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Clorinación críptica por una enzima de hierro no hemo durante la biosíntesis del aminoácido ciclopropilo

Frédéric H Vaillancourt¹, Ellen Yeh, David A Vosburg

¹Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.

|August 27, 2005

Resumen

Los investigadores descubrieron nuevas enzimas, CmaB y CmaC, que biológicamente halogenan y ciclizan compuestos. Este hallazgo revela un nuevo mecanismo para la formación de anillos de ciclopropilo en la biosíntesis de productos naturales.

Área de la Ciencia:

La bioquímica es la bioquímica.
Enzimología Enzimología.
Biosíntesis de Productos Naturales Biosíntesis de Productos Naturales

Sus antecedentes:

Más de 4.000 productos naturales incorporan halógenos (cloro, bromo, yodo) durante la biosíntesis.
La halogenación tiene un impacto significativo en la bioactividad de estos productos naturales.
Las enzimas que catalizan la halogenación de grupos alifáticos no activados no fueron caracterizadas.

Objetivo del estudio:

Caracterizar nuevas enzimas involucradas en la biosíntesis del ácido coronámico (CMA).
Para dilucidar el mecanismo de formación de anillos de ciclopropano en la síntesis de CMA.
Identificar la primera enzima halogenasa conocida que actúa sobre grupos alifáticos no activados.

Principales métodos:

Investigó la actividad de cinco proteínas (CmaA, CmaB, CmaC, CmaD, CmaE) de las jeringas de Pseudomonas.
Utilizó ensayos bioquímicos para determinar las funciones enzimáticas en la construcción de CMA.
Caracterizó CmaB como una enzima Fe2+ no hemo, dependiente del alfa-cetoglutarato y CmaC como una enzima formadora de ciclopropano.

Principales resultados:

Identificó a CmaB como la primera enzima de su clase en exhibir actividad halogenasa, específicamente clorando l-alo-isoleucina en la posición gamma.
Se demostró que CmaC cataliza la formación del anillo ciclopropilo a partir del intermediario gamma-clorado.
Se estableció que CmaB y CmaC trabajan secuencialmente: gamma-halogenación seguida por la eliminación intramolecular de gamma.

Conclusiones:

La acción combinada de CmaB y CmaC representa una nueva estrategia biológica para la formación de anillos de ciclopropano a través de la halogenación y la eliminación.
Este estudio caracteriza enzimas previamente desconocidas y amplía la comprensión de la diversidad y función de la halogenasa.
Los hallazgos proporcionan información sobre la biosíntesis de fitotoxinas como la coronatina.

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