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Geometrías de coordinación variables en el sitio activo diiron (II) de la ribonucleótido reductasa R2
Walter C Voegtli1, Monika Sommerhalter, Lana Saleh
1Departments of Biochemistry, Molecular Biology, and Cell Biology and of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
Journal of the American Chemical Society
|December 18, 2003
Resumen
Los investigadores estudiaron la estructura de la proteína diferrous R2 de la ribonucleótido reductasa de Escherichia coli. Descubrieron que las estructuras de R2 empapadas de hierro difieren de las formas reducidas, ofreciendo nuevos conocimientos sobre los mecanismos de activación del oxígeno.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Biología Estructural Biología Estructural
- Enzimología Enzimología.
Sus antecedentes:
- La subunidad R2 de la ribonucleótido reductasa de Escherichia coli es crucial para la síntesis del ADN.
- Contiene un centro diirónico esencial para la generación de un radical tirosilo.
- Comprender el estado de diironio es clave para dilucidar la activación del oxígeno.
Objetivo del estudio:
- Determinar la estructura del reactivo diironio (II) de la forma R2 bajo condiciones fisiológicas.
- Investigar las diferencias estructurales entre R2 empapado en hierro y R2.2 químico/fotorreducido.
- Proporcionar datos estructurales consistentes con los hallazgos espectroscópicos para estudios de mecanismos de activación del oxígeno.
Principales métodos:
- Infusión de iones Fe (II) en cristales de proteínas apo R2 (tipo salvaje, R2-D84E, R2-D84E/W48F) a un pH neutro.
- Cristalografía de rayos X para determinar las estructuras de los diferentes estados R2 resultantes.
- Comparación de las estructuras obtenidas a pH neutro con las previamente determinadas a pH más bajo.
Principales resultados:
- Las estructuras de hierro empapado diferrous R2-wt y R2-D84E revelan distintas geometrías del sitio activo en comparación con las formas reducidas.
- Las estructuras de R2-wt y R2-D84E/W48F son similares en pH neutro y bajo, lo que indica que el pH no es el único factor de las diferencias observadas.
- Las estructuras determinadas se alinean mejor con los datos espectroscópicos de dicroísmo circular y dicroísmo circular magnético.
Conclusiones:
- La estructura del centro diiron (II) en R2 impregnado de hierro difiere significativamente de las formas reducidas reportadas anteriormente.
- Estos hallazgos desafían los modelos existentes y ofrecen nuevos puntos de partida estructurales para comprender el mecanismo de activación de la O.
- El estudio destaca la importancia de la determinación estructural bajo condiciones fisiológicamente relevantes.
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