Nos gustaría agradecer a Thomas Bell, Lyn Mattathil, Mark Mannino y Neej Patel por su soporte técnico. Este trabajo fue financiado por concesión de servicio de salud pública de Estados Unidos R15DK102122 del Instituto Nacional de Diabetes y digestivo y enfermedades del riñón (NIDDK) a Jonathan Fisher. El contenido del manuscrito es responsabilidad exclusiva de los autores y no representan necesariamente la opinión oficial de la NIDDK o los institutos nacionales de salud.

Nota: Vea la figura 1 para una descripción esquemática de los pasos claves.
1. ensayo de reducción de WST-1
<ol><li>Crecer y diferenciar las células adherentes C2C12 utilizando estándar de la célula cultura procedimientos7 en una placa de 96 pozos utilizando filas A-f.<ol>
<li>Utilizar un medio de diferenciación que consta de medio modificado Eagle de Dulbecco (DMEM) suplementado con 2% de suero de caballo, 100 U/mL de penicilina y estreptomicina de 0,1 mg/mL. Incube las células a 37 ° C con 5% CO2.</li>
		<li>Al medirse la implicación de ascorbato en tPMET, suplemento de medios de diferenciación con el ácido ascórbico de 100 μm. Permitir que las células al incubar en medio de la diferenciación para ~ 24-48 h.</li>
	</ol>
</li>
	<li>Preparar soluciones WST-1 y PMS.<ol>
<li>Para hacer un stock de 10 mM de WST-1, disolver 0,033 g de WST-1 (peso fórmula (PF): 651.34 g/mol) en 5 mL de fosfato tampón salino (PBS). Almacenar a 4 ° C.</li>
		<li>Para hacer un stock de 5 mM del PMS, disolver 0,0023 g de PMS (FW: 306.34 g/mol) en 1,5 mL de desionizada H2O (diH2O). Almacenar a-20 ° C y proteger de la luz.</li>
	</ol>
</li>
	<li>Añadir 0,0108 g de glucosa, para una concentración final de 5 mM a 11,4 mL de PBS o HEPES tamponada con solución salina (HBS; sal de sodio HEPES 20 mM, 140 mM NaCl, KCl, 2, 5 mM de MgSO4, de 5 mM 1 mM CaCl2). Añadir 480 μl de 10 mM WST-1 para una concentración final de 400 μm y 48 μl de 5 mM PMS para una concentración final de 20 μm.</li>
	<li>Al medirse la implicación de ascorbato en tPMET, divida la solución en dos alícuotas de 6 mL. A una alícuota, añadir 6 μl de diH2O y a la otra alícuota agregar 6 μl de 2 kU/mL AO para una concentración final de 2 U/mL.</li>
	<li>Al medirse la implicación de superóxido en tPMET, divida la solución en dos alícuotas de 6 mL. A una alícuota, agregar 55 μl de 0,1 M KPO4 tampón y a la otra alícuota agregar 55 μl de 6.5 kU/mL de sodio a una concentración final de 60 U/mL.</li>
	<li>Lavar las células con PBS. Aspire el medio y agregar 150 μL PBS. Luego aspirar el PBS. Nota: El ensayo se realiza con las células plateadas, adjuntadas. Así, hay no hay centrifugación o el uso de la tripsina en el proceso de lavado.</li>
	<li>Añada 100 μl de solución de WST-1 (-) SOD o (-) AO a las columnas 1-6 y agregar 100 μl de solución de WST-1 (+) de sodio o (+) AO para columnas 7-12 en la placa de 96 pocillos. Utilizar filas G y H como controles de fondo (es decir, para monitorear el cambio en la absorbancia del reactivo solamente en pozos sin células).</li>
	<li>Los valores de absorbancia con el espectrofotómetro cada 10 min durante 1 h a 438 nm.</li>
	<li>Después de la lectura, los medios de comunicación de aspirar y lavar cada pozo con 150 μL de PBS. Luego aspirar el PBS.</li>
	<li>Calcular el cambio en la absorbancia de cada pocillo restando la absorbancia inicial para un pozo de la absorbencia en cualquier momento para bien. Corregir este cambio para el cambio en la absorbencia (si cualquier) observado en los pozos de fondo (es decir, pozos con solución de ensayo pero sin células).</li>
	<li>Para el análisis, normalizar los datos de absorbancia para el control de medición de 60 minutos o lavar los pocillos con PBS o HBS y luego realizar un análisis de proteína bicinchoninic ácido (BCA).</li>
	<li>Añadir albúmina de suero bovino (BSA) estándar de 2 mg/mL (rango de 0.5-2 μL para la curva estándar, dependiendo del grado de confluencia de las células) en los pocillos vacíos (filas G y H), luego añadir el reactivo BCA en todos los pocillos.</li>
	<li>Cuantificar los datos mediante nmol de WST-1 reducción por μg de proteína. Utilizar 37 mM-1 cm-1 22 como el coeficiente de extinción para WST-1 reducida en 438 nm.</li>
</ol>2. ensayo de reducción de DPIP
<ol><li>Crecer y diferenciar células adherentes C2C12 con el mismo procedimiento que el paso 1.1.</li>
	<li>Preparar solución DPIP stock 10 mM como sigue. Disolver 0,029 g de DPIP (FW: 290.08 g/mol) en 10 mL de diH2O. confirmar la concentración de DPIP midiendo absorbancia a 600 nm con un espectrofotómetro. Utilizar 1 mM-1 cm-1 23 como el coeficiente de extinción para la DPIP reducida a 600 nm. Almacenar a 4 ° C.</li>
	<li>Añadir a 11,880 mL de PBS para una concentración final de 5 mM 0,0108 g de glucosa. Añadir 120 μl de 10 mM DPIP para una concentración final de 100 μm.</li>
	<li>Al medirse la implicación de ascorbato en tPMET, divida la solución en dos alícuotas de 6 mL. A una alícuota, añadir 6 μl de diH2O y a la otra alícuota agregar 6 μl de 2 kU/mL AO para una concentración final de 2 U/mL.</li>
	<li>Al medirse la implicación de superóxido en tPMET, divida la solución en dos alícuotas de 6 mL. A una alícuota, agregar 55 μl de 0,1 M KPO4 tampón y a la otra alícuota agregar 55 μl de 6.5 kU/mL de sodio a una concentración final de 60 U/mL.</li>
	<li>Los medios de comunicación de aspirar y lavar las células en 150 μL de PBS. Aspire el PBS y añadir 100 μl de solución de DPIP (-) SOD o (-) AO a las columnas 1-6 y agregar 100 μl de solución de DPIP (+) de sodio o (+) AO para columnas 7-12 en la placa de 96 pocillos. Utilizar filas G y H será como controles de fondo (es decir, para monitorear el cambio en la absorbancia del reactivo solamente en pozos sin células).</li>
	<li>Medir la absorbancia a 600 nm utilizando espectrofotómetro cada 10 minutos para 1 h. cuantificar el cambio en absorbancia con respecto al control en el minuto 60 similar a pasos 1.9-1.13.</li>
</ol>3. determinación de si los aceptadores del electrón reducida son sustratos para AO o TEPES
<ol><li>Añadir a 5,436 mL de PBS o HBS, 240 μl de 10 mM WST-1 para una concentración final de 400 μm y 24 μl de 5 mM PMS para una concentración final de 20 μm.<ol>
<li>De DPIP, añadir 60 μL de 10 mM DPIP, para una concentración final de 100 μm, a 5,940 mL de PBS o HBS.</li>
	</ol>
</li>
	<li>Añada 100 μl de solución para cada bien en una placa de 96 pocillos de fondo plano en la ausencia de células y medir la absorbancia en un espectrofotómetro a 438 nm, para WST-1 y 600 nm, de DPIP.</li>
	<li>Añadir 1 μl de ascorbato 10 mM a la mitad de los pozos a una concentración final de 100 μM. Monitorear la absorbancia hasta que se estabilice.</li>
	<li>Estabilización, añadir 1 μl de 200 U/mL AO para una concentración final de 2 U/mL en cada pocillo o añadir 1 μl de césped de 6 kU/mL para una concentración final de 60 U/mL a cada uno bien y monitorear la absorbancia de 1 h.</li>
</ol>

