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Structure of N-Formimino-l-glutamate Iminohydrolase from Pseudomonas aeruginosa
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文摘
N-Formimino-mallcaps">l-glutamate iminohydrolase (HutF), from Pseudomonas aeruginosa with a locus tag of Pa5106 (gi|15600299), is a member of the amidohydrolase superfamily. This enzyme catalyzes the deamination of N-formimino-mallcaps">l-glutamate to N-formyl-mallcaps">l-glutamate and ammonia in the histidine degradation pathway. The crystal structure of Pa5106 was determined in the presence of the inhibitors N-formimino-mallcaps">l-aspartate and N-guanidino-mallcaps">l-glutaric acid at resolutions of 1.9 and 1.4 脜, respectively. The structure of an individual subunit is composed of two domains with the larger domain folding as a distorted (尾/伪)8-barrel. The (尾/伪)8-barrel domain is composed of eight 尾-strands flanked by 11 伪-helices, whereas the smaller domain is made up of eight 尾-strands. The active site of Pa5106 contains a single zinc atom that is coordinated by His-56, His-58, His-232, and Asp-320. The nucleophilic solvent water molecule coordinates with the zinc atom at a distance of 2.0 脜 and is hydrogen bonded to Asp-320 and His-269. The 伪-carboxylate groups of both inhibitors are hydrogen bonded to the imidazole moiety of His-206, the hydroxyl group of Tyr-121, and the side chain amide group of Gln-61. The side chain carboxylate groups of the two inhibitors are ion-paired with the guanidino groups of Arg-209 and Arg-82. Computational docking of high-energy tetrahedral intermediate forms of the substrate, N-formimino-mallcaps">l-glutamate, to the three-dimensional structure of Pa5106 suggests that this compound likely undergoes a re-faced nucleophilic attack at the formimino group by the metal-bound hydroxide. A catalytic mechanism of the reaction catalyzed by Pa5106 is proposed.

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