Spectroscopic and Computational Investigation of the Epoxyqueuosine Reductase QueG Reveals Intriguing Similarities with the Reductive Dehalogenase PceA.

Queuosine (Q) is a highly modified nucleoside of transfer RNA that is formed from guanosine triphosphate over the course of eight steps. The final step in this process, involving the conversion of epoxyqueuosine (oQ) to Q, is catalyzed by the enzyme QueG. A recent X-ray crystallographic study revealed that QueG possesses the same cofactors as reductive dehalogenases, including a base-off Co(II)cobalamin (Co(II)Cbl) species and two [4Fe-4S] clusters.

A Spectroscopically Validated Computational Investigation of Viable Reaction Intermediates in the Catalytic Cycle of the Reductive Dehalogenase PceA.

Organisms that produce reductive dehalogenases utilize halogenated aromatic and aliphatic substances as terminal electron acceptors in a process termed organohalide respiration. These organisms can couple the reduction of halogenated substances with the production of ATP. Tetrachloroethylene reductive dehalogenase (PceA) catalyzes the reductive dehalogenation of per- and trichloroethylenes (PCE and TCE, respectively) to primarily -dichloroethylene (DCE).

Chlorocob(II)alamin Formation Which Enhances the Thiol Oxidase Activity of the B-Trafficking Protein CblC.

CblC is a chaperone that catalyzes removal of the β-axial ligand of cobalamin (or B), generating cob(II)alamin in an early step in the cofactor trafficking pathway. Cob(II)alamin is subsequently partitioned to support cellular needs for the synthesis of active cobalamin cofactor derivatives. In addition to the β-ligand transferase activity, the CblC (CblC) and clinical R161G/Q variants of the human protein exhibit robust thiol oxidase activity, converting glutathione to glutathione disulfide while concomitantly reducing O to HO.