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G., Babcock, G. T., Dye, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Properties+of+5-methylphenazinium+methyl+sulfate.+Reaction+of+the+oxidized+form+with+NADH+and+of+the+reduced+form+with+oxygen.">Properties of 5-methylphenazinium methyl sulfate. Reaction of the oxidized form with NADH and of the reduced form with oxygen.</a> J Biol Chem. 257 (3), 1458-1461 (1982).</li><li>Maghzal, G. J., Krause, K. H., Stocker, R., Jaquet, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+of+reactive+oxygen+species+derived+from+the+family+of+NOX+NADPH+oxidases.">Detection of reactive oxygen species derived from the family of NOX NADPH oxidases.</a> Free Radic Biol Med. 53 (10), 1903-1918 (2012).</li></ol>

Los autores no tienen nada que revelar.

Hemos presentado dos métodos para utilizar aceptadores del electrón extracelular, WST-1 y DPIP, en ensayos espectrofotométricos para controlar tPMET en miotubos C2C12. Con el crecimiento de líneas celulares en los procedimientos de cultivo estándar y un lector espectrofotómetro de placas, es posible monitorizar tPMET con estos aceptadores del electrón en un análisis simple de la microplaca. WST-1 reducción es reproducible de pozo a pozo dentro de un ensayo, pero existe variabilidad día a día. El día a día co...

