我们感谢博士博士迈克尔卡舍尔（，贝塞斯达，MA，美国国家卫生研究院）向我们发送菌株，质粒和必要的协议。我们感谢SpecraMax酶标仪约翰格洛弗（博士，加拿大多伦多大学生物化学系）。英国是一个国家科学与工程研究理事会，加拿大（NSERC）的研究生奖学金，加拿大在与疾病相关的膜蛋白的结构生物学研究所的卫生研究战略培训计划，及多伦多大学打开奖学金获得者。这项工作是支持由授予的加拿大卫生研究院（澳门币67210）往华。

1）试剂和仪器<ol><li>首先，准备以下三种解决方案：1 mL的溶液A，它是由L -赖氨酸8毫米，100毫米的钠2 - （N -吗啉）ethanesulphonic酸（MES），pH值6.5，0.2毫米核苷酸，核苷酸无论是：鸟苷二磷酸总值（GDP），三磷酸鸟苷（GTP），5&#39; -鸟苷二磷酸，3&#39; -二磷酸果糖（ppGpp），或5&#39; -鸟苷三磷酸，3&#39; -二磷酸（pppGpp），0.1毫米哆5&#39; -磷酸（PLP），1毫米β-巯基乙醇/（β- ME）。 1毫升溶液B，包括100毫米钠MES的pH值6.5，0.1毫米工党，1毫米的β- ME公司和50 nm LdcI。 LdcI纯化斯奈德等 6和Kanjee 等 。14。 1毫升溶液C溶液B相同，但不包含LdcI。 </li><li>准备100毫升的一站式解决方案，为每孔96孔聚苯乙烯板，使用多道移液器1米碳酸钠（10.6 g/100毫升）和分装50μL的组成。加入30μL水盘，然后覆盖。注意增加水量的总和，并在酶反应中提取的样本量必须等于50微升。在这种情况下，20μL酶反应样品将被删除。 </li><li> 4706μL水，包裹在铝箔稀释294μL5％（W / V）TNBS股票准备在10毫米的TNBS溶液5毫升，并保持在冰上。 </li><li>平衡的Eppendorf恒温器加在37 ° C恒温器加在6列有24个井。原理图参见图2。标签1.5 mL的Eppendorf管中表示，将被测试（每列）的核苷酸的身份：GTP（列A），国内生产总值（B列），ppGpp（C列），pppGpp（D列），没有核苷酸（E列）和蛋白质样品（F列）。 </li><li>机架几箱200μL，提示等，每个交替行省略总给人一种四排提示。这是在酶的检测与温控器加heatblock使用多道移液器必要。 </li><li>平衡数字Heatblock（VWR）在42 ° C。 </li><li>将上冰96孔2.0 mL聚丙烯板冷却。 </li></ol> 2）LdcI含量<ol><li>分装50μL溶液1.5毫升的Eppendorf管中的Eppendorf恒温5列每个相应的核苷酸。 </li><li>加入330μL溶液B三个F列管，并添加330μL溶液C（无控制蛋白质的）列F中的最后管</li><li>平衡的解决方案，在37 ° C的五分钟。提示：5分钟后，切断在加热块中心的管帽，以防止他们干扰下一步要使用的多道移液器的。 </li><li>从F列管到每个曝光在列管使用一个5-50微升VWR多通道移液器，转让50微升。管头混合尽快启动定时器。 </li><li> 2，4和6分钟，取出20μL的样品使用多道移液器和一站式解决方案。 </li><li>注：一站式解决方案的样品可以覆盖保鲜膜，并冻结在-20 ° C进行后续处理。板应与TNBS反应前在室温下解冻。 </li></ol> 3）TNBS反应和颜色开发<ol><li>加入50μL10 mM的TNBS解决方案的一站式解决方案，使用多通道移液器，然后孵育42 ° C 6分钟。该解决方案将变成一个暗黄色/橙色作为TNBS与赖氨酸和尸胺反应。 </li><li> 6分钟后，在冰上冷却板减慢反应。 </li><li>取出100μL的样品使用一个VWR 20-200μL多通道移液器和地点，在2毫升深孔板在冰上冷却。转让冰水桶的通风柜。 </li><li>添加500μL，每口井使用HandyStep（品牌）重复移液器和12.5毫升枪头（Plastibrand）的甲苯。 </li><li>擦去多余的甲苯，使用一个kimwipe和罩板包装胶带条。确保稳固地向下按压，取得了良好的密封。与平盖盖96孔板，然后大力握手为1分30秒。 </li><li>离开的解决方案，以解决5分钟。 TNP -尸现在是在上层的甲苯阶段，而TNP -赖氨酸仍然溶于水（见图1）。 </li><li>取出200μL甲苯20-200μL多道移液器使用到96孔板为阅读。注意：确保检查被删除每个样品是明确的，没有任何底部的水相。注意：使用屏障的提示，以防止甲苯多通道移液器损坏。 </li><li>阅读在SpectraMax 340酶标仪在340 nm处的吸光度。 </li><li>要干净的石英石板材，冲洗出来的甲苯与水，并放置在一个大的石英石板材通风柜的玻璃托盘。倒入100毫升的70％（V / V）硝酸的7:3的混合物：95％（V / V）乙醇，涵盖了第二个玻璃托盘的石英石板材。警告：反应是高度放热反应，有时爆炸穿适当的保护，并确保通风柜绦设置为低6“级，冷却后，用清水洗出硝酸，然后95％的乙醇。 </li></ol> 4）代表性的成果 1）尸标准曲线（图3） 检测是描述没有任何L -赖氨酸或LdcI，但和不同浓度的尸，而不是被用来凭经验判断检测的线性范围。该法线性0.25外径340，对应〜22 nmoles尸（图3）。 2）活动的LdcI（图4） LdcI单独的活动被确定为153.5（± 18.1）nmoles尸min - 1的LdcI在pH值6.5 - 1微克。 LdcI活动是在100微米GTP或GDP的存在的影响，但强烈的抑制作用pppGpp和ppGpp（图4）的存在（&gt; 10倍）。 <img src="/files/ftp_upload/2094/2094fig1.jpg" alt="图1" /> 图1。 L -赖氨酸的LdcI反应示意图。脱羧反应生成CO 2和尸，以及随后在高pH值TNBS反应生成N，N - bistrinitrophenylcadaverine（TNP -尸）和N， N “bistrinitrophenyllysine（TNP -赖氨酸）。基于藩等al.11 <img src="/files/ftp_upload/2094/2094fig2.jpg" alt="图2" /> 图2。 Eppendorf公司温控器的安装 。布局在24孔的Eppendorf恒温样品检测步骤的描述（黑体表示）。箭头指示的反应，根据该协议解决方案的转移。也表示去除反应液在96孔板的一站式解决方案。 <img src="/files/ftp_upload/2094/2094fig3.jpg" alt="图3" /> 图3。尸标准曲线的吸光度在340纳米，与尸nmoles情节所示。误差棒代表至少有三个独立的测量的标准偏差。最佳拟合线也显示，有一个R2为0.996。 <img src="/files/ftp_upload/2094/2094fig4.jpg" alt="图4" /> 图4。 LdcI检测结果。情节LdcI活动率（nmoles尸制作1分钟1微克LdcI）pppGpp，ppGpp 100μM的GTP，GDP和核苷酸的情况下显示。严格的响应核苷酸（P）ppGpp能显着抑制LdcI活动。误差棒代表至少6个独立的测量的标准偏差。

