Diese Forschung wurde von der Startfonds der Simon-Fraser-Universität unterstützt.

Ein. Ernte-Membranen <ol><li> Hinzufügen hypotonischen Puffer (10 mM Tris-HCl, 10 mM KCl, 1,5 mM MgCl 2, pH 8,0) mit Proteaseinhibitorcocktail auf einen Zellpellet (~ 10 8 Zellen) und Inkubation für 15-30 min auf Eis. Lyse der Zellen, indem die Probe durch Spritzennadeln (5-10 Durchläufe) oder Homogenisieren der Probe von einem Dounce Homogenisator (15-30 Schläge). Verwenden Sie eine Zählkammer und Trypanblaufärbung um die Effizienz der Lyse zu überprüfen. </li><li> Erhalten Sie die mikrosomale Fraktion durch eine differenzielle Zentrifugation des Lysats bei 3.000 gx 15 min und dann bei 100.000 gx 2 Stunden. Die erste Zentrifugation erhält man ein Pellet, das die Kernfraktion und die anschließende Zentrifugation des Überstandes erzeugt ein zweites Pellet, welches die Mikrosomenfraktion, die die Plasmamembran als auch membrangebundene Organellen 8 enthält. Die endgültige Überstand ist die cytosolische Fraktion. Bewahren Sie die mikrosomalen Fraktionen in -80 ° C-Gefrierschrank für weitere analysist wie nachstehend angegeben. </li></ol> 2. Auflösen, denaturieren und Digest Membranproteine <ol><li> Löse den mikrosomalen Fraktion im Denaturierungspuffer (40 mM Tris, 10 mM EDTA, 10 mM TCEP, 0,5% Rapigest, pH 8) und dann inkubieren der Lösung auf 100 ° C für 10 min. </li><li> Kühlen der erhitzten Lösung auf Raumtemperatur abgekühlt, ultrahochreinen Harnstoffpulver in der Lösung auf 8 M Endkonzentration und Inkubation der Probe bei 37 ° C für 30 min. </li><li> Hinzufügen Iodacetamid Stammlösung zu der Probe auf 15 mM Endkonzentration, und Inkubieren der Lösung in der Dunkelheit für 30 min bei Raumtemperatur, um die freien Thiole in der Probe zu alkylieren. Hinzufügen DTT-Stammlösung zu der Probe auf 10 mM Endkonzentration der Lösung und Inkubation für weitere 10 min bei Raumtemperatur, um das überschüssige Iodacetamid stillen. </li><li> Verdünnt die erhaltene Lösung 10-fach mit 40 mM Tris-Puffer bei pH 8, und anschließend Trypsin hinzufügen, um die Probe bei einer 1:20-Verhältnis von trypsin zum Gesamtprotein. Aufrechterhaltung der Aufschlussreaktion in einem 37 ° C Ofen über Nacht, um sicherzustellen, wird die Reaktion beendet. </li><li> Beenden Sie die Verdauung durch Ansäuern der Probenlösung mit HCl, ein Zustand, bricht auch das Reinigungsmittel, dh Rapigest pH 1. Verschlechtern die Rapigest bei 37 ° C für 1 h, und entfernen Sie die entstandene Niederschlag durch Zentrifugieren. </li><li> Reinigen Sie den Überstand, die Probe-Peptide enthält, die von einem C-18-Festphasenextraktion (SPE) Patrone und trocknen Sie die erhaltene Probe durch Speedvac. </li><li> Durchführen einer SDS-PAGE-Analyse von Proben vor und nach