Crystal structures representing the Michaelis complex and the thiouronium reaction intermediate of Pseudomonas aeruginosa arginine deiminase.

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TitleCrystal structures representing the Michaelis complex and the thiouronium reaction intermediate of Pseudomonas aeruginosa arginine deiminase.
Publication TypeJournal Article
Year of Publication2005
AuthorsGalkin, A, Lu, X, Dunaway-Mariano, D, Herzberg, O
JournalJ Biol Chem
Volume280
Issue40
Pagination34080-7
Date Published2005 Oct 7
ISSN0021-9258
KeywordsApoenzymes, Arginine, Catalytic Domain, Crystallization, Guanidine, Hydrolases, Hydrolysis, Kinetics, Macromolecular Substances, Protein Conformation, Protons, Pseudomonas aeruginosa, Substrate Specificity
Abstract

L-arginine deiminase (ADI) catalyzes the irreversible hydrolysis of L-arginine to citrulline and ammonia. In a previous report of the structure of apoADI from Pseudomonas aeruginosa, the four residues that form the catalytic motif were identified as Cys406, His278, Asp280, and Asp166. The function of Cys406 in nucleophilic catalysis has been demonstrated by transient kinetic studies. In this study, the structure of the C406A mutant in complex with L-arginine is reported to provide a snapshot of the enzyme.substrate complex. Through the comparison of the structures of apoenzyme and substrate-bound enzyme, a substrate-induced conformational transition, which might play an important role in activity regulation, was discovered. Furthermore, the position of the guanidinium group of the bound substrate relative to the side chains of His278, Asp280, and Asp166 indicated that these residues mediate multiple proton transfers. His278 and Asp280, which are positioned to activate the water nucleophile in the hydrolysis of the S-alkylthiouronium intermediate, were replaced with alanine to stabilize the intermediate for structure determination. The structures determined for the H278A and D280A mutants co-crystallized with L-arginine provide a snapshot of the S-alkylthiouronium adduct formed by attack of Cys406 on the guanidinium carbon of L-arginine followed by the elimination of ammonia. Asp280 and Asp166 engage in ionic interactions with the guanidinium group in the C406A ADI. L-arginine structure and might orient the reaction center and participate in proton transfer. Structure determination of D166A revealed the apoD166A ADI. The collection of structures is interpreted in the context of recent biochemical data to propose a model for ADI substrate recognition and catalysis.

DOI10.1074/jbc.M505471200
Alternate JournalJ. Biol. Chem.
PubMed ID16091358
Grant ListP01 GM57890 / GM / NIGMS NIH HHS / United States
R01 AI59733 / AI / NIAID NIH HHS / United States
R01 GM28688 / GM / NIGMS NIH HHS / United States