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Implicaciones de la ciclización de pirano y la conformación de pterina en las formas oxidadas del cofactor de

Douglas R Gisewhite¹, Jing Yang², Benjamin R Williams¹

¹Department of Chemistry , Bryn Mawr College , Bryn Mawr , Pennsylvania 19010 , United States.

Journal of the American Chemical Society

|September 12, 2018

Resumen

El cierre del anillo de pirano en los ligandos de molibdopterina (MPT) acopla electrónicamente los centros de molibdeno, modulando la actividad enzimática. Este mecanismo de conmutación molecular ajusta las propiedades redox en las enzimas de piranopterina molibdeno.

Área de la Ciencia:

Química bioorgánica
Mecanismos de las enzimas
Química organometálica

Sus antecedentes:

Las enzimas mononucleares de molibdeno y tungsteno utilizan el ligando de la molibdopterina (MPT).
El MPT contiene un quelato de ditioleno unido a un grupo de piranopterina.
Se hipotetiza que la ciclización / escisión de pirano MPT regula la reactividad del centro del metal.

Objetivo del estudio:

Investigar cómo la ciclización de pirano de MPT modula la comunicación electrónica entre las fracciones de metioleno y pterina.
Determinar cómo la ciclización de pirano altera el entorno electrónico del sitio catalítico de molibdeno.
Diseñar modelos de moléculas pequeñas del cofactor Mo-MPT para su estudio detallado.

Principales métodos:

Voltametría cíclica
Espectroscopia vibratoria (FT-IR y Raman)
Espectroscopia de absorción electrónica
Espectroscopia de absorción de rayos X

Principales resultados:

El cierre del anillo de pirano provoca cambios distintos en la frecuencia de estiramiento de MoO y el potencial de reducción de MoV/IV.
Un ligando de dihidropiranopterina está acoplado electrónicamente al grupo de Mo-dietileno a través de una conformación coplanar.
Una fuerte transición de transferencia de carga de ditionoleno → pterina es una firma espectroscópica para el sistema acoplado.
La ausencia del puente pirano conduce a la rotación de la pterina, desacoplando el sistema.

Conclusiones:

La ciclización de pirano acopla electrónicamente las unidades de pterina y diitioleno en modelos Mo-MPT.
Este acoplamiento permite que la pterina con déficit de electrones module el entorno de molibdeno.
La ciclización / escisión de pirano MPT actúa como un interruptor molecular, regulando las propiedades redox en las enzimas de piranopterina molibdeno.

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