La capacidad de las membranas de plasma purificadas para reducir aceptadores del electrón ha llevado a la vista que la membrana plasmática tiene una capacidad inherente de redox de1. Visto previamente en hongos, plantas y animales, tPMET es un proceso común a múltiples organismos2,3,4,5. En concreto, este proceso ha sido demostrado en Saccharomyces cerevisiae, zanahoria células, eritrocitos, linfocitos, osteosarcoma, melanoma, macrófagos, músculo esquelético y neutrófilos2,3, 4 , 5 , 6 , 7. en un proceso que transporta electrones a través de la membrana de plasma para reducir oxidantes extracelulares, tPMET participa en muchas funciones celulares incluyendo: célula crecimiento5,8, de la viabilidad de la célula9, hierro metabolismo10,11,12,13y la protección de especies de oxígeno reactivo12,14,15de señalización de la célula. Debido a la implicación de tPMET en muchas funciones celulares, un desequilibrio de tPMET ha presumido para contribuir al desarrollo de algunas condiciones de salud graves, incluyendo cáncer16,17de las enfermedades cardiovasculares, metabólicos y síndrome18.
Hay varias formas para controlar a la transferencia de electrones a través de la membrana del plasma, pero es la técnica más ampliamente utilizada evaluar la reducción de los aceptores de electrones extracelular a través de análisis colorimétricos. Aceptadores del electrón extracelular comúnmente utilizados son las sales de tetrazolio, DPIP, FeCN y ferricytochrome c19,20. La sal de tetrazolio más comúnmente utilizado es una segunda generación sal conocida como WST-119. Este compuesto es más fácil de utilizar en el análisis colorimétricos en comparación a las sales de tetrazolio de primera generación debido a dos grupos sulfonato, que aumentan su solubilidad de agua21. WST-1, junto con el intermedio electrón aceptador 1-metoxi-phenazine methosulfate (mPMS), se reduce en eventos de transferencia de electrones solo dos. Esta reducción cambia la forma oxidada de color débil de WST-1 a un precipitado más intenso, amarillo20,22. WST-1 tiene un coeficiente de extinción molar alta de 37 x 103 M-1cm-1, conduce a un análisis alta sensibilidad21,22. DPIP también es utilizado como un aceptor de electrones extracelular para controlar tPMET. Se ha demostrado que puede reducirse extracellularly DPIP por tPMET sin la ayuda de aceptadores de electrones intermedios23,24. Debido a la ausencia de aceptadores del electrón intermedio, DPIP puede directamente electrones Pick-up de la membrana del plasma, a diferencia de WST-124. Similar a la DPIP, FeCN ha visto reducirse extracelularmente a ferrocianuro, tPMET sin la ayuda de aceptadores de electrones intermedios19,24. A diferencia de WST-1 y DPIP, FeCN tiene un coeficiente de extinción molar baja conduce a un menor análisis sensibilidad9. Otro aceptor de electrones extracelular utilizados para monitorear tPMET es ferricytochrome c. Similar a WST-1, ferricytochrome c reducción aumenta con el uso del aceptador del electrón intermedio, mPMS22. A diferencia de WST-1 sin embargo, el método c ferricytochrome es menos sensible debido a una alta formación y un coeficiente de extinción molar baja22.
Aquí presentamos un método para el análisis en tiempo real de tPMET a través de análisis espectrofotométricos. El método utilizado los aceptadores del electrón extracelular WST-1 y DPIP, pues ambos tienen un coeficiente de extinción molar alta mientras que siendo menos costosa en comparación con los otros comúnmente utilizados aceptadores del electrón extracelular como c ferricytochrome. Utilizamos phenazine methosulfate (PMS) en lugar de multiprocesamiento tienen una composición química similar y PMS es mucho menos costoso. mPMS es fotoquímicamente estable que es una característica importante de un kit comercial que necesita una larga vida útil. Sin embargo, hacemos PMS fresca para cada ensayo, por lo que la estabilidad no debe ser un problema. También presentamos un método para evaluar posibles interacciones enzimáticas (ver figura 1) entre el aceptador del electrón extracelulares y enzimas que pueden ser utilizadas para caracterizar el proceso de tPMET. En concreto, las enzimas AO y el césped puede ser utilizado determinan la parte de tPMET es debido al transporte de ascorbato o liberación de superóxido extracelular, dos métodos comunes para los electrones que se transportará a través de la membrana plasmática.

