood-stage antigen of Plasmodium falciparum. By means of peptides synthesized from sequences of the Plasmodium vivax CS protein in the vicinity of Region II, it was found that two overlapping 18- to 20-amino acid peptides promoted the adhesion of a variety of human hematopoietic cell lines. The amino acid sequence valine-threonine-cysteineglycine (VTCG), contained within this common motif, was shown to be the critical sequence for the observed cell-adhesive properties.     

Design and evolution of new catalytic activity with an existing protein scaffold

The design of enzymes with new functions and properties has long been a goal in protein engineering. Here, we report a strategy to change the catalytic activity of an existing protein scaffold. This was achieved by simultaneous incorporation and adjustment of functional elements through insertion, deletion, and substitution of several active site loops, followed by point mutations to fine-tune the activity. Using this approach, we were able to introduce beta-lactamase activity into the alphabeta/betaalpha metallohydrolase scaffold of glyoxalase II. The resulting enzyme, evMBL8 (evolved metallo beta-lactamase 8), completely lost its original activity and, instead, catalyzed the hydrolysis of cefotaxime with a (kcat/Km)app of 1.8 x 10(2) (mole/liter)(-1) second(-1), thus increasing resistance to Escherichia coli growth on cefotaxime by a factor of about 100.     

Conformational control of the Ste5 scaffold protein insulates against MAP kinase misactivation

Cells reuse signaling proteins in multiple pathways, raising the potential for improper cross talk. Scaffold proteins are thought to insulate against such miscommunication by sequestering proteins into distinct physical complexes. We show that the scaffold protein Ste5, which organizes the yeast mating mitogen-activated protein kinase (MAPK) pathway, does not use sequestration to prevent misactivation of the mating response. Instead, Ste5 appears to use a conformation mechanism: Under basal conditions, an intramolecular interaction of the pleckstrin homology (PH) domain with the von Willebrand type A (VWA) domain blocks the ability to coactivate the mating-specific MAPK Fus3. Pheromone-induced membrane binding of Ste5 triggers release of this autoinhibition. Thus, in addition to serving as a conduit guiding kinase communication, Ste5 directly receives input information to decide if and when signal can be transmitted to mating output.     

Combinatorial synthesis of peptide arrays onto a microchip

Arrays promise to advance biology through parallel screening for binding partners. We show the combinatorial in situ synthesis of 40,000 peptide spots per square centimeter on a microchip. Our variant Merrifield synthesis immobilizes activated amino acids as monomers within particles, which are successively attracted by electric fields generated on each pixel electrode of the chip. With all different amino acids addressed, particles are melted at once to initiate coupling. Repetitive coupling cycles should allow for the translation of whole proteomes into arrays of overlapping peptides that could be used for proteome research and antibody profiling.     

嫁接对盐胁迫下西瓜幼苗生长和可溶性蛋白表达的影响

采用营养液栽培,以葫芦为砧木,以小型西瓜为接穗,利用SDS-PAGE凝胶电泳,研究了嫁接对50 mmol·L-1,Nacl胁迫下西瓜幼苗生长和可溶性蛋白表达的影响.结果表明:嫁接可使盐胁迫下西瓜幼苗的株高、茎粗、根长、干重、鲜重、叶面积和根系表面积显著增加,叶片可溶性蛋白含量明显提高,大量可溶性蛋白表达增强,并出现247.7x103和107.9x103两种新蛋白;而盐胁迫下自根苗各项生长指标和叶片可溶性蛋白均显著降低,可溶性蛋白表达明显减弱.随着胁迫时间的延长,至少有12种蛋白表达量发生明显变化,其相对分子质量(x103)分别为:244.7、240.0、74.2、61.2、58.1、45.0、42.0、40.1、36.4、29.1、15.7和15.5,这12种蛋白可能与嫁接提高西瓜幼苗耐盐性密切相关.     

