这项研究已经由西蒙·弗雷泽大学的启动资金支持。

1，嘉实膜<ol><li>添加低渗缓冲液（10mM的Tris-HCl，10mM的氯化钾，1.5毫摩尔MgCl 2，pH 8.0）中与蛋白酶抑制剂混合物到细胞沉淀（〜10 8个细胞），并培育在冰上15-30分钟。裂解细胞通过使样品通过注射器针头（5-10遍），或通过一个Dounce匀浆（15-30冲程）破碎样品。使用血细胞计数器和台盼蓝染色来检查裂解的效率。 </li><li>由裂解物的差速离心获得的微粒体部分在3000 GX 15分钟，然后在100,000 GX 2小时。第一离心分离得到的颗粒，它是细胞核部分，以及上清液的离心分离后产生一个第二沉淀，它是一个包含质膜以及膜结合细胞器8的微粒体部分。最后的上层清液是胞质部分。存储的微粒体部分在-80℃冷冻进一步analys是如下所示。 </li></ol> 2，溶解，变性和精华膜蛋白<ol><li>溶解的微粒体部分中的变性缓冲液（40毫摩尔Tris，10mM的EDTA，10mM的TCEP，0.5％品RapiGest，pH8）中，然后孵育溶液，在100℃持续10分钟。 </li><li>冷却该溶液加热至室温，加入超高纯度尿素粉末在溶液中，以800万的最终浓度和孵育的样品在37℃下30分钟。 </li><li>添加碘乙酰胺储备溶液至样品以15mM的终浓度，并孵育在黑暗中的溶液30分钟，在室温下烷基化的游离硫醇的样品中。添加的DTT储液的样品，以10 mM的终浓度，并孵育另外10分钟，将溶液在室温下以淬灭过量的碘乙酰胺。 </li><li>稀释所得到的溶液用10倍的40mM Tris缓冲液在pH为8，并随后添加胰蛋白酶到样品以1:20的比例trypsi的n到总蛋白。保持在37℃的烘箱中过夜消化反应，以确保反应完成。 </li><li>通过酸化样品溶液至pH为1，用HCl，这种情况也发生故障的洗涤剂， 即品RapiGest终止消化。降解品RapiGest在37℃下反应1小时，并通过离心分离除去沉淀开发。 </li><li>清洗包含样品的肽通过C-18固相萃取（SPE）柱并通过Speed​​Vac中干燥所得到的样品上清液。 </li><li>之前和胰蛋白酶消化，以确认消化效率后执行样本的SDS-PAGE分析。 </li></ol> 3，糖肽捕获<ol><li>溶解于偶联缓冲液（100mM乙酸钠，pH 5.5）清洗过的肽。添加高碘酸钠成在10mM的最终浓度为在黑暗中30分钟，在室温下将肽溶液。这会氧化的糖链的顺式二醇基团为醛，这让聚糖对夫妇通过酰肼化学树脂。由亚硫酸钠淬灭过量的高碘酸盐在20mM的最终浓度和pH为5，在室温下10分钟。 </li><li>引入肼衍生的树脂成以1:4（树脂溶液），以一对糖肽与树脂的比率的肽溶液。在37℃下与终端到终端的旋转完全偶合反应1-2天。 </li><li>通过用1ml以下各项的洗涤树脂两次去除未结合的肽:去离子水，1.5 M氯化钠，甲醇和80％乙腈。最后，用1ml 100mM的NH 4 HCO 3洗涤树脂3次，在pH 8至系统的缓冲液交换，以100mM的NH 4 HCO 3。 <ol><li>收集上清液和洗涤的未结合的肽（可选）的分析。 </li></ol></li><li>从PNG酶F IN孵育过夜树脂释放的N-糖肽在37℃与N END到终端的旋转。通过离心和80％乙腈洗收集释放肽。干燥所得到的在Speed​​Vac中用于LC-MS分析溶液。 </li></ol> 4，进一步分馏（可选） 为了进一步简化样品的复杂性，分馏所得到的N-糖肽。例如，重新溶解干燥的肽为10毫米氨甲酸，pH值3用20％乙腈和使用强阳离子交换（SCX）色谱分级分离肽。干燥所得到的洗脱液，然后用反相LC-MS 8,17,18分析所得到的肽组分。 5，清洁释放的N-糖肽（可选） 如果关注上升为肽的潜在污染，再溶解干燥的肽为含0.1％甲酸，并使用一个MCX SPE柱，以进一步清洁肽前反相LC-MS分析。 <strong&gt;的说明:数据库搜索参数。 中的N-糖肽脱树脂的选择性裂解，PNG酶F中的N-聚糖连接的天冬酰胺转换为天冬氨酸。因此，解放区的N-糖肽的0.9840大质量转变。准确地识别这些肽，这种修改需要被添加到搜索参数一起共同修饰如蛋氨酸，半胱氨酸和氧化carbamidomethylation。