der Trypsin-Verdau, um die Effizienz der Verdauung zu bestätigen. </li></ol> 3. Glycopeptid-Capture- <ol><li> Man löst die gereinigten Peptide im Kopplungspuffer (100 mM Natriumacetat, pH 5,5). Hinzufügen Natriumperiodat in die Peptidlösung in einer Endkonzentration von 10 mM für 30 min im Dunkeln bei Raumtemperatur. Dadurch werden die cis-Diol-Gruppen in den Glycanen zu Aldehyden oxidieren, Welche die Glykane zu koppeln Harzes durch Hydrazid Chemie ermöglichen. Quenche die übermäßige Periodat durch Natriumsulfit bei einer Endkonzentration von 20 mM und pH 5 für 10 min bei Raumtemperatur. </li><li> Einführung Hydrazid-derivatisierten Harzes in die Peptidlösung in einem Verhältnis von 1:4 (Harz-Lösung) zu koppeln Glycopeptide zu dem Harz. Inkubieren der Reaktion bei 37 ° C für 1-2 Tage mit End-zu-End-Rotation für eine vollständige Kopplung. </li><li> Entfernen der nicht gebundenen Peptide durch Waschen des Harzes zweimal mit 1 ml von jeder der folgenden: DI-Wasser, 1,5 M NaCl, Methanol und 80% Acetonitril. Schließlich 3x Waschen des Harzes mit 1 ml 100 mM NH 4 HCO 3 bei pH 8, um den Puffer des Systems austauschen zu 100 mM NH 4 HCO 3. <ol><li> Sammle den Überstand und die Waschschritte für die Analyse von ungebundenen Peptiden (optional). </li></ol></li><li> Lösen der N-Glycopeptide vom Harz durch PNGase F in einer Inkubation über Nacht bei 37 ° C mitN-Ende-zu-Ende-Rotation. Sammeln Sie die freigesetzten Peptide durch Zentrifugation und einer 80% Acetonitril waschen. Trocknen Sie die erhaltene Lösung in der Speedvac für LC-MS-Analyse. </li></ol> 4. Weitere Fraktionierung (Optional) Zur weiteren Vereinfachung Probenkomplexität, Fraktionierung der N-Glycopeptiden. Beispielsweise abgeblasen, und der getrockneten Peptide in 10 mM Ammoniak-Formiat, 20% Acetonitril pH 3 und mit starken Kationenaustauscher (SCX) gereinigt, um die Peptide zu fraktionieren. Trocknen des erhaltenen Elutionsmittel und dann analysiert die erhaltenen Peptidfraktionen durch Umkehrphasen-LC-MS 8,17,18. 5. Reinigung der frei N-Glycopeptide (Optional) Wenn Bedenken erheben für die mögliche Kontamination der Peptide, wieder aufzulösen die getrockneten Peptide in 0,1% Ameisensäure und verwenden Sie einen MCX SPE-Säule, um die Peptide weiter zu reinigen, bevor Umkehrphasen-LC-MS-Analyse. <strong&gt; Hinweis: Datenbanksuchparameter. Bei der selektiven Spaltung von N-Glycopeptide aus dem Harz, wandelt die PNGase F-N-Glycan verknüpft Asparagin zu einer Asparaginsäure. Daher besteht ein 0,9840 Da Massenverschiebung der befreiten N-Glycopeptide. Diese Peptide genau zu identifizieren, muss diese Änderung der Suchparameter mit gemeinsamen Abänderungen wie der Carbamidomethylierung des Cystein und Oxidation der Methionin zugesetzt werden.