<table>
	<tbody>
		<tr>
			<td>C2C12 myoblasts</td>
			<td>American Type Culture Collection&#160;</td>
			<td>CRL-1772</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s modified eagle&#39;s medium - low glucose</td>
			<td>Sigma</td>
			<td>D6046</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Plex animal serum complex</td>
			<td>Gemini Bio-Products&#160;</td>
			<td>100-602</td>
			<td></td>
		</tr>
		<tr>
			<td>penicillin-streptomycin</td>
			<td>Sigma</td>
			<td>516106</td>
			<td></td>
		</tr>
		<tr>
			<td>horse serum</td>
			<td>Gibco Technologies</td>
			<td>16050-130</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s phosphate buffered saline</td>
			<td>Sigma</td>
			<td>D8537</td>
			<td></td>
		</tr>
		<tr>
			<td>trypsin-EDTA</td>
			<td>Sigma</td>
			<td>T4049</td>
			<td></td>
		</tr>
		<tr>
			<td>15 cm culture dishes</td>
			<td>TPP</td>
			<td>93150</td>
			<td></td>
		</tr>
		<tr>
			<td>96 well culture plates</td>
			<td>TPP</td>
			<td>92096</td>
			<td></td>
		</tr>
		<tr>
			<td>2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium Sodium Salt (WST-1)</td>
			<td>Accela ChemBio&#160; Inc</td>
			<td>SY016315</td>
			<td></td>
		</tr>
		<tr>
			<td>phenazine methosulfate&#160;</td>
			<td>Sigma</td>
			<td>P9625</td>
			<td></td>
		</tr>
		<tr>
			<td>L-ascorbic acid</td>
			<td>Sigma</td>
			<td>A5960</td>
			<td></td>
		</tr>
		<tr>
			<td>ascorbate oxidase&#160;</td>
			<td>Sigma</td>
			<td>A0157</td>
			<td></td>
		</tr>
		<tr>
			<td>superoxide dismutase&#160;</td>
			<td>Sigma</td>
			<td>S5395</td>
			<td></td>
		</tr>
		<tr>
			<td>2,6-dichloroindophenol sodium salt&#160;</td>
			<td>ICN Biomedicals</td>
			<td>215011825</td>
			<td></td>
		</tr>
		<tr>
			<td>D-(+)-glucose</td>
			<td>Sigma</td>
			<td>G7528</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES sodium salt</td>
			<td>Sigma</td>
			<td>H3784</td>
			<td></td>
		</tr>
		<tr>
			<td>sodium chloride</td>
			<td>Sigma</td>
			<td>S7653</td>
			<td></td>
		</tr>
		<tr>
			<td>potassium chloride</td>
			<td>Fisher Scientific&#160;</td>
			<td>BP366</td>
			<td></td>
		</tr>
		<tr>
			<td>magnesium sulfate heptahydrate</td>
			<td>Sigma</td>
			<td>M5921</td>
			<td></td>
		</tr>
		<tr>
			<td>calcium chloride dihydrate</td>
			<td>Sigma</td>
			<td>C7902</td>
			<td></td>
		</tr>
		<tr>
			<td>potassium phosphate</td>
			<td>Fisher Scientific&#160;</td>
			<td>BP363</td>
			<td></td>
		</tr>
		<tr>
			<td>Pierce BCA Protein Assay Kit</td>
			<td>Thermo Scientific</td>
			<td>23225</td>
			<td></td>
		</tr>
		<tr>
			<td>Powerwave X-I spectrophotometer</td>
			<td>Biotek Insturments</td>
			<td>discontinued&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Spectronic Genesys 5 Spectrophotometer</td>
			<td>Thermo Scientific</td>
			<td>336001</td>
			<td></td>
		</tr>
		<tr>
			<td>PureGrade 96-well microplate, F-bottom, clear, untreated, non-sterile</td>
			<td>MidSci</td>
			<td>781602</td>
			<td></td>
		</tr>
		<tr>
			<td>Iron (II) chloride tetrahydrate</td>
			<td>Sigma</td>
			<td>220299</td>
			<td></td>
		</tr>
		<tr>
			<td>Iron (II) sulfate heptahydrate</td>
			<td>Sigma</td>
			<td>215422</td>
			<td></td>
		</tr>
		<tr>
			<td>hypoxanthine</td>
			<td>Sigma</td>
			<td>H9636</td>
			<td></td>
		</tr>
		<tr>
			<td>xanthine oxidase</td>
			<td>Sigma</td>
			<td>X4500</td>
			<td></td>
		</tr>
		<tr>
			<td>Excel</td>
			<td>Microsoft</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>R Studio</td>
			<td>Rstudio</td>
			<td></td>
			<td>https://www.rstudio.com/products/rstudio/</td>
		</tr>
		<tr>
			<td>KC4</td>
			<td>Biotek Insturments</td>
			<td>discontinued&#160;</td>
			<td></td>
		</tr>
	</tbody>
</table>

measuring trans-plasma membrane electron transport by c2c12 myotubes

Transporte de electrones de la membrana trans-plasma (tPMET) desempeña un papel en la protección de las células del estrés reductor intracelular, así como protección contra el daño por oxidantes extracelulares. Este proceso de transporte de electrones de reductores intracelulares a extracelulares oxidantes no está bien definida. Aquí presentamos ensayos espectrofotométricos por C2C12 miotubos para monitorear tPMET utilizando los aceptadores del electrón extracelular: 1 sal de tetrazolio soluble en agua (WST-1) y 2, 6-dichlorophenolindophenol (DPIP o DCIP). A través de la reducción de estos aceptadores del electrón, que son capaces de controlar este proceso en un análisis en tiempo real. Con la adición de enzimas como la ascorbato oxidasa (AO) y superóxido dismutasa (SOD) para el análisis, podemos determinar que la porción de tPMET es debido a la producción de exportación o superóxido ascorbato, respectivamente. Mientras WST-1 fue demostrada para producir resultados estables con bajo fondo, DPIP pudo ser nuevamente oxidado después de la adición de la AO y césped, que se demostró con análisis espectrofotométrico. Este método demuestra un análisis espectrofotométrico en tiempo real, multi-bien, rápido con ventajas sobre otros métodos utilizados para controlar tPMET como ferricianuro (FeCN) y reducción c ferricytochrome.

