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Las estructuras de C3b en complejo con los factores B y D dan una idea de la formación de la convertasa del

Federico Forneris¹, Daniel Ricklin, Jin Wu

¹Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Department of Chemistry, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, Netherlands.

Science (New York, N.Y.)

|January 6, 2011

Resumen

La cascada del complemento amplifica las respuestas inmunes mediante la escisión de C3b y el factor B. Las ideas estructurales revelan cómo el factor D se une y activa este complejo, apuntando a la amplificación del complemento a las células etiquetadas con C3b.

Área de la Ciencia:

La bioquímica es la bioquímica.
Inmunología Inmunología.
Biología Estructural Biología estructural.

Sus antecedentes:

La cascada del complemento es crucial para la inmunidad innata, mediando la inflamación y el aclaramiento celular.
La amplificación del complemento se basa en el complejo C3bB, escindido por el factor D para formar convertasas activas.
Comprender este paso central es clave para controlar las respuestas inmunes.

Objetivo del estudio:

Para aclarar la base estructural del complemento pro-convertasa C3bB y su complejo con el factor D.
Para revelar el mecanismo de la escisión mediada por el factor D y la activación del complejo C3bB.
Para entender cómo la amplificación del complemento se restringe a las superficies objetivo.

Principales métodos:

Se utilizó la cristalografía de rayos X para determinar las estructuras de C3bB y su complejo con el factor D.
Se obtuvieron datos estructurales de alta resolución (4 Å y 3.5 Å).
El análisis estructural se centró en las interacciones proteína-proteína y los cambios conformacionales.

Principales resultados:

La estructura cristalina de la pro-convertasa C3bB fue determinada a una resolución de 4 Å.
La estructura del complejo C3bB-factor D se resolvió a una resolución de 3,5 Å.
La unión del factor B a C3b induce una conformación abierta y activable de C3bB, facilitando la unión y activación del factor D.

Conclusiones:

El factor D se une a un sitio alostérico en la conformación abierta del factor B, distinto del centro catalítico.
Los cambios conformacionales inducidos por el sustrato desplazan el bucle inhibidor del factor D, lo que lleva a su activación.
Este mecanismo inducido por el sustrato, dependiente del cofactor, asegura que la amplificación del complemento esté específicamente dirigida a las células opsonizadas por C3b.

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