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Published on: December 19, 2011
El origen de la perturbación electrostática en el acetoacetato descarboxilasa
Meng-Chiao Ho1, Jean-François Ménétret, Hiro Tsuruta
1Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118-2394, USA.
Nature
|May 22, 2009
Resumen
La acetoacetato descarboxilasa (AADasa) desplaza el pKa de un residuo clave de lisina no a través de interacciones electrostáticas, sino colocándolo en un embudo hidrofóbico, revelando nuevos conocimientos sobre el mecanismo enzimático.
Área de la Ciencia:
- Enzimología Enzimología.
- Biología Estructural Biología estructural.
- La bioquímica es la bioquímica.
Sus antecedentes:
- La acetoacetato descarboxilasa (AADasa) es una enzima modelo para el estudio de los desplazamientos de pKa en los sitios activos.
- Una hipótesis de larga data sugirió que la proximidad de Lys 116 causó la perturbación pKa de Lys 115 en AADase.
- La falta previa de estructura 3D obstaculizó la verificación de esta hipótesis.
Objetivo del estudio:
- Para aclarar la base estructural para el desplazamiento pKa significativo de Lys 115 en AADase.
- Para investigar el papel de Lys 116 en el mecanismo catalítico de la AADasa.
- Para resolver la discrepancia entre la hipótesis y la evidencia experimental con respecto a la perturbación pKa de la AADasa.
Principales métodos:
- Cristalografía de rayos X de la AADasa.
- Cristalografía de rayos X del adducto de AADasa-enamina con 2,4-pentanediona.
Principales resultados:
- Se determinaron las estructuras 3D de la AADasa y su adducto de enamina.
- Contrariamente a la hipótesis, Lys 116 está orientado lejos de Lys 115.
- Lys 115 está anclado en un embudo hidrofóbico, con Lys 116 estabilizando su posición.
Conclusiones:
- El desplazamiento pKa de Lys 115 en la AADasa se debe principalmente a la desolución dentro de un embudo hidrofóbico.
- Lys 116 estabiliza a Lys 115, lo que facilita la descarboxilación a través de efectos electrostáticos y estéricos.
- La AADasa emplea un nuevo mecanismo que implica la desolución del núcleo de la proteína para la perturbación de la pKa.
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