<ol>
	<li>Gale, E. F., Epps, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+the+pH+of+the+medium+during+growth+on+the+enzymic+activities+of+bacteria+(Escherichia+coli+and+Micrococcus+lysodeikticus)+and+the+biological+significance+of+the+changes+produced.">The effect of the pH of the medium during growth on the enzymic activities of bacteria (Escherichia coli and Micrococcus lysodeikticus) and the biological significance of the changes produced.</a> Biochem J. 36, 600-618 (1942).</li><li>Foster, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Escherichia+coli+acid+resistance:+tales+of+an+amateur+acidophile.">Escherichia coli acid resistance: tales of an amateur acidophile.</a> Nat Rev Microbiol. 2, 898-907 (2004).</li><li>Castanie-Cornet, M. P., Penfound, T. A., Smith, D., Elliott, J. 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赖氨酸脱羧酶试验，TNBS是L -赖氨酸和尸伯胺反应形成，TNP -赖氨酸和TNP -尸加合物（图1）。由于TNP -赖氨酸的羧酸基团的存在，这种加合物仍然易溶于水，而TNP -尸，缺乏羧酸 ，甲苯11分区。其他类型羧酸组的损失发生在反应过程中的氨基酸，可以更广泛地利用这类型的检测。这发生在L -鸟氨酸诱导鸟氨酸脱羧酶SPEF的脱羧形成多胺腐胺和L -精氨酸脱羧诱导精氨酸脱羧酶ADIA形成多胺胍丁...

