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Especificidad del sustrato enzimático conferida por distintas vías de conformación

Florencia Rago1, Daniel Saltzberg2, Karen N Allen1,3

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Journal of the American Chemical Society
|October 7, 2015
PubMed
Resumen
Este resumen es generado por máquina.

Los cambios conformacionales de la enzima dictan la especificidad del sustrato. La aldolasa utiliza diferentes conformaciones para distinguir entre el 1-fosfato de fructosa y el 1,6-bisfosfato de fructosa, vinculando los cambios conformacionales a la catálisis.

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Área de la Ciencia:

  • La bioquímica
  • Cinética de las enzimas
  • Dinámica conformacional de las proteínas

Sus antecedentes:

  • La catálisis enzimática se basa en el reconocimiento del sustrato, pero la evidencia directa que vincula los cambios conformacionales de la enzima con la selectividad del sustrato es limitada.
  • La aldolasa, una enzima glicolítica clave, debe diferenciar entre el 1-fosfato de fructosa y el 1,6-bisfosfato de fructosa, lo que la convierte en un modelo ideal para estudiar la discriminación de sustratos.
  • Se sabe que los residuos específicos de las isoenzimas (ISR) distantes del sitio activo, particularmente en las hélices alfa superficiales y la región carboxilo-terminal (CTR), median las distinciones cinéticas.

Objetivo del estudio:

  • Investigar la hipótesis de que los cambios conformacionales de las enzimas subyacen a la selectividad del sustrato en la aldoasa.
  • Explorar el papel de regiones específicas, incluidas las hélices alfa superficiales y el CTR, en la mediación de estos cambios conformacionales.
  • Establecer un vínculo entre la dinámica conformacional observada y el proceso catalítico.

Principales métodos:

  • Creación de variantes de cisteína de superficie única de aldolasa para el etiquetado específico del sitio.
  • Etiquetado de variantes con fluoroforos sensibles al medio ambiente.
  • Seguimiento de los cambios conformacionales mediante espectrofotometría de emisión de fluorescencia y espectrofotometría de fluorescencia de flujo detenido.

Principales resultados:

  • Los espectros de fluorescencia de las variantes de aldoasa etiquetadas difieren en la presencia de cantidades saturantes de fructosa 1-fosfato frente a fructosa 1,6-bisfosfato, lo que indica conformaciones distintas.
  • Los cambios dependientes de la concentración del sustrato en los espectros de fluorescencia confirmaron los eventos de unión.
  • Las mediciones de fluorescencia de flujo detenido revelaron que la tasa de cambios conformacionales ocurrió en la misma escala de tiempo que la catálisis.

Conclusiones:

  • La aldolasa presenta cambios de conformación específicos del sustrato.
  • Estas dinámicas conformacionales están vinculadas al ciclo catalítico de la enzima y al reconocimiento del sustrato.
  • Los cambios conformacionales representan un posible mecanismo común para la especificidad del sustrato en enzimas con múltiples sustratos.