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Evaluación de la contribución catalítica de una base general posicionada en la isomerasa cetosteroide
Vandana Lamba1, Filip Yabukarski1, Margaux Pinney1
1Department of Biochemistry, ‡Department of Chemistry, #Department of Chemical Engineering, §Stanford ChEM-H, Stanford University , Stanford, California 94305, United States.
Journal of the American Chemical Society
|July 14, 2016
Resumen
Investigando la catálisis enzimática, este estudio cuantifica la contribución de una base general en la isomerasa cetosteroide (KSI). Utilizando rescate exógeno y variadas bases de carboxilato, revela funciones catalíticas significativas, lo que sugiere mecanismos adicionales más allá del posicionamiento.
Área de la Ciencia:
- La bioquímica
- Cinética de las enzimas
- Ingeniería de proteínas
Sus antecedentes:
- Las reacciones de transferencia de protones son cruciales en los sitios activos de la enzima, empleando ácidos y bases generales.
- Identificar y cuantificar la contribución catalítica de estos residuos es un reto.
- Las mediciones efectivas de la molaridad utilizando agentes exógenos pueden estimar las funciones catalíticas, pero son propensas a sesgos estéricos y de unión.
Objetivo del estudio:
- Investigar la contribución catalítica de una base general en la isomerasa cetosteroide (KSI) utilizando el rescate exógeno.
- Evaluar y minimizar los efectos estéricos y de posicionamiento en las mediciones efectivas de la molaridad.
- Determinar el papel catalítico de la base general en el *Comamonas testosteroni* KSI (tKSI) y el *Pseudomonas putida* KSI (pKSI).
Principales métodos:
- Mutagénesis sistemática de KSI, incluida la base general y los residuos cercanos.
- Experimentos de rescate exógenos utilizando una serie de bases carboxiladas de diferentes tamaños pero con pKa similar.
- Cristalografía de rayos X de un mutante tKSI y análisis del ciclo de doble mutante.
Principales resultados:
- Se obtuvieron molaridades efectivas de consenso de aproximadamente 5 × 10^4 M para tKSI y 10^3 M para pKSI.
- El análisis estructural no mostró reordenamientos significativos en el mutante de base general.
- Los ciclos de doble mutación no indicaron efectos mutacionales de largo alcance, validando el enfoque experimental.
Conclusiones:
- Las altas molaridades efectivas sugieren fuertemente una contribución catalizadora sustancial de la base general en KSI.
- Si bien es probable que el posicionamiento juegue un papel, la magnitud del efecto implica que están involucrados mecanismos catalíticos adicionales.
- Es necesaria una amplia variación en los agentes exógenos para evaluar con precisión las contribuciones catalíticas de las enzimas.
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