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		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
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<tr>
<td>2,4,6-trinitrobenzensulfonic acid </td>
<td>&nbsp;</td>
<td>Sigma Aldrich</td>
<td>P2297</td>
<td>&nbsp;</td>
<tr>
<td>0.1 mM pyridoxal 5'-phosphate (PLP)</td>
<td>&nbsp;</td>
<td>Sigma Aldrich</td>
<td>P9255</td>
<td>&nbsp;</td>
<tr>
<td>Cadaverine</td>
<td>&nbsp;</td>
<td>Sigma Aldrich</td>
<td>D22606</td>
<td>&nbsp;</td>
<tr>
<td>96 well polystyrene plates</td>
<td>&nbsp;</td>
<td>Sarstedt</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>96-well quartz plate</td>
<td>&nbsp;</td>
<td>Hellma</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>VWR Digital Heatblock</td>
<td>&nbsp;</td>
<td>VWR</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>ThermoStat Plus</td>
<td>&nbsp;</td>
<td>Eppendorf</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
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<td>2.0 mL 96-well polypropylene plates</td>
<td>&nbsp;</td>
<td>Axygen</td>
<td>P-DW-20-C</td>
<td>&nbsp;</td>
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<td>Handy Step Repeat Pipettor</td>
<td>&nbsp;</td>
<td>Brand</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>12.5 mL Repeat Pipettor Tips</td>
<td>&nbsp;</td>
<td>Brand (Plastibrand)</td>
<td>702378</td>
<td>&nbsp;</td>
<tr>
<td>SpectraMax 340PC Plate Reader</td>
<td>&nbsp;</td>
<td>SpectraMax</td>
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an assay for measuring the activity of escherichia coli inducible lysine decarboxyase

大肠杆菌是肠道细菌能够较广泛的pH值（pH值5 - 9）增长1的，令人难以置信的，是能够生存的极端酸强调，通过哺乳动物的胃pH值下降，包括通过低作为pH值1 - 2 2。为了使这样一个广泛偏酸生存，E.大肠杆菌拥有四种不同的诱导氨基酸decarboxylases decarboxylate基板在质子依赖性氨基酸，从而提高内部的pH值。 decarboxylases包括谷氨酸decarboxylases嘎达和GadB 3，精氨酸脱羧酶ADIA 4，赖氨酸脱羧酶LdcI 5，6和7鸟氨酸脱羧酶SPEF。所有这些酶的利用吡哆醛-5 -磷酸作为共同因子8，函数内的膜基板产品逆向转运，删除脱羧产品在外部介质换取新鲜的基板2。在LdcI的情况下，赖氨酸尸逆向转运蛋白被称为农发行。最近，我们确定了X射线晶体结构的LdcI 2.0 A，我们发现了一个新的小分子绑定到LdcI严格的反应调节鸟苷5&#39; -二磷酸，3&#39; -二磷酸果糖（ppGpp）14 。严格的反应时，会发生细胞急剧增长的经验营养剥夺或其他9讲。因此，细胞产生ppGpp导致信号级联，最终从指数的增长转移到固定相增长10。我们已经证明，ppGpp是LdcI 14特异性抑制剂。在这里，我们描述赖氨酸脱羧酶检测，修改从藩等人开发的的实验。11，我们用于确定LdcI活动pppGpp / ppGpp该活动的影响。 LdcI脱羧反应，消除了L -赖氨酸的α-羧基组和产生的二氧化碳和尸胺（1,5 - diaminopentane） 5。 L -赖氨酸和尸，可在高pH值2,4,6 trinitrobenzensulfonic酸（TNBS）反应生成N，N - bistrinitrophenylcadaverine（TNP -尸）和N，N&#39; - bistrinitrophenyllysine（TNP -赖氨酸），分别11。 TNP -尸可以分开，前者是可溶于有机溶剂，如甲苯，而后者则没有（见图1），TNP -赖氨酸。检测的线性范围为使用纯化尸凭经验确定。

