Epoxyqueuosine Reductase Structure suggests a Mechanism for Cobalamin-dependent tRNA Modification

DOI: 10.1074/jbc.M115.685693
PMID: 26378237

Authors: Karl Payne (University of Manchester) , Karl Fisher (Manchester Institute of Biotechnology) , Hanno Sjuts (University of Manchester) , Mark Dunstan (University of Manchester) , Bruno Bellina (University of Manchester) , Linus Johannissen (University of Manchester) , Perdita Barran (University of Manchester) , Sam Hay (University of Manchester) , Stephen E.j. Rigby (University of Manchester) , David Leys (School of Chemistry & Manchester Interdisciplinary Biocentre, The University of Manchester)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Biological Chemistry

State: Published (Approved)
Published: September 2015
Diamond Proposal Number(s): 8997 , 12788

Abstract: Queuosine (Q) is a hypermodified RNA base that replaces guanine in the wobble positions of 5prime-GUN-3prime 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 harbours 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 reveal an unexpected diversity in the reductive chemistry catalyzed by these enzymes.

Journal Keywords: Crystal Structure; Electron Paramagnetic Resonance (Epr); Enzyme Mechanism; Nucleic Acid Enzymology; Rna Modification; Transfer Rna (Trna); Iron Sulphur Protein

Subject Areas: Biology and Bio-materials


Instruments: I03-Macromolecular Crystallography