<ol>
	<li>Cho, W., Stahelin, R. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane-protein+interactions+in+cell+signaling+and+membrane+trafficking.">Membrane-protein interactions in cell signaling and membrane trafficking.</a> Annual review of biophysics and biomolecular structure. 34, 119-151 (2005).</li><li>Tadevosyan, A., Vaniotis, G., Allen, B. G., Hebert, T. E., Nattel, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=protein-coupled+receptor+signalling+in+the+cardiac+nuclear+membrane:+evidence+and+possible+roles+in+physiological+and+pathophysiological+function.">protein-coupled receptor signalling in the cardiac nuclear membrane: evidence and possible roles in physiological and pathophysiological function.</a> The Journal of physiology. 590, 1313-1330 (2012).</li><li>White, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biophysical+dissection+of+membrane+proteins.">Biophysical dissection of membrane proteins.</a> Nature. 459, 344-346 (2009).</li><li>Heijne, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane-protein+topology.+.">Membrane-protein topology. .</a> Nature reviews Molecular cell biology. 7, 909-918 (2006).</li><li>Cox, J., Mann, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+high-resolution+proteomics+for+data-driven+systems+biology.">Quantitative high-resolution proteomics for data-driven systems biology.</a> Annual review of biochemistry. 80, 273-299 (2011).</li><li>Lamond, A. I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advancing+cell+biology+through+proteomics+in+space+and+time+(PROSPECTS).">Advancing cell biology through proteomics in space and time (PROSPECTS).</a> Mol Cell Proteomics. 11, (2012).</li><li>Savas, J. N., Stein, B. D., Wu, C. C., Yates 3rd, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mass+spectrometry+accelerates+membrane+protein+analysis.">Mass spectrometry accelerates membrane protein analysis.</a> Trends in biochemical sciences. 36, 388-396 (2011).</li><li>Sun, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shotgun+glycopeptide+capture+approach+coupled+with+mass+spectrometry+for+comprehensive+glycoproteomics.">Shotgun glycopeptide capture approach coupled with mass spectrometry for comprehensive glycoproteomics.</a> Mol Cell Proteomics. 6, 141-149 (2007).</li><li>Lowe, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glycosylation,+immunity,+and+autoimmunity.">Glycosylation, immunity, and autoimmunity.</a> Cell. 104, 809-812 (2001).</li><li>Dodds, E. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gas-phase+dissociation+of+glycosylated+peptide+ions.">Gas-phase dissociation of glycosylated peptide ions.</a> Mass spectrometry reviews. 31, 666-682 (2012).</li><li>Kaji, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lectin+affinity+capture,+isotope-coded+tagging+and+mass+spectrometry+to+identify+N-linked+glycoproteins.">Lectin affinity capture, isotope-coded tagging and mass spectrometry to identify N-linked glycoproteins.</a> Nat Biotechnol. 21, 667-672 (2003).</li><li>Zhang, H., Li, X. J., Martin, D. B., Aebersold, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+quantification+of+N-linked+glycoproteins+using+hydrazide+chemistry,+stable+isotope+labeling+and+mass+spectrometry.">Identification and quantification of N-linked glycoproteins using hydrazide chemistry, stable isotope labeling and mass spectrometry.</a> Nat Biotechnol. 21, 660-666 (2003).</li><li>Hagglund, P., Bunkenborg, J., Elortza, F., Jensen, O. N., Roepstorff, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+strategy+for+identification+of+N-glycosylated+proteins+and+unambiguous+assignment+of+their+glycosylation+sites+using+HILIC+enrichment+and+partial+deglycosylation.">A new strategy for identification of N-glycosylated proteins and unambiguous assignment of their glycosylation sites using HILIC enrichment and partial deglycosylation.</a> J Proteome Res. 3, 556-566 (2004).</li><li>Bond, M. R., Kohler, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+methods+for+glycoprotein+discovery.">Chemical methods for glycoprotein discovery.</a> Current opinion in chemical biology. 11, 52-58 (2007).</li><li>Pasini, E. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In-depth+analysis+of+the+membrane+and+cytosolic+proteome+of+red+blood+cells.">In-depth analysis of the membrane and cytosolic proteome of red blood cells.</a> Blood. 108, 791-801 (2006).</li><li>Wollscheid, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mass-spectrometric+identification+and+relative+quantification+of+N-linked+cell+surface+glycoproteins.">Mass-spectrometric identification and relative quantification of N-linked cell surface glycoproteins.</a> Nat Biotechnol. 27, 378-386 (2009).</li><li>Sun, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=N-Glycoproteome+of+E14.Tg2a+mouse+embryonic+stem+cells.">N-Glycoproteome of E14.Tg2a mouse embryonic stem cells.</a> PLoS ONE. 8, (2013).</li><li>Sun, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glycocapture-assisted+global+quantitative+proteomics+(gagQP)+reveals+multiorgan+responses+in+serum+toxicoproteome.">Glycocapture-assisted global quantitative proteomics (gagQP) reveals multiorgan responses in serum toxicoproteome.</a> J Proteome Res. 12, 2034-2044 (2013).</li></ol>

作者宣称，他们有没有竞争的财务权益。

在这里，我们介绍一种糖肽捕获策略分析细胞表面蛋白。可以应用该方法来研究分泌蛋白，如血液中，以及在其他体液或细胞培养基中。 该方法的成功依赖于样本的完全消化;因此，消化效率的SDS-PAGE鉴定是必要的，尤其是对于样品的第一次分析。一个完整的消化可具有挑战性的膜蛋白，并可以仅在膜级分的彻底的溶解是可能的。当洗涤剂引入增溶过程开始和尿素的孵育后结?...

