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Una guanina del sitio activo participa en la catálisis de la ribozima glmS en su estado protonado

Júlia Viladoms¹, Lincoln G Scott, Martha J Fedor

¹Department of Chemical Physiology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, United States.

Journal of the American Chemical Society

|September 23, 2011

Resumen

Este estudio investigó el papel catalítico de la guanina 33 (G33) en la glmS ribozima. Los resultados indican que el G33 actúa como un estabilizador del estado de transición, no como un catalizador de base general, en la escisión del ARN.

Área de la Ciencia:

La bioquímica es la bioquímica.
Biología Molecular Biología Molecular
La catálisis del ARN por ARN.

Sus antecedentes:

Las guaninas del sitio activo en las ribozimas se proponen como catalizadores de base generales.
El papel específico de G33 en la ribozima glmS de Bacillus anthracis sigue sin estar claro.

Objetivo del estudio:

Para investigar el mecanismo catalítico de G33 en el glmS ribozima.
Para determinar si G33 funciona como un catalizador de base general o juega otro papel en la escisión del ARN.

Principales métodos:

Ensayos cinéticos que miden la dependencia del pH de la escisión para los ribozimas glmS de tipo silvestre y mutantes.
Mediciones de pK basadas en la fluorescencia utilizando 8-azaguanosina en la posición 33.

Principales resultados:

Los valores aparentes de pK (a) de los ensayos cinéticos no apoyan a G33 como un catalizador de base general.
Las discrepancias en los valores de pK (a) sugieren que la desprotonación de G33 no es el paso dependiente del pH.
G33(N1) probablemente estabiliza el estado de transición a través de enlaces de hidrógeno en su forma neutra, protonada.

Conclusiones:

G33 en la ribozima glmS no funciona como un catalizador de base general.
G33 probablemente estabiliza el estado de transición catalítica a través de enlaces de hidrógeno.
Se propone un modelo catalítico alternativo para el G33.

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