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Die Autoren erklären, dass sie keine finanziellen Interessen konkurrieren.

Hier stellen wir ein Glycopeptid-Capture-Strategie zur Profilierung Zelloberflächenproteine. Das Verfahren kann angewendet werden, um sekretierte Proteine, wie sie in Blut, wie auch in anderen Körperflüssigkeiten oder Zellkulturmedien zu studieren. Der Erfolg des Verfahrens beruht auf der vollständigen Verdau von Proben; Daher ist ein SDS-PAGE-Charakterisierung der Effizienz der Verdauung notwendig, insbesondere für die erste Zeitanalyse einer Probe. Eine vollständige Verdauung kann ei...

Zelloberflächen-Proteine ​​interagieren mit der extrazellulären Umgebung und leiten Signale von der Außenseite zur Innenseite der Zelle. Somit sind diese Proteine, einschließlich extrazellulären Matrixproteinen, spielen wichtige Rollen in allen Aspekten der Zellbiologie und der Physiologie von Proliferation, Wachstum, Migration, Differenzierung Alterung und so weiter. Oberflächenproteine ​​funktionieren durch die Interaktion mit anderen Zellen, Proteinen und kleinen Molekülen 03.01. Molekulare Charakterisierung von Zelloberflächenproteinen ist von großem Interesse, nicht nur für Biologen, sondern auch für die pharmazeutische Industrie, da mehr als 60% der Medikamente, Zelloberflächenproteine ​​4 ausgerichtet. Tandem-Massenspektrometrie (MS), mit seiner überlegenen Sensitivität, Genauigkeit und Durchsatz für die Identifizierung von Proteinen und Peptiden, wurde ein leistungsfähiges Werkzeug für die globale proteomische Studien 5,6. Doch stellen Oberflächenproteine ​​erhebliche Herausforderungen zu MS-basierte Proteomik, wiedie meisten Oberflächenproteine ​​gibt es in geringen Mengen und mit schweren Veränderungen. Die Membran-überspannenden Regionen der Oberflächenproteine ​​machen sie hydrophob ist; Dies ist insbesondere der Fall bei Multitransmembranproteine. Es ist daher schwierig, Membranproteine ​​in wässrigen Lösungen ohne Zuhilfenahme eines Detergens zu lösen; Jedoch ist die Verwendung von Waschmitteln in der Regel unterdrückt die Leistung der HPLC und MS 1,7,8 Proteinidentifikation. Daher Membranproteine ​​wurden schlecht in direkten LC-MS basierte Proteomik gekennzeichnet. Die Glykosylierung ist eine der wichtigsten und reichlich post-translationale Modifikationen, die sich in Zelloberflächenproteine ​​9. Die enorme Komplexität und Heterogenität der Glykane behindern Peptide &#39;MS-Signal 10. Dennoch haben mehrere proteomische Methoden dieses einzigartige Modifikation verwendet werden, um Oberflächenproteine ​​zu bereichern und die Zuckerreste von Proteinen vor der LC-MS-Analyse zu entfernen. Diese Methodes sind Lektin-basierte Affinitätseinfang 11 und Hydrazid-basierten oder Borsäure Chemie Capture 12 sowie hydrophile Trennungen 8,13. Die Entfernung der Glykane verwandelt Membranproteine, regelmäßige Proteine ​​und vereinfacht die MS Charakterisierung drastisch. Da Glykosylierung in sezernierte Proteine, die eine hohe Löslichkeit im Gegensatz zu Membranproteine ​​erfolgt auch, viele glycoproteomische Methoden für lösliche Proteine ​​optimiert und tendenziell niedrigere Glycopeptid Selektivität und Empfindlichkeit, wenn sie eingesetzt werden, um Proteine ​​8,14 Membran haben. Andere Verfahren bestehen auch zu bereichern, insbesondere Zelloberflächenproteine, wie z. B. jene, die Ultrazentrifugation 15 und Markierungsstrategien 16. Ein detaillierter Vergleich zwischen unserem Verfahren und anderen bestehenden Methoden zur Charakterisierung von Membranproteinen durchgeführt wurde kürzlich 17, und die Ergebnisse zeigten, daß unser Verfahren ebenso gut ausführen kann, wenn nichtbesser, als alle gegen Membran Proteomics Methoden, aber mit höheren Einfachheit. Um Forscher mit dieser Methode, die wir hier ausführlich ein allgemeines Protokoll. Diese Methode integriert mehrere Vorteile der bestehenden Glycoproteomikstrategie Strategien und ist speziell für Membran-Glykoproteine ​​entwickelt, doch die Methode funktioniert genauso gut für sekretierte Proteine. Die Merkmale dieses Verfahrens sind: 1) eine vollständige Solubilisierung von Membranproteinen, 2) eine Anreicherung von Glycopeptiden anstelle von Glykoproteinen, die potentielle sterische Behinderung zu vermeiden, wenn unter Verwendung eines festen Erfassungs Substrat, 3) die Verwendung von Hydrazid-Chemie, um kovalente Bindungen zwischen Form Glycopeptide und die Erfassung Substrat, so dass das gebundene Glycopeptide können stringente Waschungen für Hoch glycoselectivity tolerieren, und 4) die Fähigkeit, die gesamte Aufnahmevorgang in einem Rohr zur Probenverlust reduziert und verkürzt die Dauer Verfahren durchzuführen. Nach Durchführung dieses Verfahrens, um das Studium eine variableety von biologischen Proben, einschließlich Zellen und Geweben beobachteten wir eine hohe Selektivität (&gt; 90%) an Glycoproteine ​​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