细胞表面蛋白与细胞外环境进行交互并从外部中继信号到细胞的内部。因此，这些蛋白，包括细胞外基质蛋白，在细胞生物学和生理学不等的增殖，生长，迁移，分化老化等各方面发挥关键作用。表面蛋白的功能通过与其他细胞，蛋白质和小分子1-3交互。细胞表面蛋白的分子特性是极大的兴趣不仅为生物学家也为制药公司，药品60％以上是针对细胞表面蛋白4。 串联质谱（MS），以其卓越的灵敏度，准确度和吞吐量鉴定蛋白质和多肽，一直是一个强大的工具，用于全球蛋白质组学研究5,6。然而，表面的蛋白质会对质谱为基础的蛋白质组学显著挑战，在低量的重金属修改存在最表面的蛋白质。表面蛋白的跨膜区呈现它们的疏水性;这是特别适用于多通道的跨膜蛋白的情况。因此，这是难以溶解在水溶液中的膜蛋白无洗涤剂的帮助;然而清洁剂的使用普遍抑制高效液相色谱法和质谱1,7,8的蛋白质鉴定的表现。因此，膜蛋白已被鉴定中直接LC-MS基于蛋白质组学很差。 糖基化是发生在细胞表面蛋白9的最重要和最丰富的翻译后修饰之一。聚糖的巨大复杂性和异质性阻碍肽&#39;MS信号10。然而，一些蛋白质组的方法已经使用这个唯一的修改，以丰富的表面蛋白，并从之前的LC-MS分析的蛋白质除去糖部分。这些方法s包括凝集素亲和捕获11和酰肼基或硼酸基化学捕获12以及亲水性色谱分离8,13。聚糖的去除转化膜蛋白常规的蛋白质，并大幅简化了MS表征。因为糖基化还发生在分泌蛋白具有高的溶解度在对比膜蛋白，许多glycoproteomic方法对可溶性蛋白进行了优化，并趋向于具有较低的糖肽的选择性和时被部署到膜蛋白8,14灵敏度。其他的方法也存在丰富，尤其细胞表面蛋白，例如那些使用超速离心15和标记策略16。表征膜蛋白我们的方法和现有的其他方法之间的详细比较了最近进行的17，结果表明，我们的方法可以执行同样出色，如果不是更好，比所有被比较的膜蛋白质组的方法，但具有更高的简易性。 为了帮助研究人员使用这种方法，我们这里详细的一般协议。这种方法综合了现有的glycoproteomics战略几个优点，特别适用于膜糖蛋白构想，但该方法同样适用于分泌蛋白。该方法的特征包括:1）膜蛋白的完全溶解，2）糖肽的糖蛋白，而不是使用固体摄像基板时，以消除潜在的空间位阻的富集，3）使用酰肼化学组成之间的共价键糖肽和捕集基板上，使得键合的糖肽可以容忍严格洗涤的高glycoselectivity，和4）的能力，以对整个捕获过程中一个管用于减少样品损失和缩短操作时间。实施这一方法来研究一个变量后，生物样品包括细胞和组织的ETY，我们观察到的高选择性（&gt; 90％），以糖蛋白8,17,18。

