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Cómo la enzima de adición de CCA selecciona la adenina sobre la citosina en la posición 76 del tRNA
Baocheng Pan1, Yong Xiong, Thomas A Steitz
1Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
Science (New York, N.Y.)
|November 13, 2010
Resumen
Las enzimas de adición de CCA seleccionan la adenosina para la adición del extremo 3' del tRNA. El análisis estructural revela un mecanismo asistido por carboxilato para la incorporación de adenina, lo que explica la discriminación contra la citosina en la posición 76.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Biología Molecular Biología Molecular
- Biología Estructural Biología estructural.
Sus antecedentes:
- Las enzimas de adición de CCA (ATP ((CTP): nucleotidiltransferasas del tRNA) catalizan la adición independiente de la plantilla de CCA a los extremos 3' del tRNA.
- El mecanismo de selección de la citosina en la posición 75 se entiende, pero la selección de la adenina en la posición 76 sigue sin estar clara.
Objetivo del estudio:
- Para dilucidar el mecanismo de selección de adenina en la posición 76 durante la adición de tRNA CCA.
- Investigar la base estructural para la discriminación contra la incorporación de citidina en la posición 76.
Principales métodos:
- Cocristalografía de complejos enzimáticos de adición de CCA con imitaciones de tRNA y trifosfatos nucleósidos.
- Análisis de las interacciones enzima-sustrato en estados catalíticamente activos.
Principales resultados:
- Cinco estructuras cocristalinas revelan la incorporación de adenosina 5'-monofosfato en A76 a través de un mecanismo de iones de un metal asistido por carboxilato.
- El aspartato 110 actúa como una base general en el proceso catalítico.
- La discriminación contra CTP en la posición 76 se debe a la colocación inadecuada de fosfato α causada por la interacción de C-arginina 224, que impide el ataque nucleófilo.
Conclusiones:
- El estudio proporciona un mecanismo estructural para la selección de adenina en la posición 76 del tRNA.
- Los hallazgos aclaran cómo las enzimas que agregan CCA logran especificidad en la maduración del tRNA.
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