Las estadísticas se realizaron con ANOVA con medidas repetidas utilizando el software estadístico de RStudio25. Tamaños de muestra se indican en las leyendas de la figura.
Para controlar tPMET, miotubos C2C12 se utilizaron junto con aceptadores del electrón extracelular, WST-1 y DPIP. AO se utilizó para determinar que porción del WST-1 y reducción de DPIP fue debido a la emanación de ascorbato y c...

Watch this Scientific Journal Video about Measuring Trans-Plasma Membrane Electron Transport by C2C12 Myotubes at JoVE.com

Measuring Trans-Plasma Membrane Electron Transport by C2C12 Myotubes

Medición de transporte de electrones membrana Trans-Plasma por C2C12 miotubos

El objetivo de este protocolo es espectrofotometría monitor plasma trans membrana transporte de electrones utilizando aceptadores del electrón extracelular y analizar las interacciones enzimáticas que pueden ocurrir con estos aceptadores del electrón extracelular.

Trans-plasma membrane electron transport (tPMET) plays a role in protection of cells from intracellular reductive stress as well as protection from damage ...

measuring-trans-plasma-membrane-electron-transport-by-c2c12-myotubes

Research

JoVE Journal

Biochemistry

6.8K vistas.  Saint Louis University. El objetivo de este protocolo es espectrofotometría monitor plasma trans membrana transporte de electrones utilizando aceptadores del electrón extracelular y analizar las interacciones enzimáticas que pueden ocurrir con estos aceptadores del electrón extracelular.

Video: Measuring Trans-Plasma Membrane Electron Transport by C2C12 Myotubes

Method to Visualize and Analyze Membrane Interacting Proteins by Transmission Electron Microscopy

Monotopic proteins exert their function when attached to a membrane surface, and such interactions depend on the specific lipid composition and on the availability of enough area to perform the function. Nanodiscs are used to provide a membrane surface of controlled size and lipid content. In the absence of bound extrinsic proteins, sodium phosphotungstate-stained nanodiscs appear as stacks of coins when viewed from the side by transmission electron microscopy (TEM). This protocol is therefore designed to intentionally promote stacking; consequently, the prevention of stacking can be interpreted as the binding of the membrane-binding protein to the nanodisc. In a further step, the TEM images of the protein-nanodisc complexes can be processed with standard single-particle methods to yield low-resolution structures as a basis for higher resolution cryoEM work. Furthermore, the nanodiscs provide samples suitable for either TEM or non-denaturing gel electrophoresis. To illustrate the method, Ca2+-induced binding of 5-lipoxygenase on nanodiscs is presented.

Many proteins perform their function when attached to membrane surfaces. The binding of extrinsic proteins on nanodisc membranes can be indirectly imaged by transmission electron microscopy. We show that the characteristic stacking (rouleau) of nanodiscs induced by the negative stain sodium phosphotungstate is prevented by the binding of extrinsic protein.

Método para visualizar y analizar de membrana Interactuando Proteínas por Microscopía Electrónica de Transmisión

Monotopic proteins exert their function when attached to a membrane surface, and such interactions depend on the specific lipid composition and on the ...

Investigación

Bioquímica

Measuring Protein Binding to F-actin by Co-sedimentation

Filamentous actin (F-actin) organization within cells is regulated by a large number of actin-binding proteins that control actin nucleation, growth, cross-linking and/or disassembly. This protocol describes a technique &#8211; the actin co-sedimentation, or pelleting, assay &#8211; to determine whether a protein or protein domain binds F-actin and to measure the affinity of the interaction (i.e., the dissociation equilibrium constant). In this technique, a protein of interest is first incubated with F-actin in solution. Then, differential centrifugation is used to sediment the actin filaments, and the pelleted material is analyzed by SDS-PAGE. If the protein of interest binds F-actin, it will co-sediment with the actin filaments. The products of the binding reaction (i.e., F-actin and the protein of interest) can be quantified to determine the affinity of the interaction. The actin pelleting assay is a straightforward technique for determining if a protein of interest binds F-actin and for assessing how changes to that protein, such as ligand binding, affect its interaction with F-actin.

This protocol describes a method to test the ability of a protein to co-sediment with filamentous actin (F-actin) and, if binding is observed, to measure the affinity of the interaction.