Watch this Scientific Journal Video about An Assay for Measuring the Activity of Escherichia coli Inducible Lysine Decarboxyase at JoVE.com

An Assay for Measuring the Activity of Escherichia coli Inducible Lysine Decarboxyase

2,4,6 - trinitrobenzensulfonic酸反应的底物L -赖氨酸和产品尸形成加合物在甲苯的溶解度差，诱导赖氨酸脱羧酶的活动都受到监控。

用于测量的活性测定大肠埃希氏菌诱导赖氨酸Decarboxyase

Escherichia coli is an enteric bacterium that is capable of growing over a wide range of pH values (pH 5 - 9)1 and, incredibly, is able to survive extreme ...

an-assay-for-measuring-activity-escherichia-coli-inducible-lysine

Research

JoVE Journal

Biology

An Assay for Measuring the Activity of Escherichia coli Inducible Lysine Decarboxyase

14.1K 次观看.  University of Toronto. 2,4,6 - trinitrobenzensulfonic酸反应的底物L -赖氨酸和产品尸形成加合物在甲苯的溶解度差，诱导赖氨酸脱羧酶的活动都受到监控。

视频: An Assay for Measuring the Activity of Escherichia coli Inducible Lysine Decarboxyase

Measuring the Bending Stiffness of Bacterial Cells Using an Optical Trap

We developed a protocol to measure the bending rigidity of filamentous rod-shaped bacteria. Forces are applied with an optical trap, a microscopic three-dimensional spring made of light that is formed when a high-intensity laser beam is focused to a very small spot by a microscope's objective lens. To bend a cell, we first bind live bacteria to a chemically-treated coverslip. As these cells grow, the middle of the cells remains bound to the coverslip but the growing ends are free of this restraint. By inducing filamentous growth with the drug cephalexin, we are able to identify cells in which one end of the cell was stuck to the surface while the other end remained unattached and susceptible to bending forces. A bending force is then applied with an optical trap by binding a polylysine-coated bead to the tip of a growing cell. Both the force and the displacement of the bead are recorded and the bending stiffness of the cell is the slope of this relationship.

We present a protocol for bending filamentous bacterial cells attached to a cover-slip surface with an optical trap to measure the cellular bending stiffness.

测量细菌细胞的抗弯刚度，使用光学陷阱

We developed a protocol to measure the bending rigidity of filamentous rod-shaped bacteria. Forces are applied with an optical trap, a microscopic ...

科研

生物学

High Throughput Screening of Fungal Endoglucanase Activity in Escherichia coli

Cellulase enzymes (endoglucanases, cellobiohydrolases, and &beta;-glucosidases) hydrolyze cellulose into component sugars, which in turn can be converted into fuel alcohols1. The potential for enzymatic hydrolysis of cellulosic biomass to provide renewable energy has intensified efforts to engineer cellulases for economical fuel production2. Of particular interest are fungal cellulases3-8, which are already being used industrially for foods and textiles processing.
Identifying active variants among a library of mutant cellulases is critical to the engineering process; active mutants can be further tested for improved properties and/or subjected to additional mutagenesis. Efficient engineering of fungal cellulases has been hampered by a lack of genetic tools for native organisms and by difficulties in expressing the enzymes in heterologous hosts. Recently, Morikawa and coworkers developed a method for expressing in E. coli the catalytic domains of endoglucanases from H. jecorina3,9, an important industrial fungus with the capacity to secrete cellulases in large quantities. Functional E. coli expression has also been reported for cellulases from other fungi, including Macrophomina phaseolina10 and Phanerochaete chrysosporium11-12. 
We present a method for high throughput screening of fungal endoglucanase activity in E. coli. (Fig 1) This method uses the common microbial dye Congo Red (CR) to visualize enzymatic degradation of carboxymethyl cellulose (CMC) by cells growing on solid medium. The activity assay requires inexpensive reagents, minimal manipulation, and gives unambiguous results as zones of degradation (&#x201C;halos&#x201D;) at the colony site. Although a quantitative measure of enzymatic activity cannot be determined by this method, we have found that halo size correlates with total enzymatic activity in the cell. Further characterization of individual positive clones will determine , relative protein fitness. 
Traditional bacterial whole cell CMC/CR activity assays13 involve pouring agar containing CMC onto colonies, which is subject to cross-contamination, or incubating cultures in CMC agar wells, which is less amenable to large-scale experimentation. Here we report an improved protocol that modifies existing wash methods14 for cellulase activity: cells grown on CMC agar plates are removed prior to CR staining. Our protocol significantly reduces cross-contamination and is highly scalable, allowing the rapid screening of thousands of clones. In addition to H. jecorina enzymes, we have expressed and screened endoglucanase variants from the Thermoascus aurantiacus and Penicillium decumbens (shown in Figure 2), suggesting that this protocol is applicable to enzymes from a range of organisms.

