Artículo del mes
mayo 2017

Catalytic Cycle of the N-Acetylglucosaminidase NagZ from Pseudomonas aeruginosa

Referencia artículo:
JACS; 2017 May 8; 139(20):6795-6798.
Desvelado el mecanismo catalítico de NagZ, una enzima clave en la resistencia a antibióticos de Pseudomonas aeruginosa NagZ de Pseudomonas aeruginosa cataliza el primer paso del reciclaje de los muropéptidos (fragmentos naturales de la pared bacteriana) en el citoplasma y regula la expresión de la -lactamasa, la enzima clave en la resistencia a antibióticos -lactámicos. Los aspectos estructurales y funcionales de la catálisis de NagZ se investigaron mediante un total de siete estructuras cristalinas, dinámica molecular y por mutagénesis dirigida. Las estructuras muestran cambios estructurales profundos requeridos para la activación y descubren al Zn como un regulador de su actividad. El trabajo proporciona una imagen de todos los pasos del ciclo catalítico de NagZ en este importante patógeno humano.
Resumen
The N-acetylglucosaminidase NagZ of Pseudomonas aeruginosa catalyzes the first cytoplasmic step in recycling of muropeptides, cell-wall-derived natural products. This reaction regulates gene expression for the β-lactam resistance enzyme, β-lactamase. The enzyme catalyzes hydrolysis of N-acetyl-β-d-glucosamine-(1→4)-1,6-anhydro-N-acetyl-β-d-muramyl-peptide (1) to N-acetyl-β-d-glucosamine (2) and 1,6-anhydro-N-acetyl-β-d-muramyl-peptide (3). The structural and functional aspects of catalysis by NagZ were investigated by a total of seven X-ray structures, three computational models based on the X-ray structures, molecular-dynamics simulations and mutagenesis. The structural insights came from the unbound state and complexes of NagZ with the substrate, products and a mimetic of the transient oxocarbenium species, which were prepared by synthesis. The mechanism involves a histidine as acid/base catalyst, which is unique for glycosidases. The turnover process utilizes covalent modification of D244, requiring two transition-state species and is regulated by coordination with a zinc ion. The analysis provides a seamless continuum for the catalytic cycle, incorporating large motions by four loops that surround the active site.
Sobre el grupo investigador