Medición de la unión de proteínas a actina F por co-sedimentación

Filamentous actin (F-actin) organization within cells is regulated by a large number of actin-binding proteins that control actin nucleation, growth, ...

Analyzing Supercomplexes of the Mitochondrial Electron Transport Chain with Native Electrophoresis, In-gel Assays, and Electroelution

The mitochondrial electron transport chain (ETC) transduces the energy derived from the breakdown of various fuels into the bioenergetic currency of the cell, ATP. The ETC is composed of 5 massive protein complexes, which also assemble into supercomplexes called respirasomes (C-I, C-III, and C-IV) and synthasomes (C-V) that increase the efficiency of electron transport and ATP production. Various methods have been used for over 50 years to measure ETC function, but these protocols do not provide information on the assembly of individual complexes and supercomplexes. This protocol describes the technique of native gel polyacrylamide gel electrophoresis (PAGE), a method that was modified more than 20 years ago to study ETC complex structure. Native electrophoresis permits the separation of ETC complexes into their active forms, and these complexes can then be studied using immunoblotting, in-gel assays (IGA), and purification by electroelution. By combining the results of native gel PAGE with those of other mitochondrial assays, it is possible to obtain a completer picture of ETC activity, its dynamic assembly and disassembly, and how this regulates mitochondrial structure and function. This work will also discuss limitations of these techniques. In summary, the technique of native PAGE, followed by immunoblotting, IGA, and electroelution, presented below, is a powerful way to investigate the functionality and composition of mitochondrial ETC supercomplexes.

This protocol describes the separation of functional mitochondrial electron transport chain complexes (Cx) I-V and supercomplexes thereof using native electrophoresis to reveal information about their assembly and structure. The native gel can be subjected to immunoblotting, in-gel assays, and purification by electroelution to further characterize individual complexes.

Análisis de supercomplexes de la cadena de transporte de electrones mitocondriales con electroforesis nativa, ensayos en gel y electroelución

The mitochondrial electron transport chain (ETC) transduces the energy derived from the breakdown of various fuels into the bioenergetic currency of the ...

Semi-automated Biopanning of Bacterial Display Libraries for Peptide Affinity Reagent Discovery and Analysis of Resulting Isolates

Biopanning bacterial display libraries is a proven technique for peptide affinity reagent discovery for recognition of both biotic and abiotic targets. Peptide affinity reagents can be used for similar applications to antibodies, including sensing and therapeutics, but are more robust and able to perform in more extreme environments. Specific enrichment of peptide capture agents to a protein target of interest is enhanced using semi-automated sorting methods which improve binding and wash steps and therefore decrease the occurrence of false positive binders. A semi-automated sorting method is described herein for use with a commercial automated magnetic-activated cell sorting device with an unconstrained bacterial display sorting library expressing random 15-mer peptides. With slight modifications, these methods are extendable to other automated devices, other sorting libraries, and other organisms. A primary goal of this work is to provide a comprehensive methodology and expound the thought process applied in analyzing and minimizing the resulting pool of candidates. These techniques include analysis of on-cell binding using fluorescence-activated cell sorting (FACS), to assess affinity and specificity during sorting and in comparing individual candidates, and the analysis of peptide sequences to identify trends and consensus sequences for understanding and potentially improving the affinity to and specificity for the target of interest.

Biopanning bacterial display libraries is a proven technique for discovery of peptide affinity reagents, a robust alternative to antibodies. The semi-automated sorting method herein has streamlined biopanning to decrease the occurrence of false positives. Here we illustrate the thought process and techniques applied in evaluating candidates and minimizing downstream analysis.

Biopanning semi-automatizado de bibliotecas de exhibición bacteriana péptido afinidad reactivo descubrimiento y análisis de los aislamientos que

Biopanning bacterial display libraries is a proven technique for peptide affinity reagent discovery for recognition of both biotic and abiotic targets. ...

Electrochemical Detection of Deuterium Kinetic Isotope Effect on Extracellular Electron Transport in Shewanella oneidensis MR-1

Direct electrochemical detection of c-type cytochrome complexes embedded in the bacterial outer membrane (outer membrane c-type cytochrome complexes; OM c-Cyts) has recently emerged as a novel whole-cell analytical method to characterize the bacterial electron transport from the respiratory chain to the cell exterior, referred to as the extracellular electron transport (EET). While the pathway and kinetics of the electron flow during the EET reaction have been investigated, a whole-cell electrochemical method to examine the impact of cation transport associated with EET has not yet been established. In the present study, an example of a biochemical technique to examine the deuterium kinetic isotope effect (KIE) on EET through OM c-Cyts using a model microbe, Shewanella oneidensis MR-1, is described. The KIE on the EET process can be obtained if the EET through OM c-Cyts acts as the rate-limiting step in the microbial current production. To that end, before the addition of D2O, the supernatant solution was replaced with fresh media containing a sufficient amount of the electron donor to support the rate of upstream metabolic reactions, and to remove the planktonic cells from a uniform monolayer biofilm on the working electrode. Alternative methods to confirm the rate-limiting step in microbial current production as EET through OM c-Cyts are also described. Our technique of a whole-cell electrochemical assay for investigating proton transport kinetics can be applied to other electroactive microbial strains.