<table border="0" cellpadding="0" cellspacing="0" width="701">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">DTT</td>
			<td style="width:199px;">Sigma</td>
			<td style="width:119px;">646563</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">TCEP</td>
			<td style="width:199px;">Sigma</td>
			<td style="width:119px;">646547</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Iodoacetamide</td>
			<td style="width:199px;">Sigma</td>
			<td style="width:119px;">A3221</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Rapigest SF</td>
			<td style="width:199px;">Waters</td>
			<td style="width:119px;">186001860</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sodium periodate</td>
			<td style="width:199px;">Sigma</td>
			<td style="width:119px;">311448</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">PNGase F</td>
			<td style="width:199px;">New England Biolabs</td>
			<td style="width:119px;">P0704S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Affi-Gel Hz Hydrazide gel</td>
			<td style="width:199px;">Bio-Rad</td>
			<td style="width:119px;">153-6047</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Trypsin</td>
			<td style="width:199px;">Worthington Biomedical</td>
			<td style="width:119px;">LS02115</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sep-Pak C-18 cartridge</td>
			<td style="width:199px;">Waters</td>
			<td style="width:119px;">WAT054955</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Oasis MCX cartridge</td>
			<td style="width:199px;">Waters</td>
			<td style="width:119px;">186000252</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Protease inhibitor coctail</td>
			<td style="width:199px;">Sigma</td>
			<td style="width:119px;">P8340</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Urea</td>
			<td style="width:199px;">Amersco</td>
			<td style="width:119px;">568</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sodium sulphite</td>
			<td style="width:199px;">Caledon</td>
			<td style="width:119px;">8360-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Invertase</td>
			<td style="width:199px;">Sigma</td>
			<td style="width:119px;">I0408</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Alpha-1 trypsin</td>
			<td style="width:199px;">Sigma</td>
			<td style="width:119px;">F2006</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Ribonulease B</td>
			<td style="width:199px;">Sigma</td>
			<td style="width:119px;">R7884</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Avidin</td>
			<td style="width:199px;">Sigma</td>
			<td style="width:119px;">A9275</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Ovalbumin</td>
			<td style="width:199px;">Sigma</td>
			<td style="width:119px;">A5503</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Conalbumin</td>
			<td style="width:199px;">Sigma</td>
			<td style="width:119px;">C0755</td>
			<td></td>
		</tr>
	</tbody>
</table>

glycopeptide capture for cell surface proteomics

细胞表面蛋白，包括胞外基质蛋白，参与所有主要的细胞过程和功能，例如生长，分化和增殖。这些蛋白质的综合表征为生物标志物的发现，细胞类型识别和药物靶点的选择，以及帮助推动我们的细胞生物学和生理学的了解丰富的信息。表面蛋白，然而，构成，因为它们固有的低丰度，高疏水性，并且重的翻译后修饰显著分析挑战。采取上表面蛋白的糖基化常见的优点，我们在这里介绍一种高通量糖肽捕获方法，集成的现有的几种N-glycoproteomics装置的优点。我们的方法可以丰富从表面的蛋白质所产生的糖肽，并删除其聚糖，使用LC-MS浅显的蛋白质组学研究。该解决N-glycoproteome包括INFormation蛋白质的身份和数量，以及糖基化他们的网站。此方法已被应用到了一系列的研究领域，包括癌症，神经干细胞，和药物毒性。该方法的局限性在于表面的膜蛋白，这样，需要相对大量的样品进行该分析相比，研究集中于胞质蛋白的丰度低。

在实验过程中的代表性流程图总结在图1的标签，并进一步分馏步骤是可选的，细节将在近期公布18描述。另一种方法是分析未修饰的肽，其不与树脂反应。分析所述未修饰的肽的优点包括:非糖基化的肽类和蛋白质，例如在紧密连接claudins的电位标识;一个附加的优点是更准确的定量。基于这些优势，我们称之为这种方法 g lycocapture - 一个ssisted-G的叶形q uantitative <...

Watch this Scientific Journal Video about Glycopeptide Capture for Cell Surface Proteomics at JoVE.com

Glycopeptide Capture for Cell Surface Proteomics

细胞表面蛋白的生物学上重要的和广泛的糖基化。我们在这里介绍一个糖肽捕获的方法来溶解，丰富，并且这些去糖基化蛋白质浅显的LC-MS基础的蛋白质组学分析。

糖肽捕获的细胞表面蛋白组学

Cell surface proteins, including extracellular matrix proteins, participate in all major cellular processes and functions, such as growth, ...

glycopeptide-capture-for-cell-surface-proteomics

Research

JoVE Journal

Biology

11.2K 次观看.  Simon Fraser University. 细胞表面蛋白的生物学上重要的和广泛的糖基化。我们在这里介绍一个糖肽捕获的方法来溶解，丰富，并且这些去糖基化蛋白质浅显的LC-MS基础的蛋白质组学分析。 

