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La actividad hidratasa de la descarboxilasa de semialdehído de malonato: implicaciones mecánicas y evolutivas
Gerrit J Poelarends1, Hector Serrano, William H Johnson
1Division of Medicinal Chemistry, College of Pharmacy, and Department of Chemistry and Biochemistry, Institute for Cellular and Molecular Biology, The University of Texas, Austin, Texas 78712, USA.
Journal of the American Chemical Society
|December 2, 2004
Resumen
La descarboxilasa de semialdehído de malonato (MSAD) exhibe una nueva actividad de hidratasa, convirtiendo un sustrato específico en acetopyruvato. Esta función promiscuo, junto con su papel en la descarboxilasa, sugiere una evolución divergente dentro de la superfamilia de la tautomerasa.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Enzimología Enzimología.
- Ciencia de las proteínas Ciencia de las proteínas.
Sus antecedentes:
- La descarboxilasa de semialdehído de malonato (MSAD) pertenece a la superfamilia de las tautomerasas, que se caracteriza por un pliegue beta-alfa-beta y una prolina catalítica N-terminal.
- Las enzimas de la superfamilia de la tautomerasa comparten homología estructural y un mecanismo catalítico conservado que involucra a la prolina.
Objetivo del estudio:
- Para investigar las actividades enzimáticas de la descarboxilasa de semialdehído de malonato (MSAD).
- Aclarar el mecanismo catalítico y los orígenes evolutivos de la MSAD dentro de la superfamilia de la tautomerasa.
Principales métodos:
- Los ensayos de cinética enzimática determinan los valores de kcat/Km para la actividad de la hidratasa.
- La titulación de RMN 15N para determinar el pKa del residuo catalítico de prolina (Pro-1).
Principales resultados:
- MSAD muestra una actividad promiscua de hidratasa, convirtiendo el 2-oxo-3-pentynoate en acetopyruvate con una kcat/Km de 6.0 x 10^2 M^-1 s^-1.1.
- Pro-1 y Arg-75 son esenciales tanto para la actividad de la descarboxilasa como para la hidratasa.
- El pKa de Pro-1 se determinó como ~9.2, lo que sugiere un papel en la polarización del sustrato a través de enlaces de hidrógeno o interacciones electrostáticas.
- La actividad compartida de la hidratasa y el Pro-1 pKa con la deshalogenasa del ácido trans-3-cloroacrílico (CaaD) sugieren una evolución divergente.
Conclusiones:
- MSAD posee actividades tanto de descarboxilasa como de hidratasa promiscuas, mediadas por Pro-1 y Arg-75.
- El mecanismo catalítico probablemente implica que Pro-1 polarice el sustrato carbonilo oxígeno.
- MSAD y CaaD probablemente evolucionaron de un antepasado común, conservando las capacidades catalíticas ancestrales para la adición de conjugado de agua.
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