Electrochemical Detection of Deuterium Kinetic Isotope Effect on Extracellular Electron Transport in Shewanella oneidensis MR-1

Here we present a protocol of whole-cell electrochemical experiments to study the contribution of proton transport to the rate of extracellular electron transport via the outer-membrane cytochromes complex in Shewanella oneidensis MR-1.

Electroquímico detección de deuterio cinético isótopo efecto en extracelular transporte de electrones en la Shewanella oneidensis MR-1

Direct electrochemical detection of c-type cytochrome complexes embedded in the bacterial outer membrane (outer membrane c-type cytochrome complexes; OM ...

Analysis of &#946;-Amyloid-induced Abnormalities on Fibrin Clot Structure by Spectroscopy and Scanning Electron Microscopy

This article presents methods for generating in vitro fibrin clots and analyzing the effect of beta-amyloid (A&#946;) protein on clot formation and structure by spectrometry and scanning electron microscopy (SEM). A&#946;, which forms neurotoxic amyloid aggregates in Alzheimer&#39;s disease (AD), has been shown to interact with fibrinogen. This A&#946;-fibrinogen interaction makes the fibrin clot structurally abnormal and resistant to fibrinolysis. A&#946;-induced abnormalities in fibrin clotting may also contribute to cerebrovascular aspects of the AD pathology such as microinfarcts, inflammation, as well as, cerebral amyloid angiopathy (CAA). Given the potentially critical role of neurovascular deficits in AD pathology, developing compounds which can inhibit or lessen the A&#946;-fibrinogen interaction has promising therapeutic value. In vitro methods by which fibrin clot formation can be easily and systematically assessed are potentially useful tools for developing therapeutic compounds. Presented here is an optimized protocol for in vitro generation of the fibrin clot, as well as analysis of the effect of A&#946; and A&#946;-fibrinogen interaction inhibitors. The clot turbidity assay is rapid, highly reproducible and can be used to test multiple conditions simultaneously, allowing for the screening of large numbers of A&#946;-fibrinogen inhibitors. Hit compounds from this screening can be further evaluated for their ability to ameliorate A&#946;-induced structural abnormalities of the fibrin clot architecture using SEM. The effectiveness of these optimized protocols is demonstrated here using TDI-2760, a recently identified A&#946;-fibrinogen interaction inhibitor.

Presented here are two methods that can be used individually or in combination to analyze the effect of beta-amyloid on fibrin clot structure. Included is a protocol for creating an in vitro fibrin clot, followed by clot turbidity and scanning electron microscopy methods.

Análisis de anomalías inducida por β-amiloide en la estructura del coágulo de fibrina por espectroscopía y microscopía electrónica de barrido

This article presents methods for generating in vitro fibrin clots and analyzing the effect of beta-amyloid (A&#946;) protein on clot formation and ...

A Fluorescence Fluctuation Spectroscopy Assay of Protein-Protein Interactions at Cell-Cell Contacts

A variety of biological processes involves cell-cell interactions, typically mediated by proteins that interact at the interface between neighboring cells. Of interest, only few assays are capable of specifically probing such interactions directly in living cells. Here, we present an assay to measure the binding of proteins expressed at the surfaces of neighboring cells, at cell-cell contacts. This assay consists of two steps: mixing of cells expressing the proteins of interest fused to different fluorescent proteins, followed by fluorescence fluctuation spectroscopy measurements at cell-cell contacts using a confocal laser scanning microscope. We demonstrate the feasibility of this assay in a biologically relevant context by measuring the interactions of the amyloid precursor-like protein 1 (APLP1) across cell-cell junctions. We provide detailed protocols on the data acquisition using fluorescence-based techniques (scanning fluorescence cross-correlation spectroscopy, cross-correlation number and brightness analysis) and the required instrument calibrations. Further, we discuss critical steps in the data analysis and how to identify and correct external, spurious signal variations, such as those due to photobleaching or cell movement.
In general, the presented assay is applicable to any homo- or heterotypic protein-protein interaction at cell-cell contacts, between cells of the same or different types and can be implemented on a commercial confocal laser scanning microscope. An important requirement is the stability of the system, which needs to be sufficient to probe diffusive dynamics of the proteins of interest over several minutes.

This protocol describes a fluorescence fluctuation spectroscopy-based approach to investigate interactions among proteins mediating cell-cell interactions, i.e. proteins localized in cell junctions, directly in living cells. We provide detailed guidelines on instrument calibration, data acquisition and analysis, including corrections to possible artefact sources.