视频: Glycopeptide Capture for Cell Surface Proteomics

Cell Capture Using a Microfluidic Device

细胞捕获使用一个微流体装置

科研

生物学

Orthogonal Protein Purification Facilitated by a Small Bispecific Affinity Tag

Due to the high costs associated with purification of recombinant proteins the protocols need to be rationalized. For high-throughput efforts there is a demand for general methods that do not require target protein specific optimization1 . To achieve this, purification tags that genetically can be fused to the gene of interest are commonly used2 . The most widely used affinity handle is the hexa-histidine tag, which is suitable for purification under both native and denaturing conditions3 . The metabolic burden for producing the tag is low, but it does not provide as high specificity as competing affinity chromatography based strategies1,2.
Here, a bispecific purification tag with two different binding sites on a 46 amino acid, small protein domain has been developed. The albumin-binding domain is derived from Streptococcal protein G and has a strong inherent affinity to human serum albumin (HSA). Eleven surface-exposed amino acids, not involved in albumin-binding4 , were genetically randomized to produce a combinatorial library. The protein library with the novel randomly arranged binding surface (Figure 1) was expressed on phage particles to facilitate selection of binders by phage display technology. Through several rounds of biopanning against a dimeric Z-domain derived from Staphylococcal protein A5, a small, bispecific molecule with affinity for both HSA and the novel target was identified6 .
The novel protein domain, referred to as ABDz1, was evaluated as a purification tag for a selection of target proteins with different molecular weight, solubility and isoelectric point. Three target proteins were expressed in Escherishia coli with the novel tag fused to their N-termini and thereafter affinity purified. Initial purification on either a column with immobilized HSA or Z-domain resulted in relatively pure products. Two-step affinity purification with the bispecific tag resulted in substantial improvement of protein purity. Chromatographic media with the Z-domain immobilized, for example MabSelect SuRe, are readily available for purification of antibodies and HSA can easily be chemically coupled to media to provide the second matrix.
This method is especially advantageous when there is a high demand on purity of the recovered target protein. The bifunctionality of the tag allows two different chromatographic steps to be used while the metabolic burden on the expression host is limited due to the small size of the tag. It provides a competitive alternative to so called combinatorial tagging where multiple tags are used in combination1,7.

A novel and highly efficient two-step affinity chromatography protocol has been developed and is described in detail. The method is based on a small purification tag with two inherent affinities and is applicable to a wide range of target proteins with different properties.

由一个小型的双特异性亲和标签的推动正交蛋白质纯化

Due to the high costs associated with purification of recombinant proteins the protocols need to be rationalized. For high-throughput efforts there is a ...

High-throughput Crystallization of Membrane Proteins Using the Lipidic Bicelle Method

Membrane proteins (MPs) play a critical role in many physiological processes such as pumping specific molecules across the otherwise impermeable membrane bilayer that surrounds all cells and organelles. Alterations in the function of MPs result in many human diseases and disorders; thus, an intricate understanding of their structures remains a critical objective for biological research. However, structure determination of MPs remains a significant challenge often stemming from their hydrophobicity. 
MPs have substantial hydrophobic regions embedded within the bilayer. Detergents are frequently used to solubilize these proteins from the bilayer generating a protein-detergent micelle that can then be manipulated in a similar manner as soluble proteins. Traditionally, crystallization trials proceed using a protein-detergent mixture, but they often resist crystallization or produce crystals of poor quality. These problems arise due to the detergent&prime;s inability to adequately mimic the bilayer resulting in poor stability and heterogeneity. In addition, the detergent shields the hydrophobic surface of the MP reducing the surface area available for crystal contacts. To circumvent these drawbacks MPs can be crystallized in lipidic media, which more closely simulates their endogenous environment, and has recently become a de novo technique for MP crystallization.
Lipidic cubic phase (LCP) is a three-dimensional lipid bilayer penetrated by an interconnected system of aqueous channels1. Although monoolein is the lipid of choice, related lipids such as monopalmitolein and monovaccenin have also been used to make LCP2. MPs are incorporated into the LCP where they diffuse in three dimensions and feed crystal nuclei. A great advantage of the LCP is that the protein remains in a more native environment, but the method has a number of technical disadvantages including high viscosity (requiring specialized apparatuses) and difficulties in crystal visualization and manipulation3,4. Because of these technical difficulties, we utilized another lipidic medium for crystallization-bicelles5,6 (Figure 1). Bicelles are lipid/amphiphile mixtures formed by blending a phosphatidylcholine lipid (DMPC) with an amphiphile (CHAPSO) or a short-chain lipid (DHPC). Within each bicelle disc, the lipid molecules generate a bilayer while the amphiphile molecules line the apolar edges providing beneficial properties of both bilayers and detergents. Importantly, below their transition temperature, protein-bicelle mixtures have a reduced viscosity and are manipulated in a similar manner as detergent-solubilized MPs, making bicelles compatible with crystallization robots. 
Bicelles have been successfully used to crystallize several membrane proteins5,7-11 (Table 1). This growing collection of proteins demonstrates the versatility of bicelles for crystallizing both alpha helical and beta sheet MPs from prokaryotic and eukaryotic sources. Because of these successes and the simplicity of high-throughput implementation, bicelles should be part of every membrane protein crystallographer&prime;s arsenal. In this video, we describe the bicelle methodology and provide a step-by-step protocol for setting up high-throughput crystallization trials of purified MPs using standard robotics.

Bicelles are lipid/amphiphile mixtures that maintain membrane proteins (MPs) within a lipid bilayer but have unique phase behavior that facilitates high-throughput screening by crystallization robots. This technique has successfully produced a number of high-resolution structures from both prokaryotic and eukaryotic sources. This video describes protocols for generating the lipidic bicelle mixture, incorporating MPs into the bicelle mixture, setting up crystallizations trials (manually as well as robotically) and harvesting crystals from the medium.

使用油脂全线Bicelle方法的膜蛋白的高通量结晶

Membrane proteins (MPs) play a critical role in many physiological processes such as pumping specific molecules across the otherwise impermeable membrane ...

