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El desajuste hidrofóbico lípido-rodopsina altera el contenido helicoidal de la rodopsina
Olivier Soubias1, Shui-Lin Niu, Drake C Mitchell
1Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland 20892, USA.
Journal of the American Chemical Society
|August 21, 2008
Resumen
La estructura de la proteína de la rodopsina se adapta al grosor de la membrana lipídica, no al revés. Esta adaptabilidad de la proteína influye en su función y estabilidad dentro de la membrana celular.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Biología Estructural Biología estructural.
- Biofísica de las membranas Biofísica de las membranas.
Sus antecedentes:
- La activación de la rodopsina a la metarhodopsina II es sensible al grosor de la bicapa lipídica.
- La teoría del emparejamiento hidrofóbico sugiere que las bicapas lipídicas se ajustan elásticamente a las hélices transmembrana de proteínas.
- Existe incertidumbre sobre si las bicapas se adaptan a las proteínas o si las proteínas se adaptan a las bicapas.
Objetivo del estudio:
- Para investigar si el grosor de la bicapa se ajusta a la longitud de la proteína o si la rodopsina altera su conformación para adaptarse a la bicapa.
- Explorar la relación entre el grosor hidrofóbico de la membrana y la estructura y función de la rodopsina.
Principales métodos:
- Rodopsina bovina reconstituida y purificada en fosfatidilcolinas de diferentes longitudes de cadena de hidrocarburos (14-20 carbonos).
- espesor medido de la doble capa utilizando (2) H NMR.
- Contenido helicoidal de proteínas cuantificado a través del dicroísmo circular de la radiación sincrotrón y el dicroísmo circular convencional.
- Se han estudiado la rodopsina adaptada a la oscuridad, los fotointermedios (metarhodopsina I/II/III) y la opsin.
Principales resultados:
- El grosor de Bilayer mostró cambios mínimos tras la incorporación de rodopsina y la fotoactivación.
- El contenido helicoidal de la rodopsina aumentó con el aumento del grosor hidrofóbico de la membrana.
- El contenido helicoidal se mantuvo sin cambios tras la fotoactivación.
- El aumento de la helicidad se correlacionó con mayores proporciones de metarhodopsina II / metarhodopsina I, una formación más rápida de metarhodopsina II, una mayor fluorescencia de triptófano y temperaturas de desnaturalización más altas.
Conclusiones:
- La rodopsina exhibe una adaptabilidad significativa a las propiedades hidrofóbicas de su entorno lipídico.
- La proteína, más que la bicapa, parece ajustar su conformación en respuesta al grosor de la membrana.
- Esta adaptabilidad conformacional influye en los estados funcionales y la estabilidad de la rodopsina.
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