High Throughput Screening of Fungal Endoglucanase Activity in Escherichia coli

We describe a low cost, high throughput method to screen for fungal endoglucanase activity in E. coli. The method relies on a simple visual readout of substrate degradation, does not require enzyme purification, and is highly scalable. This allows for the rapid screening of large libraries of enzyme variants.

真菌内切葡聚糖酶的活性高通量筛选大肠埃希氏菌</em

Cellulase enzymes (endoglucanases, cellobiohydrolases, and &beta;-glucosidases) hydrolyze cellulose into component sugars, which in turn can be converted ...

Application of MassSQUIRM for Quantitative Measurements of Lysine Demethylase Activity

Recently, epigenetic regulators have been discovered as key players in many different diseases 1-3. As a result, these enzymes are prime targets for small molecule studies and drug development 4. Many epigenetic regulators have only recently been discovered and are still in the process of being classified. Among these enzymes are lysine demethylases which remove methyl groups from lysines on histones and other proteins. Due to the novel nature of this class of enzymes, few assays have been developed to study their activity. This has been a road block to both the classification and high throughput study of histone demethylases. Currently, very few demethylase assays exist. Those that do exist tend to be qualitative in nature and cannot simultaneously discern between the different lysine methylation states (un-, mono-, di- and tri-). Mass spectrometry is commonly used to determine demethylase activity but current mass spectrometric assays do not address whether differentially methylated peptides ionize differently. Differential ionization of methylated peptides makes comparing methylation states difficult and certainly not quantitative (Figure 1A). Thus available assays are not optimized for the comprehensive analysis of demethylase activity.
Here we describe a method called MassSQUIRM (mass spectrometric quantitation using isotopic reductive methylation) that is based on reductive methylation of amine groups with deuterated formaldehyde to force all lysines to be di-methylated, thus making them essentially the same chemical species and therefore ionize the same (Figure 1B). The only chemical difference following the reductive methylation is hydrogen and deuterium, which does not affect MALDI ionization efficiencies. The MassSQUIRM assay is specific for demethylase reaction products with un-, mono- or di-methylated lysines. The assay is also applicable to lysine methyltransferases giving the same reaction products. Here, we use a combination of reductive methylation chemistry and MALDI mass spectrometry to measure the activity of LSD1, a lysine demethylase capable of removing di- and mono-methyl groups, on a synthetic peptide substrate 5. This assay is simple and easily amenable to any lab with access to a MALDI mass spectrometer in lab or through a proteomics facility. The assay has ~8-fold dynamic range and is readily scalable to plate format 5.

We present a method for using MALDI mass spectrometry and reductive methylation chemistry to quantify changes in lysine methylation.

赖氨酸去甲基化酶活性的定量测量中的应用的MassSQUIRM

Recently, epigenetic regulators have been discovered as key players in many different diseases 1-3. As a result, these enzymes are prime targets for small ...

Rapid Protocol for Preparation of Electrocompetent Escherichia coli and Vibrio cholerae

Electroporation has become a widely used method for rapidly and efficiently introducing foreign DNA into a wide range of cells. Electrotransformation has become the method of choice for introducing DNA into prokaryotes that are not naturally competent. Electroporation is a rapid, efficient, and streamlined transformation method that, in addition to purified DNA and competent bacteria, requires commercially available gene pulse controller and cuvettes. In contrast to the pulsing step, preparation of electrocompetent cells is time consuming and labor intensive involving repeated rounds of centrifugation and washes in decreasing volumes of sterile, cold water, or non-ionic buffers of large volumes of cultures grown to mid-logarithmic phase of growth. Time and effort can be saved by purchasing electrocompetent cells from commercial sources, but the selection is limited to commonly employed E. coli laboratory strains. We are hereby disseminating a rapid and efficient method for preparing electrocompetent E. coli, which has been in use by bacteriology laboratories for some time, can be adapted to V. cholerae and other prokaryotes. While we cannot ascertain whom to credit for developing the original technique, we are hereby making it available to the scientific community.