Avidity-based Extracellular Interaction Screening (AVEXIS) for the Scalable Detection of Low-affinity Extracellular Receptor-Ligand Interactions

Extracellular protein:protein interactions between secreted or membrane-tethered proteins are critical for both initiating intercellular communication and ensuring cohesion within multicellular organisms. Proteins predicted to form extracellular interactions are encoded by approximately a quarter of human genes1, but despite their importance and abundance, the majority of these proteins have no documented binding partner. Primarily, this is due to their biochemical intractability: membrane-embedded proteins are difficult to solubilise in their native conformation and contain structurally-important posttranslational modifications. Also, the interaction affinities between receptor proteins are often characterised by extremely low interaction strengths (half-lives &lt; 1 second) precluding their detection with many commonly-used high throughput methods2. 
Here, we describe an assay, AVEXIS (AVidity-based EXtracellular Interaction Screen) that overcomes these technical challenges enabling the detection of very weak protein interactions (t1/2 &le; 0.1 sec) with a low false positive rate3. The assay is usually implemented in a high throughput format to enable the systematic screening of many thousands of interactions in a convenient microtitre plate format (Fig. 1). It relies on the production of soluble recombinant protein libraries that contain the ectodomain fragments of cell surface receptors or secreted proteins within which to screen for interactions; therefore, this approach is suitable for type I, type II, GPI-linked cell surface receptors and secreted proteins but not for multipass membrane proteins such as ion channels or transporters.
The recombinant protein libraries are produced using a convenient and high-level mammalian expression system4, to ensure that important posttranslational modifications such as glycosylation and disulphide bonds are added. Expressed recombinant proteins are secreted into the medium and produced in two forms: a biotinylated bait which can be captured on a streptavidin-coated solid phase suitable for screening, and a pentamerised enzyme-tagged (&beta;-lactamase) prey. The bait and prey proteins are presented to each other in a binary fashion to detect direct interactions between them, similar to a conventional ELISA (Fig. 1). The pentamerisation of the proteins in the prey is achieved through a peptide sequence from the cartilage oligomeric matrix protein (COMP) and increases the local concentration of the ectodomains thereby providing significant avidity gains to enable even very transient interactions to be detected. By normalising the activities of both the bait and prey to predetermined levels prior to screening, we have shown that interactions having monomeric half-lives of 0.1 sec can be detected with low false positive rates3.

Avidity-based Extracellular Interaction Screening AVEXIS for the Scalable Detection of Low-affinity Extracellular Receptor-Ligand Interactions

AVEXIS is a high throughput protein interaction assay developed to systematically screen for novel extracellular receptor-ligand pairs involved in cellular recognition processes. It is specifically designed to detect transient protein interactions that are difficult to identify using other high throughput approaches.

基于亲和力，外的相互作用筛选（AVEXIS）外低亲和力受体 - 配体相互作用的可扩展检测

Extracellular protein:protein interactions between secreted or membrane-tethered proteins are critical for both initiating intercellular communication and ...

Metabolic Labeling and Membrane Fractionation for Comparative Proteomic Analysis of Arabidopsis thaliana Suspension Cell Cultures

Plasma membrane microdomains are features based on the physical properties of the lipid and sterol environment and have particular roles in signaling processes. Extracting sterol-enriched membrane microdomains from plant cells for proteomic analysis is a difficult task mainly due to multiple preparation steps and sources for contaminations from other cellular compartments. The plasma membrane constitutes only about 5-20% of all the membranes in a plant cell, and therefore isolation of highly purified plasma membrane fraction is challenging. A frequently used method involves aqueous two-phase partitioning in polyethylene glycol and dextran, which yields plasma membrane vesicles with a purity of 95% 1. Sterol-rich membrane microdomains within the plasma membrane are insoluble upon treatment with cold nonionic detergents at alkaline pH. This detergent-resistant membrane fraction can be separated from the bulk plasma membrane by ultracentrifugation in a sucrose gradient 2. Subsequently, proteins can be extracted from the low density band of the sucrose gradient by methanol/chloroform precipitation. Extracted protein will then be trypsin digested, desalted and finally analyzed by LC-MS/MS. Our extraction protocol for sterol-rich microdomains is optimized for the preparation of clean detergent-resistant membrane fractions from Arabidopsis thaliana cell cultures.
We use full metabolic labeling of Arabidopsis thaliana suspension cell cultures with K15NO3 as the only nitrogen source for quantitative comparative proteomic studies following biological treatment of interest 3. By mixing equal ratios of labeled and unlabeled cell cultures for joint protein extraction the influence of preparation steps on final quantitative result is kept at a minimum. Also loss of material during extraction will affect both control and treatment samples in the same way, and therefore the ratio of light and heave peptide will remain constant. In the proposed method either labeled or unlabeled cell culture undergoes a biological treatment, while the other serves as control 4.

