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Cambios estructurales inducidos por la luz y el sitio de la formación de enlaces O=O en PSII capturados por XFEL

Michihiro Suga¹, Fusamichi Akita^1,2, Michihiro Sugahara³

¹Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima Naka, Okayama 700-8530, Japan.

|February 21, 2017

Resumen

Los investigadores utilizaron la cristalografía de rayos X de resolución temporal para observar los cambios estructurales en el fotosistema II (PSII) después de dos destellos de luz. Esto reveló pasos clave en la oxidación del agua, incluida la formación del enlace O = O en el complejo de evolución de oxígeno (OEC).

Área de la Ciencia:

La biofísica
Biología estructural
Investigación de la fotosíntesis

Sus antecedentes:

El fotosistema II (PSII) es un complejo proteico crucial que realiza la oxidación del agua impulsada por la luz.
El complejo de evolución de oxígeno (OEC) dentro de PSII contiene un grupo de Mn4CaO5 responsable de la división del agua.
La comprensión del mecanismo de formación de bonos O=O en PSII se ha visto limitada por la falta de datos estructurales intermedios.

Objetivo del estudio:

Elucidar el mecanismo estructural de la formación de enlaces O=O durante la oxidación del agua en el fotosistema II.
Para capturar y analizar los estados estructurales intermedios inducidos por la iluminación.
Proporcionar conocimientos a nivel atómico sobre el ciclo catalítico del complejo de oxígeno en evolución.

Principales métodos:

Cristalografía de femtosegundos en serie con resolución de tiempo utilizando un láser de electrones libres de rayos X (XFEL).
Iluminación del PSII con dos destellos de luz a temperatura ambiente.
Análisis de la diferencia isomorfa de los mapas de Fourier comparando los estados adaptados a dos destellos y a la oscuridad.

Principales resultados:

Se observaron cambios estructurales alrededor de la región Q<0xE2><0x82><0x99>/ hierro no hemo, indicando transferencia de electrones y protones.
Una molécula de agua cerca del cúmulo Mn4CaO5 desapareció, y la transferencia de protones ocurrió alrededor de la OEC.
Se identificó un nuevo átomo de oxígeno (O6) cerca del puente O5 μ4-oxo, lo que sugiere la formación del enlace O = O a una distancia de 1,5 Å.

Conclusiones:

El estudio proporciona evidencia estructural para el mecanismo de formación de enlaces O=O en el Fotosistema II.
Los hallazgos apoyan un mecanismo propuesto que implica la inserción de un nuevo átomo de oxígeno en la OEC.
La cristalografía XFEL con resolución de tiempo es una herramienta poderosa para visualizar estados transitorios en procesos biológicos.

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