title: Insight into the catalytic mechanism of arginine deiminase: functional studies on the crucial sites.
abstract: Arginine deiminase (ADI) catalyzes the irreversible hydrolysis of arginine to citrulline and ammonia. It belongs to a newly classified superfamily of guanidino-group-modifying enzymes. Located in the catalytic center of Mycoplasma hominis ADI, some crucial sites (Asp160, Glu212, His268, and Asp270) are highly conserved among these enzymes. Here, we constructed five ADI single mutants D160E, E212D, H268F, H268Y, and D270E, and three double mutants D160E/D270E, D160E/E212D, and E212D/D270E, aiming to evaluate the contributions of these crucial residues to the structure, stability, and enzymatic activity of ADI, and to elucidate their roles in the catalytic process of this family of enzymes. Tryptophan emission fluorescence and circular dichroism were used to analyze the different effects of mutagenesis on these conserved residues on the secondary and tertiary structures of ADI. Urea-induced unfolding and trypsin digestion were applied to measure their stabilities against denaturants and proteases, respectively. Additionally, the enzymatic activities of ADI and its mutants were measured. Here, we report that all the mutations have little effect on the native structure of ADI. However, the substitutions on these crucial sites still interfere with the stability of ADI to different degrees. As these mutations impair both the substrate binding and the substrate induced conformational changes of ADI to different extents, most of the mutants except D160E (preserves about 30% of the enzymatic activity of wild type) have totally lost the enzymatic activity in the hydrolysis of arginine and the inhibitory ability on the proliferation of mouse melanoma cells.
authors.affiliation: Protein Science Laboratory of the Ministry of Education, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, China.
authors.forename: Yunzhou
authors.initials: Y
authors.lastname: Wei
authors.forename: Hao
authors.initials: H
authors.lastname: Zhou
authors.forename: Yi
authors.initials: Y
authors.lastname: Sun
authors.forename: Yingbo
authors.initials: Y
authors.lastname: He
authors.forename: Yongzhang
authors.initials: Y
authors.lastname: Luo
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002384:Catalysis; D002942:Circular Dichroism; D006867:Hydrolases / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D019535:Mycoplasma hominis / Q000201:enzymology; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence
chemical_list: D001426:Bacterial Proteins; D006867:Hydrolases; C019723:arginine deiminase