Structural and Functional Analysis of PucM, a Hydrolase in the Ureide Pathway and a Member of the Transthyretin-Related Protein Family

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 103; no. 26; pp. 9790 - 9795
• Main Authors: Jung, Du-Kyo, Lee, Youra, Park, Sung Goo, Park, Byoung Chul, Kim, Ghyung-Hwa, Rhee, Sangkee
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 27.06.2006; National Acad Sciences
• Subjects: Active sites; Amino Acid Sequence; Amino acids; Analysis; Bacillus subtilis; Bacillus subtilis - enzymology; Bacteria; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Binding Sites; Biochemistry; Biological Sciences; Catalysis; Conserved Sequence; Crystallography, X-Ray; Hydrogen bonds; Hydrolases - chemistry; Hydrolases - genetics; Hydrolysis; Ligands; Molecular Sequence Data; Molecules; Monomers; Mutation; Protein Conformation; Proteins; Purines; Structure-Activity Relationship; Symmetry; Uracil - analogs & derivatives; Uracil - chemistry; Uric Acid - analogs & derivatives; Uric Acid - metabolism; Xanthines - chemistry
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0600523103

The ureide pathway, which produces ureides from uric acid, is an essential purine catabolic process for storing and transporting the nitrogen fixed in leguminous plants and some bacteria. PucM from Bacillus subtilis was recently characterized and found to catalyze the second reaction of the pathway, hydrolyzing 5hydroxyisourate (HIU), a product of uricase in the first step. PucM has 121 amino acid residues and shows high sequence similarity to the functionally unrelated protein transthyretin (TTR), a thyroid hormone-binding protein. Therefore, PucM belongs to the TTRrelated proteins (TRP) family. The crystal structures of PucM at 2.0 Å and its complexes with the substrate analogs 8-azaxanthine and 5,6-diaminouracil reveal that even with their overall structure similarity, homotetrameric PucM and TTR are completely different, both in their electrostatic potential and in the size of the active sites located at the dimeric interface. Nevertheless, the absolutely conserved residues across the TRP family, including His-14, Arg-49, His-105, and the C-terminal Tyr-118-Arg-119-Gly-120-Ser-121, indeed form the active site of PucM. Based on the results of site-directed mutagenesis of these residues, we propose a possible mechanism for HIU hydrolysis. The PucM structure determined for the TRP family leads to the conclusion that diverse members of the TRP family would function similarly to PucM as HIU hydrolase.