PMID:23255594
| Citation |
Tomanicek, SJ, Standaert, RF, Weiss, KL, Ostermann, A, Schrader, TE, Ng, JD and Coates, L (2013) Neutron and X-ray crystal structures of a perdeuterated enzyme inhibitor complex reveal the catalytic proton network of the Toho-1 β-lactamase for the acylation reaction. J. Biol. Chem. 288:4715-22 |
|---|---|
| Abstract |
The mechanism by which class A β-lactamases hydrolyze β-lactam antibiotics has been the subject of intensive investigation using many different experimental techniques. Here, we report on the novel use of both neutron and high resolution x-ray diffraction to help elucidate the identity of the catalytic base in the acylation part of the catalytic cycle, wherein the β-lactam ring is opened and an acyl-enzyme intermediate forms. To generate protein crystals optimized for neutron diffraction, we produced a perdeuterated form of the Toho-1 β-lactamase R274N/R276N mutant. Protein perdeuteration, which involves replacing all of the hydrogen atoms in a protein with deuterium, gives a much stronger signal in neutron diffraction and enables the positions of individual deuterium atoms to be located. We also synthesized a perdeuterated acylation transition state analog, benzothiophene-2-boronic acid, which was also isotopically enriched with (11)B, as (10)B is a known neutron absorber. Using the neutron diffraction data from the perdeuterated enzyme-inhibitor complex, we were able to determine the positions of deuterium atoms in the active site directly rather than by inference. The neutron diffraction results, along with supporting bond-length analysis from high resolution x-ray diffraction, strongly suggest that Glu-166 acts as the general base during the acylation reaction. |
| Links |
PubMed PMC3576076 Online version:10.1074/jbc.M112.436238 |
| Keywords |
Acylation; Catalysis; Catalytic Domain; Crystallography, X-Ray/methods; Drug Resistance, Bacterial; Enzyme Inhibitors/pharmacology; Escherichia coli/enzymology; Escherichia coli Proteins/chemistry; Hydrogen/chemistry; Hydrogen Bonding; Ligands; Models, Chemical; Molecular Conformation; Neutrons; Nitrogen/chemistry; Protons; Thiophenes/chemistry; beta-Lactamases/chemistry |
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