Zelloberflächenproteine, einschließlich extrazellulären Matrixproteinen, sich an allen wichtigen zellulären Prozessen und Funktionen, wie Wachstum, Differenzierung und Proliferation. Eine umfassende Charakterisierung dieser Proteine ​​bietet reichhaltige Informationen zur Entdeckung von Biomarkern, Zelltyp-Identifikation und Drogenzielauswahl, als auch helfen, unser Verständnis der Zellbiologie und Physiologie voraus. Oberflächenproteine ​​stellen jedoch erhebliche analytische Herausforderungen, die aufgrund ihrer inhärent niedrigen Fluss, hohe Hydrophobie und schwere post-translationale Modifikationen. Unter Ausnutzung der vorherrschenden Glykosylierung auf Oberflächenproteine, führen wir hier ein Hochdurchsatz-Glycopeptid-Capture-Ansatz, der die Vorteile von mehreren vorhandenen N-Glycoproteomikstrategie Mittel integriert. Unsere Methode kann die Glykopeptide von Oberflächenproteinen abgeleitet bereichern und entfernen ihre Glykane für einfache Proteomik mittels LC-MS. Die beschlossene N-glycoproteome umfasst die informationen von Protein Identität und Quantität sowie ihre Websites der Glykosylierung. Dieses Verfahren hat zu einer Reihe von Studien in Bereichen wie Krebs, Stammzellen und Arzneimitteltoxizität angewendet. Die Beschränkung des Verfahrens liegt in der geringen Häufigkeit von Oberflächenmembranproteinen, so dass eine relativ große Menge von Proben für die Analyse erforderlich im Vergleich zu Studien am cytosolischen Proteine ​​zentriert.

Ein repräsentatives Flussdiagramm des experimentellen Verfahrens ist in Fig. 1 zusammengefaßt. Die Etikettierung und weitere Fraktionierung Schritte sind optional und Details sind in einer Veröffentlichung 18 beschrieben. Eine weitere Möglichkeit ist die unveränderten Peptide, die nicht mit dem Harz reagieren zu analysieren. Die Vorteile des Analysierens der unmodifizierten Peptide umfassen die Identifizierung von potentiellen nicht-glykosylierte Peptide und Proteine, wie Claudinen in ti...

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

Glycopeptide Capture for Cell Surface Proteomics

Zelloberflächen-Proteine ​​sind biologisch wichtige und weithin glykosyliert. Wir stellen hier eine Glykopeptid-Capture-Ansatz für einfache LC-MS basierte Proteomanalysen löslich zu machen, zu bereichern, und deglycosylieren diese Proteine.

Glycopeptid-Capture für Zelloberflächen Proteomics

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 Aufrufe.  Simon Fraser University.  Zelloberflächen-Proteine ​​sind biologisch wichtige und weithin glykosyliert. Wir stellen hier eine Glykopeptid-Capture-Ansatz für einfache LC-MS basierte Proteomanalysen löslich zu machen, zu bereichern, und deglycosylieren diese Proteine. 

Serie: Glycopeptide Capture for Cell Surface Proteomics

Cell Capture Using a Microfluidic Device

Zell-Capture mit einer mikrofluidischen Vorrichtung

Forschung

Biologie

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.

Orthogonal Protein Purification von einer kleinen Bispezifische Affinity Tag Facilitated

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.

High-Throughput-Kristallisation von Membranproteinen mit dem Lipidische Bicellen Methode

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.

Avidität-basierte extrazelluläre Wechselwirkung Screening (AVEXIS) für die Erkennung von Scalable Low-Affinität extrazellulären Rezeptor-Ligand-Wechselwirkungen

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.

Metabolische Markierung und Membran Fraktionierung für Vergleichende Proteomanalyse von<em&gt; Arabidopsis thaliana</em&gt; Fahrwerk Zellkulturen

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.

Capture Compound Mass Spectrometry - Ein leistungsfähiges Tool zum Identifizieren Novel c-di-GMP Effektorproteinen

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.

Zelloberflächenmarker vermittelte Reinigung von iPS-Zellen aus einer Zwischen Reprogrammierbare Maus-Modell

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.

Nicht-enzymatische, Serumfreie Zellkultur von Pre-invasive Brustläsionen für Spontane Erzeugung Mammospheres

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.

Selected Reaction Monitoring-Massenspektrometrie für Absolute Proteinquantifizierung

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.

Anreicherung von extrazellulären Matrixproteinen aus Gewebe und Verdauung in Peptide für Massenspektrometrie-Analyse

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