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Las etapas entálpica y entrópica en el despliegue del péptido alfa-helical, de la espectroscopia láser T-jump/UV

Gurusamy Balakrishnan¹, Ying Hu, Gretchen M Bender

¹Department of Chemistry, Princeton University, Princeton, NJ 08544, USA.

Journal of the American Chemical Society

|October 4, 2007

Resumen

Estudiamos la dinámica de despliegue de la hélice alfa de la proteína utilizando la espectroscopia Raman de resonancia UV. Nuestros hallazgos revelan distintas fases entálpica y entrópica en la fusión de hélices, dependiendo de las condiciones de salto de temperatura.

Área de la Ciencia:

La biofísica es la biofísica.
Dinámica de las proteínas Dinámica de las proteínas
La espectroscopia es una técnica de espectroscopia.

Sus antecedentes:

Las hélices alfa son estructuras proteicas cruciales, pero sus mecanismos de despliegue dependientes de la temperatura no se comprenden completamente.
Estudios anteriores carecen de conocimientos detallados sobre la cinética de la fusión de la hélice.

Objetivo del estudio:

Para investigar la dinámica dependiente de la temperatura de la hélice alfa que se desarrolla en un péptido estabilizado.
Aplicar un nuevo sistema láser para el análisis espectroscópico con resolución temporal de los cambios conformacionales de las proteínas.

Principales métodos:

Utilizó un sistema láser Raman de estado sólido sintonizable NIR y UV profundo con una frecuencia de repetición de kHz.
Se empleó la espectroscopia Raman de resonancia UV excitada de 197 nm (UVRR) para mejorar la vibración de la amida.
Analizó espectros de UVRR dependientes de T y realizó saltos en T inducidos por láser.

Principales resultados:

UVRR y dicroísmo circular (CD) mostraron fracciones de hélice coincidentes a bajas temperaturas, divergiendo a temperaturas más altas.
Los saltos en T inducidos por láser revelaron desintegraciones de despliegue de hélice monoexponencial de ~ 120 ns, independientemente de la temperatura final.
Se identificó una pérdida rápida de helicidad (fase entálpica) seguida de una fase más lenta (fase entrópica).

Conclusiones:

UVRR es más sensible a la conformación de proteínas locales que CD.
El despliegue de la hélice implica distintas fases entálpica (disrupción del enlace H) y entrópica (reorientación de la cadena).
La dinámica observada está influenciada por las temperaturas iniciales y finales durante los saltos en T.

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