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Bases estructurales del sustrato/producto antipuerto Na(+) independiente y cooperativo en CaiT
Sabrina Schulze1, Stefan Köster, Ulrike Geldmacher
1Department of Structural Biology, Max Planck Institute of Biophysics, Max-von-Laue Strasse 3, 60438 Frankfurt am Main, Germany.
Nature
|September 11, 2010
Resumen
Los investigadores determinaron las estructuras del antiportador de carnitina / butirobetaína CaiT independiente del sodio, revelando un nuevo mecanismo para el transporte de soluto a través de membranas sin depender de los iones de sodio.
Área de la Ciencia:
- Biología estructural Biología estructural.
- El transporte por membrana es el transporte por membrana.
- La bioquímica es la bioquímica.
Sus antecedentes:
- El transporte de la membrana biológica es crucial para la vida, a menudo mediado por transportadores secundarios.
- Los transportadores de betaína/carnitina/colina (BCCT) son típicamente dependientes del sodio (Na+) o de los protones (H+).
- La naturaleza sodio-independiente de CaiT presenta un caso único dentro de la familia BCCT.
Objetivo del estudio:
- Para aclarar la base estructural de la función de antiportador de carnitina / butirobetaína (CaiT) independiente del sodio.
- Comprender el mecanismo de transporte de soluto en ausencia de dependencia de Na+ o H+.
- Para caracterizar los estados funcionales y la unión al sustrato de CaiT.
Principales métodos:
- Se utilizó la cristalografía de rayos X para determinar las estructuras de CaiT de Proteus mirabilis (PmCaiT) y Escherichia coli (EcCaiT).
- Se realizó la reconstitución de CaiT en proteoliposomas para estudios funcionales.
- Se realizaron ensayos vinculantes y análisis de la cooperatividad del sustrato.
Principales resultados:
- Las estructuras de PmCaiT (2.3-A) y EcCaiT (3.5-A) revelaron una conformación orientada hacia adentro.
- Un átomo de azufre de metionina, no un ion Na+, coordina el sustrato en el sitio de transporte de CaiT.
- EcCaiT mostró dos moléculas de butirobetaína unidas, una en el sitio de transporte y otra en un bolsillo extracelular, lo que indica una unión cooperativa.
Conclusiones:
- CaiT utiliza un nuevo mecanismo de transporte independiente del sodio que involucra la coordinación de la metionina.
- Las estructuras CaiT proporcionan una imagen completa del mecanismo de acceso alternativo.
- La unión cooperativa del sustrato, con el sitio extracelular actuando como un sitio regulador, mejora la eficiencia del transporte.
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