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La histidina neutra y la transferencia de electrones fotoinducida en las fotoliasas de ADN
1Department of Biomolecular Mechanisms, Max-Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany. Tatjana.Domratcheva@mpimf-heidelberg.mpg.de
Journal of the American Chemical Society
|October 6, 2011
Resumen
Este estudio revela que la protonación de His365 facilita la transferencia espontánea de electrones y protones para la reparación de (6-4) fotoproducto, a diferencia del mecanismo fotoinducido para los dímeros de pirimidina de ciclobutan (CPD). Se propone un modelo de reparación unificado.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Biología Molecular Biología Molecular
- La fotoquímica es la fotoquímica.
Sus antecedentes:
- La radiación UV induce daños en el ADN, principalmente los dímeros de pirimidina de ciclobutano (CPD) y los fotoproductos de pirimidina-pirimidona (6-4).
- La CPD y la fotoliasa (6-4) son enzimas activadas por la luz que reparan estas lesiones distintas del ADN.
- Las estructuras similares de estas fotoliasas plantean preguntas sobre sus distintos mecanismos de reparación para fotoproductos químicamente diferentes.
Objetivo del estudio:
- Investigar los mecanismos moleculares subyacentes a la reparación de CPD y (6-4) fotoproducto por sus respectivas fotolasas.
- Para aclarar el papel del cofactor de dinucleótido de adenina flavinada (FADH(-)) y los residuos del sitio activo en el proceso de reparación del ADN.
- Proponer un modelo unificado para la reparación de ambos tipos de lesiones del ADN inducidas por rayos UV.
Principales métodos:
- Utilizó el enfoque computacional XMCQDPT2-CASSCF para modelar los espectros de excitación de las regiones del sitio activo.
- Analizó la estructura electrónica y los mínimos de energía de los intermediarios de reacción.
- Investigó la influencia de la protonación de la histidina en la dinámica de la transferencia de electrones y protones.
Principales resultados:
- La protonación de His365, junto con el donante de anión hidroquinona, desencadena la transferencia espontánea de electrones acoplados a protones al fotoproducto (6-4).
- El estado de energía más bajo corresponde a un biradical neutralizado, lo que indica un intermedio estable.
- El fotoproducto N3'-protonado (6-4) exhibe una alta afinidad electrónica, lo que apoya el mecanismo propuesto.
- El mecanismo de reparación de los fotoproductos (6-4) implica la transferencia neutra de His365 y el grupo hidroxilo, lo que difiere de la literatura anterior.
Conclusiones:
- La reparación de los fotoproductos (6-4) es facilitada por la transferencia espontánea de electrones acoplados a protones mediada por el neutro His365.
- La estructura electrónica del anión radical del fotoproducto (6-4) es similar a la del anión radical CPD.
- Se propone un modelo unificado que explique la reparación de ambos CPD y (6-4) fotoproducto, destacando las características mecánicas conservadas.
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