Dataset Information

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

ABSTRACT: 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. While the initial step in the catalytic cycle of QueG likely involves the formation of a reduced Co(I)Cbl species, the mechanisms employed by this enzyme to accomplish the thermodynamically challenging reduction of base-off Co(II)Cbl to Co(I)Cbl and to convert oQ to Q remain unknown. In this study, we have used electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopies in conjunction with whole-protein quantum mechanics/molecular mechanics (QM/MM) computations to further characterize wild-type QueG and select variants. Our data indicate that the Co(II)Cbl cofactor remains five-coordinate upon substrate binding to QueG. Notably, during a QM/MM optimization of a putative QueG reaction intermediate featuring an alkyl-Co(III) species, the distance between the Co ion and coordinating C atom of oQ increased to >3.3 Å and the C-O bond of the epoxide reformed to regenerate the oQ-bound Co(I)Cbl reactant state of QueG. Thus, our computations indicate that the QueG mechanism likely involves single-electron transfer from the transient Co(I)Cbl species to oQ rather than direct Co-C bond formation, similar to the mechanism that has recently been proposed for the tetrachloroethylene reductive dehalogenase PceA.

SUBMITTER: Greenhalgh ED

PROVIDER: S-EPMC8935625 | biostudies-literature | 2022 Feb

REPOSITORIES: biostudies-literature

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

Greenhalgh Elizabeth D ED Kincannon William W Bandarian Vahe V Brunold Thomas C TC

Biochemistry 20220121 3

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. While the initial step in the catalytic cycle ...[more]

PMID: 35061353

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Project description:Reductive dehalogenases (RDases) are essential in the anaerobic degradation of various organohalide contaminants. This family of enzymes has broad sequence diversity, but high structural conservation. There have been few studies assessing how RDase amino acid sequences affect their substrate selectivity. Here, we focus on two chloroalkane RDases, CfrA and DcrA, which have 95% protein sequence identity but have diverged to have opposite substrate preferences. CfrA dechlorinates chloroform (CF) and 1,1,1-trichloroethane (TCA) but not 1,1-dichloroethane (DCA), while DcrA will dechlorinate 1,1-DCA but not CF or 1,1,1-TCA. We mutated several residues in the active site of CfrA to investigate a change in substrate preference and to identify which wild-type residues contribute the most to substrate specialization. We determined that no individual residue solely dictates substrate discrimination, but both Y80W and F125W mutations were needed to force CfrA to prefer 1,1-DCA as a substrate. When using 1,1,2-TCA as a substrate, CfrA predominately performs hydrogenolysis to 1,2-DCA, yet the introduction of the double mutant changed this preference to dihaloelimination (forming vinyl chloride). We use predictive protein models and substrate docking to predict what interactions are made between the enzyme and substrate to aid in selection. The residues of significance identified in this study are consistent with those identified from chloroethene RDases, suggesting residue locations with a particularly high impact on activity.IMPORTANCEReductive dehalogenases (RDases) play an integral role in the removal of chlorinated solvents from the environment. These enzymes have specificity toward different chlorinated compounds, and it is known that natural variants of highly similar RDases can have distinct activities. How specific differences in protein sequence influence activity is largely unknown. In this study, we demonstrate that mutating a few residues within the active site of CfrA-a chloroform and trichloroethane-specific dehalogenase-changes its substrate preference to dichloroethane. We determine that only two mutations are needed to disrupt the native activity, underscoring the nuances in substrate-structure relationships in RDases. Though we are still far from predicting function from the sequence, this knowledge can give some insight into engineering RDases for new target contaminants.

Dataset Information

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

Publications

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

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