Rapid Protocol for Preparation of Electrocompetent Escherichia coli and Vibrio cholerae

Electroporation is a commonly employed method for introducing DNA into bacteria in a process known as transformation. Traditional protocols for the preparation of electrocompetent cells are time consuming and labor intensive. This article describes an alternate, rapid, and efficient method for the preparation of electrocompetent cells presently employed by some laboratories.

对于电感受的制备快速协议<em&gt;大肠杆菌</em&gt;和<em&gt;霍乱弧菌</em

Electroporation has become a widely used method for rapidly and efficiently introducing foreign DNA into a wide range of cells. Electrotransformation has ...

Protocols for Implementing an Escherichia coli Based TX-TL Cell-Free Expression System for Synthetic Biology

Ideal cell-free expression systems can theoretically emulate an in vivo cellular environment in a controlled in vitro platform.1 This is useful for expressing proteins and genetic circuits in a controlled manner as well as for providing a prototyping environment for synthetic biology.2,3 To achieve the latter goal, cell-free expression systems that preserve endogenous Escherichia coli transcription-translation mechanisms are able to more accurately reflect in vivo cellular dynamics than those based on T7 RNA polymerase transcription. We describe the preparation and execution of an efficient endogenous E. coli based transcription-translation (TX-TL) cell-free expression system that can produce equivalent amounts of protein as T7-based systems at a 98% cost reduction to similar commercial systems.4,5 The preparation of buffers and crude cell extract are described, as well as the execution of a three tube TX-TL reaction. The entire protocol takes five days to prepare and yields enough material for up to 3000 single reactions in one preparation. Once prepared, each reaction takes under 8 hr from setup to data collection and analysis. Mechanisms of regulation and transcription exogenous to E. coli, such as lac/tet repressors and T7 RNA polymerase, can be supplemented.6 Endogenous properties, such as mRNA and DNA degradation rates, can also be adjusted.7 The TX-TL cell-free expression system has been demonstrated for large-scale circuit assembly, exploring biological phenomena, and expression of proteins under both T7- and endogenous promoters.6,8 Accompanying mathematical models are available.9,10 The resulting system has unique applications in synthetic biology as a prototyping environment, or "TX-TL biomolecular breadboard."

Protocols for Implementing an Escherichia coli Based TX-TL Cell-Free Expression System for Synthetic Biology

This five-day protocol outlines all steps, equipment, and supplemental software necessary for creating and running an efficient endogenous Escherichia coli based TX-TL cell-free expression system from scratch. With reagents, the protocol takes 8 hours or less to setup a reaction, collect, and process data.

协议用于实现<em&gt;大肠杆菌</em&gt;基于TX-TL无细胞表达系统合成生物学

Ideal cell-free expression systems can theoretically emulate an in vivo cellular environment in a controlled in vitro platform.1 This is useful for ...

Detection of Live Escherichia coli O157:H7 Cells by PMA-qPCR

A unique open reading frame (ORF) Z3276 was identified as a specific genetic marker for E. coli O157:H7. A qPCR assay was developed for detection of E. coli O157:H7 by targeting ORF Z3276. With this assay, we can detect as low as a few copies of the genome of DNA of E. coli O157:H7. The sensitivity and specificity of the assay were confirmed by intensive validation tests with a large number of E. coli O157:H7 strains (n = 369) and non-O157 strains (n = 112). Furthermore, we have combined propidium monoazide (PMA) procedure with the newly developed qPCR protocol for selective detection of live cells from dead cells. Amplification of DNA from PMA-treated dead cells was almost completely inhibited in contrast to virtually unaffected amplification of DNA from PMA-treated live cells. Additionally, the protocol has been modified and adapted to a 96-well plate format for an easy and consistent handling of a large number of samples. This method is expected to have an impact on accurate microbiological and epidemiological monitoring of food safety and environmental source.

