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La glicosilasa de uracil-ADN actúa mediante la autocatálisis del sustrato
A R Dinner1, G M Blackburn, M Karplus
1Central Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QH, UK.
Nature
|October 19, 2001
Resumen
La glicosilasa de ADN Uracil (UDG) cataliza la reparación del ADN a través de un mecanismo disociativo paso a paso, no uno asociativo concertado. Los fosfatos del sustrato, no solo la enzima, reducen significativamente la energía de activación, revelando una contribución autocatalítica inesperada.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Biología Molecular Biología Molecular
- Biología Estructural Biología estructural.
Sus antecedentes:
- El uracil es una lesión común del ADN en los seres humanos, que surge de la desaminación de la citosina o de la desincorporación errónea de la deoxyuridina.
- Las glicosilasas de ADN, incluida la glicosilasa de uracilo-ADN (UDG), inician la reparación por escisión de la base al eliminar el uracilo del ADN.
- UDG es crucial para la replicación y reparación del ADN, extirpando el uracilo del ADN de una y dos hebras.
Objetivo del estudio:
- Para dilucidar el mecanismo catalítico de la glicosilasa de uracilo-ADN humano (UDG).
- Para investigar las contribuciones de la enzima y el sustrato a la catálisis.
- Para comparar el mecanismo UDG con las glicosilasas de ADN relacionadas.
Principales métodos:
- Se emplearon simulaciones híbridas de mecánica cuántica y mecánica molecular (QM/MM).
- Se analizaron la vía de reacción y los estados de transición para la catálisis de UDG.
- Se utilizaron métodos computacionales para estudiar las interacciones enzima-sustrato.
Principales resultados:
- La reacción procede a través de un mecanismo disociativo paso a paso, formando un catión de oxocarbenio y un anión uracilato intermedio.
- La energía de activación de la enzima es significativamente reducida por los fosfatos del sustrato, lo que indica un efecto "autocatalítico".
- La posición de cuatro grupos de fosfato estabiliza el estado de transición que determina la velocidad, lo que explica la actividad residual en los mutantes.
Conclusiones:
- El mecanismo catalítico de la UDG es gradualmente disociativo, al contrario de las propuestas anteriores.
- La estabilización derivada del sustrato, particularmente por fosfatos, juega un papel crítico en la catálisis de la UDG.
- Este mecanismo puede conservarse entre las glicosilasas de ADN relacionadas como TDG y SMUG1.
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