Epoxyqueuosine Reductase Structure Suggests a Mechanism for Cobalamin-dependent tRNA Modification
| Autor: | Karl Fisher, Stephen E. J. Rigby, Linus O. Johannissen, Mark S. Dunstan, David Leys, Sam Hay, Karl A. P. Payne, Hanno Sjuts, Perdita E. Barran, Bruno Bellina |
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| Rok vydání: | 2015 |
| Předmět: |
TRNA modification
crystal structure Halogenation Stereochemistry Molecular Sequence Data Queuosine Crystallography X-Ray Biochemistry Catalysis Protein Structure Secondary 03 medical and health sciences chemistry.chemical_compound RNA Transfer Nucleoside Q Streptococcus thermophilus iron sulfur protein enzyme mechanism Amino Acid Sequence Molecular Biology 030304 developmental biology Dehalogenase 0303 health sciences biology 030302 biochemistry & molecular biology nucleic acid enzymology Leaving group Active site Queuine Cell Biology Cobalt vitamin B12 queuosine biosynthesis RNA modification Solutions Vitamin B 12 electron paramagnetic resonance (EPR) transfer RNA (tRNA) chemistry Transfer RNA biology.protein Enzymology Oxidoreductases Oxidation-Reduction |
| Zdroj: | The Journal of Biological Chemistry |
| ISSN: | 1083-351X |
| Popis: | Background: Little is known about epoxyqueuosine reductase (QueG), which catalyzes the final step in the biosynthesis of queuosine. Results: We report solution and structural characterization of Streptococcus thermophilus QueG. Conclusion: The QueG similarity to reductive dehalogenases is largely limited to cofactor binding. Significance: Our study establishes the link between cobalamin-metabolism and tRNA modification and suggests a mechanism for cobalamin-dependent epoxide reduction. Queuosine (Q) is a hypermodified RNA base that replaces guanine in the wobble positions of 5′-GUN-3′ tRNA molecules. Q is exclusively made by bacteria, and the corresponding queuine base is a micronutrient salvaged by eukaryotic species. The final step in Q biosynthesis is the reduction of the epoxide precursor, epoxyqueuosine, to yield the Q cyclopentene ring. The epoxyqueuosine reductase responsible, QueG, shares distant homology with the cobalamin-dependent reductive dehalogenase (RdhA), however the role played by cobalamin in QueG catalysis has remained elusive. We report the solution and structural characterization of Streptococcus thermophilus QueG, revealing the enzyme harbors a redox chain consisting of two [4Fe-4S] clusters and a cob(II)alamin in the base-off form, similar to RdhAs. In contrast to the shared redox chain architecture, the QueG active site shares little homology with RdhA, with the notable exception of a conserved Tyr that is proposed to function as a proton donor during reductive dehalogenation. Docking of an epoxyqueuosine substrate suggests the QueG active site places the substrate cyclopentane moiety in close proximity of the cobalt. Both the Tyr and a conserved Asp are implicated as proton donors to the epoxide leaving group. This suggests that, in contrast to the unusual carbon-halogen bond chemistry catalyzed by RdhAs, QueG acts via Co-C bond formation. Our study establishes the common features of Class III cobalamin-dependent enzymes, and reveals an unexpected diversity in the reductive chemistry catalyzed by these enzymes. |
| Databáze: | OpenAIRE |
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