Detection of Live Escherichia coli O157:H7 Cells by PMA-qPCR

A qPCR assay was developed for detection of Escherichia coli O157:H7 targeting a unique genetic marker, Z3276. The qPCR was combined with propidium monoazide (PMA) treatment for live cell detection. This protocol has been modified and adapted to a 96-well plate format for easy and consistent handling of numerous samples

检测现场的<em&gt;大肠杆菌</em&gt; O157：H7细胞的PMA-qPCR的

A unique open reading frame (ORF) Z3276 was identified as a specific genetic marker for E. coli O157:H7. A qPCR assay was developed for detection of E. ...

Green Fluorescent Protein-based Expression Screening of Membrane Proteins in Escherichia coli

The production of recombinant membrane proteins for structural and functional studies remains technically challenging due to low levels of expression and the inherent instability of many membrane proteins once solubilized in detergents. A protocol is described that combines ligation independent cloning of membrane proteins as GFP fusions with expression in Escherichia coli detected by GFP fluorescence. This enables the construction and expression screening of multiple membrane protein/variants to identify candidates suitable for further investment of time and effort. The GFP reporter is used in a primary screen of expression by visualizing GFP fluorescence following SDS polyacrylamide gel electrophoresis (SDS-PAGE). Membrane proteins that show both a high expression level with minimum degradation as indicated by the absence of free GFP, are selected for a secondary screen. These constructs are scaled and a total membrane fraction prepared and solubilized in four different detergents. Following ultracentrifugation to remove detergent-insoluble material, lysates are analyzed by fluorescence detection size exclusion chromatography (FSEC). Monitoring the size exclusion profile by GFP fluorescence provides information about the mono-dispersity and integrity of the membrane proteins in different detergents. Protein: detergent combinations that elute with a symmetrical peak with little or no free GFP and minimum aggregation are candidates for subsequent purification. Using the above methodology, the heterologous expression in E. coli of SED (shape, elongation, division, and sporulation) proteins from 47 different species of bacteria was analyzed. These proteins typically have ten transmembrane domains and are essential for cell division. The results show that the production of the SEDs orthologues in E. coli was highly variable with respect to the expression levels and integrity of the GFP fusion proteins. The experiment identified a subset for further investigation.

Green Fluorescent Protein-based Expression Screening of Membrane Proteins in Escherichia coli

A streamlined approach to screening for the expression of recombinant membrane proteins in Escherichia coli based on fusion to green fluorescent protein is presented.

膜蛋白的绿色荧光蛋白为基础的表达筛选<em&gt;大肠杆菌</em

The production of recombinant membrane proteins for structural and functional studies remains technically challenging due to low levels of expression and ...

The Multifaceted Benefits of Protein Co-expression in Escherichia coli

We report here that the expression of protein complexes in vivo in Escherichia coli can be more convenient than traditional reconstitution experiments in vitro. In particular, we show that the poor solubility of Escherichia coli DNA polymerase III &#949; subunit (featuring 3&#8217;-5&#8217; exonuclease activity) is highly improved when the same protein is co-expressed with the &#945; and &#952; subunits (featuring DNA polymerase activity and stabilizing &#949;, respectively). We also show that protein co-expression in E. coli can be used to efficiently test the competence of subunits from different bacterial species to associate in a functional protein complex. We indeed show that the &#945; subunit of Deinococcus radiodurans DNA polymerase III can be co-expressed in vivo with the &#949; subunit of E. coli. In addition, we report on the use of protein co-expression to modulate mutation frequency in E. coli. By expressing the wild-type &#949; subunit under the control of the araBAD promoter (arabinose-inducible), and co-expressing the mutagenic D12A variant of the same protein, under the control of the lac promoter (inducible by isopropyl-thio-&#946;-D-galactopyranoside, IPTG), we were able to alter the E. coli mutation frequency using appropriate concentrations of the inducers arabinose and IPTG. Finally, we discuss recent advances and future challenges of protein co-expression in E. coli.

