期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 108, 期 10, 页码 3912-3917出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1019480108
关键词
X-ray crystallography; pulcherrimin; diketopiperazine; divergent evolution; thioesterase domain
资金
- Ministry of Education, Culture, Sports, Science and Technology (MEXT)
- Uehara Memorial Foundation
- Japan Society for the Promotion of Science
- MEXT
Cyclodipeptides are secondary metabolites biosynthesized by many bacteria and exhibit a wide array of biological activities. Recently, a new class of small proteins, named cyclodipeptide synthases (CDPS), which are unrelated to the typical nonribosomal peptide synthetases, was shown to generate several cyclodipeptides, using aminoacyl-tRNAs as substrates. The Mycobacterium tuberculosis CDPS, Rv2275, was found to generate cyclodityrosine through the formation of an aminoacyl-enzyme intermediate and to have a structure and oligomeric state similar to those of the class Ic aminoacyl-tRNA synthetases (aaRSs). However, the poor sequence conservation among CDPSs has raised questions about the architecture and catalytic mechanism of the identified homo-logs. Here we report the crystal structures of Bacillus licheniformis CDPS YvmC-Blic, in the apo form and complexed with substrate mimics, at 1.7-2.4-angstrom resolutions. The YvmC-Blic structure also exhibits similarity to the class Ic aaRSs catalytic domain. Our mutational analysis confirmed the importance of a set of residues for cyclodileucine formation among the conserved residues localized in the catalytic pocket. Our biochemical data indicated that YvmC-Blic binds tRNA and generates cyclodileucine as a monomer. We were also able to detect the presence of an aminoacyl-enzyme reaction intermediate, but not a dipeptide tRNA intermediate, whose existence was postulated for Rv2275. Instead, our results support a sequential catalytic mechanism for YvmC-Blic, with the successive attachment of two leucine residues on the enzyme via a conserved serine residue. Altogether, our findings suggest that all CDPS enzymes share a common aaRS-like architecture and a catalytic mechanism involving the formation of an enzyme-bound intermediate.
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