BS-DTAB复配修饰红壤对苯酚的吸附

为了探究复配修饰后,可变电荷类型的红壤与恒电荷土壤对苯酚的吸附差异,以红壤作为供试土样,在两性表面活性剂BS-12(十二烷基二甲基甜菜碱)修饰的基础上,以阳离子型表面活性剂DTAB(十二烷基三甲基溴化铵)复配修饰制备两性-阳离子复配修饰红壤,采用批处理法研究在单一苯酚及Cd2+复合条件下供试土样对苯酚的吸附效果,并分析不同修饰比例、温度、离子强度和pH的影响。结果表明,DTAB复配修饰增强了BS-12两性修饰红壤对苯酚的吸附能力,单一苯酚表现出在总修饰比例小于150%CEC时吸附量随着修饰比例的增加而递增;各修饰土对苯酚的吸附具有增温负效应;苯酚吸附量随着pH的升高而降低;随着离子强度的增大,苯酚单一处理时供试土样对苯酚吸附量减少,但苯酚和Cd2+复合处理时,则呈现先降低后升高的趋势。Henry模型能较好地拟合各修饰红壤对苯酚吸附的等温吸附数据,吸附以分配机制为主;供试土样对苯酚的吸附属于自发的物理吸附过程。复配修饰红壤的苯酚吸附量低于恒电荷土壤,其黏土矿物成分决定的低CEC是主要影响因素。     

Beta-arrestin 2: a receptor-regulated MAPK scaffold for the activation of JNK3

beta-Arrestins, originally discovered in the context of heterotrimeric guanine nucleotide binding protein-coupled receptor (GPCR) desensitization, also function in internalization and signaling of these receptors. We identified c-Jun amino-terminal kinase 3 (JNK3) as a binding partner of beta-arrestin 2 using a yeast two-hybrid screen and by coimmunoprecipitation from mouse brain extracts or cotransfected COS-7 cells. The upstream JNK activators apoptosis signal-regulating kinase 1 (ASK1) and mitogen-activated protein kinase (MAPK) kinase 4 were also found in complex with beta-arrestin 2. Cellular transfection of beta-arrestin 2 caused cytosolic retention of JNK3 and enhanced JNK3 phosphorylation stimulated by ASK1. Moreover, stimulation of the angiotensin II type 1A receptor activated JNK3 and triggered the colocalization of beta-arrestin 2 and active JNK3 to intracellular vesicles. Thus, beta-arrestin 2 acts as a scaffold protein, which brings the spatial distribution and activity of this MAPK module under the control of a GPCR.     

Recognition of thymine adenine.base pairs by guanine in a pyrimidine triple helix motif

Oligonucleotide recognition offers a powerful chemical approach for the sequence-specific binding of double-helical DNA. In the pyrimidine-Hoogsteen model, a binding size of greater than 15 homopurine base pairs affords greater than 30 discrete sequence-specific hydrogen bonds to duplex DNA. Because pyrimidine oligonucleotides limit triple helix formation to homopurine tracts, it is desirable to determine whether oligonucleotides can be used to bind all four base pairs of DNA. A general solution would allow targeting of oligonucleotides (or their analogs) to any given sequence in the human genome. A study of 20 base triplets reveals that the triple helix can be extended from homopurine to mixed sequences. Guanine contained within a pyrimidine oligonucleotide specifically recognizes thymine.adenine base pairs in duplex DNA. Such specificity allows binding at mixed sites in DNA from simian virus 40 and human immunodeficiency virus.     

蔬菜嫁接机器人砧、穗木套管式接合装置的设计

针对蔬菜自动嫁接时砧木和穗木的接合采用嫁接夹固定而存在的送夹装置设备复杂、耗材成本高等问题，设计了套管式接合装置。该装置由套管自动进给切断机构和套管夹持手爪组成：套管自动进给切断机构实现套管的自动进给和自动剪切。套管夹持手爪是左右对称的四杆机构，左右各有1个主动杆和从动杆。手爪执行构件固定在从动杆上；套管夹持手爪可将套管在开口处撑开，实现套管的张开和闭合。建立了套管式接合装置的数学模型，对夹持手爪的设计参数的优化结果为：当主、从动杆长度为35和25mm，手爪执行构件长度为15mm、手爪两转轴间距为6mm、力作用点与转轴连线的距离为21mm、电磁铁行程为5mm时，套管张1：7幅度为5．4mm。样机试验结果表明，套管夹持手爪将套管套在砧、穗木接合处的成功率为97％，达到设计要求。     

嫩枝腹接夏蜡梅

原始珍稀植物——中国夏蜡梅,被列为我国二级保护植物。为保护夏蜡梅,本文介绍了用蜡梅作砧木,采用夏蜡梅为接穗,以"嫩枝腹接"的方法,成功嫁接成活夏蜡梅,并用文字及图解的方法,讲述了"嫩枝腹接"的方法及步骤。