Crystal structure of Bacillus subtilis guanine deaminase: the first domain-swapped structure in the cytidine deaminase superfamily

Guanine deaminase, a key enzyme in the nucleotide metabolism, catalyzes the hydrolytic deamination of guanine into xanthine. The crystal structure of the 156-residue guanine deaminase from Bacillus subtilis has been solved at 1.17-A resolution. Unexpectedly, the C-terminal segment is swapped to form...

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Bibliographic Details
Published in:The Journal of biological chemistry 2004-08, Vol.279 (34), p.35479-35485
Main Authors: Liaw, Shwu-Huey, Chang, Yu-Jui, Lai, Cheng-Tsung, Chang, Hui-Chuan, Chang, Gu-Gang
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Bacillus subtilis
Bacillus subtilis - chemistry
Bacillus subtilis - enzymology
Bacterial Proteins - chemistry
Binding Sites
Crystallography, X-Ray
Cytidine Deaminase - chemistry
Dimerization
Guanine Deaminase - chemistry
Models, Molecular
Molecular Sequence Data
Molecular Structure
Protein Conformation
Protein Folding
Sequence Homology, Amino Acid
Substrate Specificity
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Summary:Guanine deaminase, a key enzyme in the nucleotide metabolism, catalyzes the hydrolytic deamination of guanine into xanthine. The crystal structure of the 156-residue guanine deaminase from Bacillus subtilis has been solved at 1.17-A resolution. Unexpectedly, the C-terminal segment is swapped to form an intersubunit active site and an intertwined dimer with an extensive interface of 3900 A(2) per monomer. The essential zinc ion is ligated by a water molecule together with His(53), Cys(83), and Cys(86). A transition state analog was modeled into the active site cavity based on the tightly bound imidazole and water molecules, allowing identification of the conserved deamination mechanism and specific substrate recognition by Asp(114) and Tyr(156'). The closed conformation also reveals that substrate binding seals the active site entrance, which is controlled by the C-terminal tail. Therefore, the domain swapping has not only facilitated the dimerization but has also ensured specific substrate recognition. Finally, a detailed structural comparison of the cytidine deaminase superfamily illustrates the functional versatility of the divergent active sites found in the guanine, cytosine, and cytidine deaminases and suggests putative specific substrate-interacting residues for other members such as dCMP deaminases.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M405304200