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Energéticas del acoplamiento negativo alostérico en el sensor de zinc S. aureus CzrArA
Nicholas E Grossoehme1, David P Giedroc
1Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, USA.
Journal of the American Chemical Society
|December 10, 2009
Resumen
La detección de zinc por Staphylococcus aureus CzrA exhibe una cooperatividad negativa en la unión al ADN, impulsada por cambios termodinámicos y estructurales distintos en la unión secuencial de iones Zn2+). Esta regulación tiene un impacto en la función de la proteína metalorreguladora.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Biología Molecular Biología Molecular
- Biología Estructural Biología estructural.
Sus antecedentes:
- Las proteínas reguladas alostéricamente controlan los procesos celulares a través de cambios conformacionales.
- La proteína CzrA de Staphylococcus aureus es un represor sensible al zinc que se une al ADN.
- Comprender la termodinámica de la interacción CzrA-ADN es crucial para la investigación de las proteínas metalorreguladoras.
Objetivo del estudio:
- Para investigar la termodinámica global del ion zinc (Zn(2+)) que se une al represor CzrA.
- Para dilucidar los mecanismos de la regulación alostérica negativa en la formación del complejo del operador CzrA-DNA (CzrO).
- Caracterizar las diferencias energéticas y dinámicas entre el CzrA libre y el complejo CzrA-CzrO.
Principales métodos:
- Se empleó calorimetría de titulación isotérmica (ITC) para medir la termodinámica de unión.
- Se analizaron los parámetros termodinámicos (ΔG, ΔH, ΔS, ΔCp) para la unión secuencial de Zn.
- Los cambios estructurales y dinámicos se inferían a partir de datos termodinámicos.
Principales resultados:
- Zn(2+) se une al CzrA libre en dos pasos con una cooperatividad homotrópica negativa (Δ(ΔG) = 1,8 kcal mol(-1)).
- El primer enlace Zn(2+) implica una mayor contribución entrópica y sugiere una transición estructural modesta.
- El segundo enlace Zn2+) apaga la dinámica interna, impulsando la cooperatividad.
- Zn(2+) que se une al complejo CzrA*CzrO también muestra cooperatividad negativa (Δ(ΔG) = 1,3 kcal mol(-1)) pero con diferentes energías y cambios estructurales mínimos.
- Un fuerte enlace negativo heterotrópico surge de las distintas estructuras apo-CzrA y CzrA*CzrO.
Conclusiones:
- El estudio revela la base termodinámica de la cooperatividad negativa en la unión CzrA-ADN.
- Diferentes transiciones estructurales y dinámicas en la unión de Zn(2+) regulan la función de CzrA.
- Los hallazgos proporcionan información sobre los mecanismos alostéricos de las proteínas metalorreguladoras.
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