The Multifaceted Benefits of Protein Co-expression in Escherichia coli

Protein co-expression is a powerful alternative to the reconstitution in vitro of protein complexes, and is of help in performing biochemical and genetic tests in vivo. Here we report on the use of protein co-expression in Escherichia coli to obtain protein complexes, and to tune the mutation frequency of cells.

蛋白质的共表达了多方面的好处<em&gt;大肠杆菌</em

We report here that the expression of protein complexes in vivo in Escherichia coli can be more convenient than traditional reconstitution experiments in ...

Residue-specific Incorporation of Noncanonical Amino Acids into Model Proteins Using an Escherichia coli Cell-free Transcription-translation System

The canonical set of amino acids leads to an exceptionally wide range of protein functionality. Nevertheless, the set of residues still imposes limitations on potential protein applications. The incorporation of noncanonical amino acids can enlarge this scope. There are two complementary approaches for the incorporation of noncanonical amino acids. For site-specific incorporation, in addition to the endogenous canonical translational machineries, an orthogonal aminoacyl-tRNA-synthetase-tRNA pair must be provided that does not interact with the canonical ones. Consequently, a codon that is not assigned to a canonical amino acid, usually a stop codon, is also required. This genetic code expansion enables the incorporation of a noncanonical amino acid at a single, given site within the protein. The here presented work describes residue-specific incorporation where the genetic code is reassigned within the endogenous translational system. The translation machinery accepts the noncanonical amino acid as a surrogate to incorporate it at canonically prescribed locations, i.e., all occurrences of a canonical amino acid in the protein are replaced by the noncanonical one. The incorporation of noncanonical amino acids can change the protein structure, causing considerably modified physical and chemical properties. Noncanonical amino acid analogs often act as cell growth inhibitors for expression hosts since they modify endogenous proteins, limiting in vivo protein production. In vivo incorporation of toxic noncanonical amino acids into proteins remains particularly challenging. Here, a cell-free approach for a complete replacement of L-arginine by the noncanonical amino acid L-canavanine is presented. It circumvents the inherent difficulties of in vivo expression. Additionally, a protocol to prepare target proteins for mass spectral analysis is included. It is shown that L-lysine can be replaced by L-hydroxy-lysine, albeit with lower efficiency. In principle, any noncanonical amino acid analog can be incorporated using the presented method as long as the endogenous in vitro translation system recognizes it.

Residue-specific Incorporation of Noncanonical Amino Acids into Model Proteins Using an Escherichia coli Cell-free Transcription-translation System

An easy-to-use, cell-free expression protocol for the residue-specific incorporation of noncanonical amino acid analogs into proteins, including downstream analysis, is presented for medical, pharmaceutic, structural and functional studies.

非经典氨基酸的具体残留纳入到模型蛋白质使用<em&gt;大肠杆菌</em&gt;无细胞转录翻译系统

The canonical set of amino acids leads to an exceptionally wide range of protein functionality. Nevertheless, the set of residues still imposes ...

Measuring Lactase Enzymatic Activity in the Teaching Lab

Understanding how enzymes work, and relating this to real life examples, is critical to a wide range of undergraduate degrees in the biological and biomedical sciences. This easy to follow protocol was developed for first year undergraduate pharmacy students and provides an entry-level introduction to enzyme reactions and analytical procedures for enzyme analysis. The enzyme of choice is lactase, as this represents an example of a commercially available enzyme relevant to human disease/pharmaceutical practice. Lactase is extracted from dietary supplement tablets, and assessed using a colorimetric assay based upon hydrolysis of an artificial substrate for lactase (ortho-nitrophenol-beta-D-galactopyranoside, ONPG). Release of ortho-nitrophenol following the hydrolytic cleavage of ONPG by lactase is measured by a change in absorbance at 420 nm, and the effect of the temperature on the enzymatic reaction is evaluated by carrying out the reaction on ice, at room temperature and at 37 &#176;C. More advanced analysis can be implemented using this protocol by assessing the enzyme activity under different conditions and using different reagents.

The enzymatic activity of lactase is essential for the catabolic processing of the disaccharide lactose. Here, the activity of lactase found in dietary supplements is assayed using a colorimetric assay. This provides students with an experimental platform for understanding the activity of lactase and enzyme kinetics.

实验教学中乳糖酶活性的测定

Understanding how enzymes work, and relating this to real life examples, is critical to a wide range of undergraduate degrees in the biological and ...