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Ajuste espectral de pigmentos de cono ultravioleta: un mecanismo de bloqueo entre hélices

Sivakumar Sekharan¹, Victoria L Mooney, Ivan Rivalta

¹Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107 United States.

Journal of the American Chemical Society

|December 4, 2013

Resumen

Los pigmentos de cono ultravioleta (UV) exhiben un cromóforo único de base de Schiff sin protonar (USB11). Una mutación específica (F86Y) causa una coexistencia de ambas formas USB11 y protonadas de base Schiff (PSB11), estabilizadas por una cerradura entre hélices (IHL).

Área de la Ciencia:

La bioquímica es la bioquímica.
Biología Molecular Biología Molecular
Visión Visión Ciencia Ciencia.

Sus antecedentes:

Los pigmentos del cono ultravioleta (UV) son cruciales para comprender la evolución de la visión de los vertebrados.
Los pigmentos UV se diferencian de los pigmentos absorbentes visibles por su cromóforo de base Schiff no protonada (USB11), a diferencia de la base Schiff protonada (PSB11) en los pigmentos visibles.
Una mutación (F86Y) en los pigmentos UV conduce a una coexistencia de USB11 y PSB11 a pH fisiológico, un fenómeno que requiere una explicación molecular.

Objetivo del estudio:

Aclarar la base molecular para la coexistencia de las formas cromóforas USB11 y PSB11 a pH fisiológico.
Para investigar el papel del entorno USB11 en el ajuste espectral dentro de los pigmentos de cono UV.

Principales métodos:

Utilizó estudios de mutagénesis en el pigmento cónico ultravioleta (SHUV) del hámster siberiano.
Se empleó análisis espectroscópico (UV-vis).
Se realizaron cálculos teóricos utilizando el método DFT-QM/MM (SORCI+Q//B3LYP/6-31G(d): Amber96).

Principales resultados:

La mutación F86Y induce la formación del cromóforo PSB11.
Esta forma de PSB11 está estabilizada por un "bloqueo entre hélices" (IHL) que involucra redes de enlaces de hidrógeno entre las hélices transmembrana TM6, TM2 y TM3.
Los residuos específicos de aminoácidos (Y265, F86Y, G117, S118, A114, E113) y la molécula de agua w2c son parte integral de la HLI.

Conclusiones:

El mecanismo de bloqueo entre hélices (IHL) estabiliza la forma protonada de base Schiff (PSB11) en pigmentos UV mutados.
El IHL restringe el desplazamiento de la hélice transmembrana TM6, lo que afecta al ajuste espectral en los pigmentos UV.
Este estudio proporciona información molecular sobre los mecanismos de ajuste y activación espectral de los pigmentos de cono UV.

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