Alcohol Dehydrogenase D From Pyrococcus furiosus is a Thermostable Rare Earth Element Binding Enzyme: Metal/cofactor Interactions Modulate the Apparent Reaction Equilibrium Constant.

Metals are frequently exploited in the active sites of enzymes; however, the involvement of rare earth elements (REEs) in biocatalysis has been less commonly observed. Here, we show that the alcohol dehydrogenase D (AdhD) from Pyrococcus furiosus can bind REE ions, and the forward activity (alcohol oxidation) is accelerated by the addition of REEs, while, unexpectedly, the reverse reaction is inhibited. In the companion paper, we discovered a REE binding site in the AdhD structure that is distal to the active site. Here, we identified a second REE binding interaction that is only observed in the presence of bound cofactor. The addition of REEs affects the observed equilibrium constant of the reaction, and the binding of the REEs by the enzyme/cofactor complex depends on the redox state of the cofactor. Comparable REE-dependent modulation of catalysis was also observed with human aldose reductase (hAR), suggesting a conserved mechanism of REE interaction among aldo-keto reductase (AKR) family enzymes. REE interactions attenuate the formation of the enzyme cofactor/complexes, which explains the differential impact on the reaction rates and the variable effective reaction equilibrium constant. Together, these results establish a mechanism by which REEs tune catalytic directionality and apparent thermodynamic set points through cofactor-dependent binding and linkage effects, rather than through classical active-site metal catalysis.