Neutron and X-ray crystal structures of a perdeuterated enzyme inhibitor complex reveal the catalytic proton network of the Toho-1 ?-lactamase for the acylation reaction.

ABSTRACT: The mechanism by which class A ?-lactamases hydrolyze ?-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 ?-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 ?-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.

SUBMITTER: Tomanicek SJ 

PROVIDER: S-EPMC3576076 | biostudies-literature | 2013 Feb

REPOSITORIES: biostudies-literature