Primary Citation of Related Structures: 4F8B, 4FGC
PubMed Abstract:
The enzyme QueF catalyzes the reduction of the nitrile group of 7-cyano-7-deazaguanine (preQ(0)) to 7-aminomethyl-7-deazaguanine (preQ(1)), the only nitrile reduction reaction known in biology. We describe here two crystal structures of Bacillus subtilis QueF, one of the wild-type enzyme in complex with the substrate preQ(0), trapped as a covalent thioimide, a putative intermediate in the reaction, and the second of the C55A mutant in complex with the substrate preQ(0) bound noncovalently ...
The enzyme QueF catalyzes the reduction of the nitrile group of 7-cyano-7-deazaguanine (preQ(0)) to 7-aminomethyl-7-deazaguanine (preQ(1)), the only nitrile reduction reaction known in biology. We describe here two crystal structures of Bacillus subtilis QueF, one of the wild-type enzyme in complex with the substrate preQ(0), trapped as a covalent thioimide, a putative intermediate in the reaction, and the second of the C55A mutant in complex with the substrate preQ(0) bound noncovalently. The QueF enzyme forms an asymmetric tunnel-fold homodecamer of two head-to-head facing pentameric subunits, harboring 10 active sites at the intersubunit interfaces. In both structures, a preQ(0) molecule is bound at eight sites, and in the wild-type enzyme, it forms a thioimide covalent linkage to the catalytic residue Cys-55. Both structural and transient kinetic data show that preQ(0) binding, not thioimide formation, induces a large conformational change in and closure of the active site. Based on these data, we propose a mechanism for the activation of the Cys-55 nucleophile and subsequent hydride transfer.
Organizational Affiliation:
Department of Chemistry, Portland State University, Portland, OR 97207, USA.
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