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Conocimientos estructurales sobre las diferencias en la activación de la proteína G por la familia A y la familia B

Daniel Hilger¹, Kaavya Krishna Kumar¹, Hongli Hu^1,2

¹Department of Molecular and Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive, Stanford, CA 94305, USA.

Science (New York, N.Y.)

|August 1, 2020

Resumen

Los receptores acoplados a proteínas de la familia B (GPCR), al igual que el receptor de glucagón, activan la señalización más lentamente que los receptores de la familia A debido a una ruptura estructural única en TM6. Esto afecta la regulación del metabolismo de los carbohidratos.

Área de la Ciencia:

La bioquímica
Biología estructural
Farmacología

Sus antecedentes:

Los receptores acoplados a proteínas de la familia B (GPCR) son reguladores cruciales del metabolismo de los carbohidratos.
Las características estructurales distintas, incluida una interrupción del segmento transmembrana 6 (TM6) de la hélice α, diferencian a la familia B de los GPCR de la familia A.
Comprender estas diferencias estructurales es clave para dilucidar los mecanismos de activación de los receptores.

Objetivo del estudio:

Comparar la estructura y la función del receptor de glucagón de la familia B (GCGR) con el receptor adrenérgico β2 de la familia A (β2AR).
Investigar las consecuencias funcionales de la alteración estructural del TM6 en los GPCR de la familia B.
Elucidar los mecanismos moleculares subyacentes a las tasas de activación diferencial de la proteína G.

Principales métodos:

Microscopía criolectrónica (crio-EM) para determinar la estructura del complejo proteico GCGR-Gs con una resolución de 3,1 angstroms.
Ensayos bioquímicos que miden la rotación de trifosfato de guanosina (GTP), la liberación de difosfato de guanosina (GDP), la unión a la GTP y la disociación de las proteínas G.
Espectroscopia de fluorescencia y doble resonancia de electrones (DEER) para sondear los cambios conformacionales.

Principales resultados:

La estructura cryo-EM reveló una ruptura distinta en la hélice TM6 del complejo GCGR-Gs, consistente con los GPCR de la familia B.
GCGR exhibió tasas significativamente más lentas de activación de la proteína G, incluida la rotación de GTP, la liberación de GDP y la disociación de la proteína G, en comparación con β2AR.
La unión del agonista por sí sola fue insuficiente para inducir un movimiento hacia afuera detectable en el extremo citoplasmático de TM6 en GCGR, a diferencia de β2AR.

Conclusiones:

La ruptura estructural en TM6 de las GPCR de la familia B, ejemplificada por GCGR, contribuye a una cinética de activación de la proteína G más lenta.
Este mecanismo de activación más lento puede representar un paradigma de señalización distinto para los GPCR de la familia B en la regulación de procesos fisiológicos como el metabolismo de los carbohidratos.
Las investigaciones adicionales sobre estas diferencias pueden servir de base para el desarrollo de terapias dirigidas a los trastornos metabólicos.

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