Un análisis de espectroscopia de fluorescencia fluctuación de interacciones de proteínas en los contactos célula-célula

A variety of biological processes involves cell-cell interactions, typically mediated by proteins that interact at the interface between neighboring ...

Analysis of Protein Folding, Transport, and Degradation in Living Cells by Radioactive Pulse Chase

Radioactive pulse-chase labeling is a powerful tool for studying the conformational maturation, the transport to their functional cellular location, and the degradation of target proteins in live cells. By using short (pulse) radiolabeling times (&lt;30 min) and tightly controlled chase times, it is possible to label only a small fraction of the total protein pool and follow its folding. When combined with nonreducing/reducing SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoprecipitation with (conformation-specific) antibodies, folding processes can be examined in great detail. This system has been used to analyze the folding of proteins with a huge variation in properties such as soluble proteins, single and multi-pass transmembrane proteins, heavily N- and O-glycosylated proteins, and proteins with and without extensive disulfide bonding. Pulse-chase methods are the basis of kinetic studies into a range of additional features, including co- and posttranslational modifications, oligomerization, and polymerization, essentially allowing the analysis of a protein from birth to death. Pulse-chase studies on protein folding are complementary with other biochemical and biophysical methods for studying proteins in vitro by providing increased temporal resolution and physiological information. The methods as described within this paper are adapted easily to study the folding of almost any protein that can be expressed in mammalian or insect-cell systems.

Here we describe a protocol for a general pulse-chase method that allows the kinetic analysis of folding, transport, and degradation of proteins to be followed in live cells.

Análisis del plegamiento de la proteína, el transporte y degradación en las células vivas por pulso radiactivo Chase

Radioactive pulse-chase labeling is a powerful tool for studying the conformational maturation, the transport to their functional cellular location, and ...

Interactions with and Membrane Permeabilization of Brain Mitochondria by Amyloid Fibrils

A growing body of evidence indicates that membrane permeabilization, including internal membranes such as mitochondria, is a common feature and primary mechanism of amyloid aggregate-induced toxicity in neurodegenerative diseases. However, most reports describing the mechanisms of membrane disruption are based on phospholipid model systems, and studies directly targeting events occurring at the level of biological membranes are rare. Described here is a model for studying the mechanisms of amyloid toxicity at the membrane level. For mitochondrial isolation, density gradient medium is used to obtain preparations with minimal myelin contamination. After mitochondrial membrane integrity confirmation, the interaction of amyloid fibrils arising from &#945;-synuclein, bovine insulin, and hen egg white lysozyme (HEWL) with rat brain mitochondria, as an in vitro biological model, is investigated. The results demonstrate that treatment of brain mitochondria with fibrillar assemblies can cause different degrees of membrane permeabilization and ROS content enhancement. This indicates structure-dependent interactions between amyloid fibrils and mitochondrial membrane. It is suggested that biophysical properties of amyloid fibrils and their specific binding to mitochondrial membranes may provide explanations for some of these observations.

Provided here is a protocol for investigating the interactions between native form, prefibrillar, and mature amyloid fibrils of different peptides and proteins with mitochondria isolated from different tissues and various areas of the brain.

Interacciones con y la permeabilización de membrana de las mitocondrias cerebrales por Amiloide Fibrils

A growing body of evidence indicates that membrane permeabilization, including internal membranes such as mitochondria, is a common feature and primary ...

Characterization of Membrane Transporters by Heterologous Expression in E. coli and Production of Membrane Vesicles

Several methods have been developed to functionally characterize novel membrane transporters. Polyamines are ubiquitous in all organisms, but polyamine exchangers in plants have not been identified. Here, we outline a method to characterize polyamine antiporters using membrane vesicles generated from the lysis of Escherichia coli cells heterologously expressing a plant antiporter. First, we heterologously expressed AtBAT1 in an E. coli strain deficient in polyamine and arginine exchange transporters. Vesicles were produced using a French press, purified by ultracentrifugation and utilized in a membrane filtration assay of labeled substrates to demonstrate the substrate specificity of the transporter. These assays demonstrated that AtBAT1 is a proton-mediated transporter of arginine, &#947;-aminobutyric acid (GABA), putrescine and spermidine. The mutant strain that was developed for the assay of AtBAT1 may be useful for the functional analysis of other families of plant and animal polyamine exchangers. We also hypothesize that this approach can be used to characterize many other types of antiporters, as long as these proteins can be expressed in the bacterial cell membrane. E. coli is a good system for the characterization of novel transporters, since there are multiple methods that can be employed to mutagenize native transporters.

Characterization of Membrane Transporters by Heterologous Expression in E. coli and Production of Membrane Vesicles

We describe a method for the characterization of proton-driven membrane transporters in membrane vesicle preparations produced by heterologous expression in E. coli and lysis of cells using a French press.

Caracterización de transportadores de membranas por expresión heteróloga en E. coli y producción de vesículas de membrana

Several methods have been developed to functionally characterize novel membrane transporters. Polyamines are ubiquitous in all organisms, but polyamine ...