Neutron and X-Ray Crystal Structures of a Perdeuterated Enzyme Inhibitor Complex Reveal the Catalytic Proton Network of the Toho-1 Beta-Lactamase for the Acylation Reaction.Tomanicek, S.J., Standaert, R.F., Weiss, K.L., Ostermann, A., Schrader, T.E., Ng, J.D., Coates, L.
(2013) J.Biol.Chem. 288: 4715
- PubMed: 23255594
- DOI: 10.1074/jbc.M112.436238
- Primary Citation of Related Structures:  4BD0
- PubMed 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 diffra ...
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.
Oak Ridge National Laboratory, OakRidge, Tennessee 37831, USA.