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Solución y conformaciones biológicamente relevantes de los retinales de ciclopropilo con bloqueo enantiomérico 11-cis
Yukari Fujimoto1, Nathan Fishkin, Gennaro Pescitelli
1Department of Chemistry, Columbia University, New York, New York 10027, USA.
Journal of the American Chemical Society
|June 20, 2002
Resumen
Los investigadores estudiaron el cromóforo 11-cis-retinilideno en la opsina bovina utilizando nuevos análogos bicíclicos de la retina. Solo el enantiómero beta-ciclopropilo (2a) se une a la opsin, revelando información sobre la unión y conformación de los cromóforos dentro del receptor.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Biología Molecular Biología Molecular
- La espectroscopia es una técnica de espectroscopia.
Sus antecedentes:
- Comprender la conformación del cromóforo 11-cis-retinilideno en la opsina bovina es crucial para la función del pigmento visual.
- Los grupos cicloprópicos quirales vinculados a los sistemas de polieno han entendido mal las contribuciones quirópticas.
Objetivo del estudio:
- Para investigar la conformación de la retina biciclo[5.1.0]octílica (retCPr) con bloqueo de 11-cis unida a la opsin.
- Para aclarar la contribución quiróptica de los anillos de ciclopropilo unidos a los sistemas de polieno.
- Para determinar la selectividad de unión de los enantiómeros de retCPr a la opsin.
Principales métodos:
- Síntesis y caracterización del enantiómero biciclo[5.1.0]octilo retinal bloqueado con 11-cis (retCPr).
- Espectroscopia de Resonancia Magnética Nuclear (RMN) para determinar la conformación del anillo.
- Métodos computacionales (optimización de la geometría, cálculos de CD) para modelar la estructura.
- Pruebas de unión a la opsina para evaluar la selectividad de los enantiómeros.
Principales resultados:
- La RMN reveló una conformación de silla giratoria para el anillo de siete miembros del retCPr.
- El análisis computacional mostró que el enantiómero 2a existe como diastereómeros con un giro positivo alrededor de C12-C13.
- Sólo el enantiómero beta-ciclopropilo (2a) se une a la opsina, no el alfa-enantiómero (2b).
- El efecto conjugativo de la fracción de ciclopropilo en el cromóforo es mínimo.
Conclusiones:
- El cromóforo se une al N-terminal de la opsina, entrando desde los lados de 4-metileno y 15-aldehído.
- La hendidura de unión de Opsin acomoda 11-cis-retinal con una ligera torsión positiva alrededor de C12-C13.
- Esta conformación explica la biostereoselectividad observada de retCPr 2a y reinterpreta los datos espectroscópicos anteriores.
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