Metabolic Labeling and Membrane Fractionation for Comparative Proteomic Analysis of Arabidopsis thaliana Suspension Cell Cultures

Here we describe a robust method for the fractionation of plant plasma membranes into detergent resistant and detergent soluble membranes based on a mixture of unlabeled and in vivo fully 15N labeled Arabidopsis thaliana cell cultures. The procedure is applied for comparative proteomic studies to understand signaling processes.

代谢标记和膜分馏的比较蛋白质组学分析<em&gt;拟南芥</em&gt;悬浮细胞培养

Plasma membrane microdomains are features based on the physical properties of the lipid and sterol environment and have particular roles in signaling ...

Capture Compound Mass Spectrometry - A Powerful Tool to Identify Novel c-di-GMP Effector Proteins

Considerable progress has been made during the last decade towards the identification and characterization of enzymes involved in the synthesis (diguanylate cyclases) and degradation (phosphodiesterases) of the second messenger c-di-GMP. In contrast, little information is available regarding the molecular mechanisms and cellular components through which this signaling molecule regulates a diverse range of cellular processes. Most of the known effector proteins belong to the PilZ family or are degenerated diguanylate cyclases or phosphodiesterases that have given up on catalysis and have adopted effector function. Thus, to better define the cellular c-di-GMP network in a wide range of bacteria experimental methods are required to identify and validate novel effectors for which reliable in silico predictions fail.
We have recently developed a novel Capture Compound Mass Spectrometry (CCMS) based technology as a powerful tool to biochemically identify and characterize c-di-GMP binding proteins. This technique has previously been reported to be applicable to a wide range of organisms1. Here we give a detailed description of the protocol that we utilize to probe such signaling components. As an example, we use Pseudomonas aeruginosa, an opportunistic pathogen in which c-di-GMP plays a critical role in virulence and biofilm control. CCMS identified 74% (38/51) of the known or predicted components of the c-di-GMP network. This study explains the CCMS procedure in detail, and establishes it as a powerful and versatile tool to identify novel components involved in small molecule signaling.

The ubiquitous second messenger c-di-GMP controls growth and behavior of many bacteria. We have developed a novel Capture Compound Mass Spectrometry based technology to biochemically identify and characterize c-di-GMP binding proteins in virtually any bacterial species.

捕获复合质谱 - 一个强大的工具来确定新型C-二GMP效应蛋白

Considerable progress has been made during the last decade towards the identification and characterization of enzymes involved in the synthesis ...

Cell Surface Marker Mediated Purification of iPS Cell Intermediates from a Reprogrammable Mouse Model

Mature cells can be reprogrammed to a pluripotent state. These so called induced pluripotent stem (iPS) cells are able to give rise to all cell types of the body and consequently have vast potential for regenerative medicine applications. Traditionally iPS cells are generated by viral introduction of transcription factors Oct-4, Klf-4, Sox-2, and c-Myc (OKSM) into fibroblasts. However, reprogramming is an inefficient process with only 0.1-1% of cells reverting towards a pluripotent state, making it difficult to study the reprogramming mechanism. A proven methodology that has allowed the study of the reprogramming process is to separate the rare intermediates of the reaction from the refractory bulk population. In the case of mouse embryonic fibroblasts (MEFs), we and others have previously shown that reprogramming cells undergo a distinct series of changes in the expression profile of cell surface markers which can be used for the separation of these cells. During the early stages of OKSM expression successfully reprogramming cells lose fibroblast identity marker Thy-1.2 and up-regulate pluripotency associated marker Ssea-1. The final transition of a subset of Ssea-1 positive cells towards the pluripotent state is marked by the expression of Epcam during the late stages of reprogramming. Here we provide a detailed description of the methodology used to isolate reprogramming intermediates from cultures of reprogramming MEFs. In order to increase experimental reproducibility we use a reprogrammable mouse strain that has been engineered to express a transcriptional transactivator (m2rtTA) under control of the Rosa26 locus and OKSM under control of a doxycycline responsive promoter. Cells isolated from these mice are isogenic and express OKSM homogenously upon addition of doxycycline. We describe in detail the establishment of the reprogrammable mice, the derivation of MEFs, and the subsequent isolation of intermediates during reprogramming into iPS cells via fluorescent activated cells sorting (FACS).

Mouse embryonic fibroblast can be reprogrammed into induced pluripotent stem cells at low efficiency by the forced expression of transcription factors Oct-4, Sox-2, Klf-4, c-Myc. The rare intermediates of the reprogramming reaction are FACS isolated via labeling with antibodies against cell surface makers Thy-1.2, Ssea-1, and Epcam.

的iPS细胞从中间体可重编程小鼠模型的细胞表面标志物介导的净化

Mature cells can be reprogrammed to a pluripotent state. These so called induced pluripotent stem (iPS) cells are able to give rise to all cell types of ...

