5KSC: E166A/R274N/R276N Toho-1 Beta-lactamase aztreonam acyl-enzyme intermediate

The monobactam antibiotic aztreonam is used to treat cystic fibrosis patients with chronic pulmonary infections colonized by Pseudomonas aeruginosa strains expressing CTX-M extended-spectrum beta-lactamases. The protonation states of active-site residues that are responsible for hydrolysis have been determined previously for the apo form of a CTX-M beta-lactamase but not for a monobactam acyl-enzyme intermediate. Here we used neutron and high-resolution X-ray crystallography to probe the mechanism by which CTX-M extended-spectrum beta-lactamases hydrolyze monobactam antibiotics. In these first reported structures of a class A beta-lactamase in an acyl-enzyme complex with aztreonam, we directly observed most of the hydrogen atoms (as deuterium) within the active site. Although Lys 234 is fully protonated in the acyl intermediate, we found that Lys 73 is neutral. These findings are consistent with Lys 73 being able to serve as a general base during the acylation part of the catalytic mechanism, as previously proposed.
PDB ID: 5KSCDownload
MMDB ID: 144769
PDB Deposition Date: 2016/7/8
Updated in MMDB: 2016/11
Experimental Method:
neutron diffraction
Resolution: 2.1  Å
Source Organism:
Similar Structures:
Biological Unit for 5KSC: monomeric; determined by software (PISA)
Molecular Components in 5KSC
Label Count Molecule
Protein (1 molecule)
Beta-lactamase Toho-1
Molecule annotation
Chemical (1 molecule)
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Citing MMDB