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Inhibition of the Type IB GTP Cyclohydrolase (LB262)
Author(s) -
Alvarez Jonathan,
Swairjo Manal
Publication year - 2014
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.28.1_supplement.lb262
Subject(s) - active site , ribose , gtp' , chemistry , stereochemistry , enzyme , nucleoside triphosphate , biochemistry , binding site , nucleoside , nucleotide , gene
The type IB GTP cyclohydrolase (GCYH‐IB) is a tunnel‐fold enzyme that catalyzes the complex conversion of GTP to 7,8‐dihydroneopterin triphosphate in the biosynthesis of folate and the tRNA modified nucleoside queuosine in bacteria. Because it is an essential enzyme in several pathogenic bacteria, and is structurally and functionally distinct from the canonical type IA enzyme (GCYH‐IA) involved in biopterin biosynthesis in humans, GCYH‐IB has been proposed as a potential antibacterial target. Based on lack of sequence homology, different metal dependencies and active site architectures, we propose that the two enzymes utilize the same chemical mechanism but employ different strategies for catalysis. Here we describe the 2.77 Å‐resolution crystal structure of N. gonorrhoeae GCYH‐IB in complex with an 8‐oxoguanine derivative of GTP (8‐oxo‐GTP), a potent competitive inhibitor, and comparative analysis with the ‐IA enzyme in complex with the same inhibitor. The structure reveals a similar mode of binding for the guanine moiety but different modes of binding for the ribose and triphosphate tail. In both enzymes, the O8 atoms of 8‐oxo‐GTP acts as a ligand in the tetrahedral coordination of the catalytic Zn2+ ion. However, three key differences are observed in their interactions with the inhibitor: 1) The water molecule proposed to be the first nucleophile in the GCYH‐IA reaction is absent from the active site of GCYH‐IB. 2) In GCYH‐IB, the ribose hydroxyl groups of 8‐oxo‐GTP are coordinated by two active‐site side chains instead of one. 3) The inhibitor O8 atom is additionally coordinated via a water‐mediated hydrogen bond with a conserved His, an interaction only present in GCYH‐IB. These results explain the different inhibition properties of the two enzymes and confirm that they employ different catalytic strategies.