Non-enzymatic, Serum-free Tissue Culture of Pre-invasive Breast Lesions for Spontaneous Generation of Mammospheres

Breast ductal carcinoma in situ (DCIS), by definition, is proliferation of neoplastic epithelial cells within the confines of the breast duct, without breaching the collagenous basement membrane. While DCIS is a non-obligate precursor to invasive breast cancers, the molecular mechanisms and cell populations that permit progression to invasive cancer are not fully known. To determine if progenitor cells capable of invasion existed within the DCIS cell population, we developed a methodology for collecting and culturing sterile human breast tissue at the time of surgery, without enzymatic disruption of tissue.
Sterile breast tissue containing ductal segments is harvested from surgically excised breast tissue following routine pathological examination. Tissue containing DCIS is placed in nutrient rich, antibiotic-containing, serum free medium, and transported to the tissue culture laboratory. The breast tissue is further dissected to isolate the calcified areas. Multiple breast tissue pieces (organoids) are placed in a minimal volume of serum free medium in a flask with a removable lid and cultured in a humidified CO2 incubator. Epithelial and fibroblast cell populations emerge from the organoid after 10 - 14 days. Mammospheres spontaneously form on and around the epithelial cell monolayer. Specific cell populations can be harvested directly from the flask without disrupting neighboring cells. Our non-enzymatic tissue culture system reliably reveals cytogenetically abnormal, invasive progenitor cells from fresh human DCIS lesions.

Primary cell culture using intact tissue organoids provides a model system that mimics the multi-cellular in vivo microenvironment. We developed a serum-free primary breast epithelium tissue culture model that perpetuates mixed cell culture lineages and exhibits differentiated morphology, without enzymatic tissue disruption. Breast organoids remain viable for &#62;6 months.

非酶中，预浸润性乳腺癌病变的无血清组织培养的微球体的自然发生

Breast ductal carcinoma in situ (DCIS), by definition, is proliferation of neoplastic epithelial cells within the confines of the breast duct, without ...

Selected Reaction Monitoring Mass Spectrometry for Absolute Protein Quantification

Absolute quantification of target proteins within complex biological samples is critical to a wide range of research and clinical applications. This protocol provides step-by-step instructions for the development and application of quantitative assays using selected reaction monitoring (SRM) mass spectrometry (MS). First, likely quantotypic target peptides are identified based on numerous criteria. This includes identifying proteotypic peptides, avoiding sites of posttranslational modification, and analyzing the uniqueness of the target peptide to the target protein. Next, crude external peptide standards are synthesized and used to develop SRM assays, and the resulting assays are used to perform qualitative analyses of the biological samples. Finally, purified, quantified, heavy isotope labeled internal peptide standards are prepared and used to perform isotope dilution series SRM assays. Analysis of all of the resulting MS data is presented. This protocol was used to accurately assay the absolute abundance of proteins of the chemotaxis signaling pathway within RAW 264.7 cells (a mouse monocyte/macrophage cell line). The quantification of Gi2 (a heterotrimeric G-protein &#945;-subunit) is described in detail.

This protocol describes how to perform absolute quantification assays of target proteins within complex biological samples using selected reaction monitoring. It was used to accurately quantify proteins of the mouse macrophage chemotaxis signaling pathway. Target peptide selection, assay development, and qualitative and quantitative assays are described in detail.

选择反应监测质谱法进行绝对定量蛋白质

Absolute quantification of target proteins within complex biological samples is critical to a wide range of research and clinical applications. This ...

Enrichment of Extracellular Matrix Proteins from Tissues and Digestion into Peptides for Mass Spectrometry Analysis

The extracellular matrix (ECM) is a complex meshwork of cross-linked proteins that provides biophysical and biochemical cues that are major regulators of cell proliferation, survival, migration, etc. The ECM plays important roles in development and in diverse pathologies including cardio-vascular and musculo-skeletal diseases, fibrosis, and cancer. Thus, characterizing the composition of ECMs of normal and diseased tissues could lead to the identification of novel prognostic and diagnostic biomarkers and potential novel therapeutic targets. However, the very nature of ECM proteins (large in size, cross-linked and covalently bound, heavily glycosylated) has rendered biochemical analyses of ECMs challenging. To overcome this challenge, we developed a method to enrich ECMs from fresh or frozen tissues and tumors that takes advantage of the insolubility of ECM proteins. We describe here in detail the decellularization procedure that consists of sequential incubations in buffers of different pH and salt and detergent concentrations and that results in 1) the extraction of intracellular (cytosolic, nuclear, membrane and cytoskeletal) proteins and 2) the enrichment of ECM proteins. We then describe how to deglycosylate and digest ECM-enriched protein preparations into peptides for subsequent analysis by mass spectrometry.

This protocol describes a procedure for enriching ECM proteins from tissues or tumors and deglycosylating and digesting the ECM-enriched preparations into peptides to analyze their protein composition by mass spectrometry.

从富集组织及消化细胞外基质蛋白的成肽质谱分析

The extracellular matrix (ECM) is a complex meshwork of cross-linked proteins that provides biophysical and biochemical cues that are major regulators of ...