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Catalytic Cycle of the N-Acetylglucosaminidase NagZ from Pseudomonas aeruginosa

Acebrón, Iván, Mahasenan, Kiran V., De Benedetti, Stefania, Lee, Mijoon, Artola-Recolons, Cecilia, Hesek, Dusan, Wang, Huan, Hermoso, Juan A., Mobashery, Shahriar
Journal of the American Chemical Society 2017 v.139 no.20 pp. 6795-6798
Pseudomonas aeruginosa, X-radiation, active sites, beta-lactamase, beta-lactams, catalysts, catalytic activity, gene expression, glycosidases, histidine, hydrolysis, models, molecular dynamics, mutagenesis, zinc
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.