Carbon monoxide dehydrogenase (CODH)-catalyzed oxidation of CO to CO 2 provides a promising means of removal of toxic and waste CO from industrial ue gas despite of the lack of active and stable enzymes in the atmosphere. Herein we present rationally and selectively redesigned ChCODH-II (Carboxydothermus hydrogenoformans) variants by engineering gas tunnels in order for O 2 -tolerant CODHs to catalyze e cient CO oxidation under oxygen (O 2 ). Using the redesigned ChCODH-II A559W and A559H variants showing 42-and 128-fold elevation of O 2 tolerance, respectively, complete CO removal was achieved under a near-atmospheric condition. Moreover, these variants e ciently removed CO from industrial ue gas (Linz-Donawiz converter Gas: LDG) discharged from a steel mill despite the high O 2 level (13.4%) during successful and repeated reuse after immobilized on Ni-NTA agarose beads. Our study will provide insights into redesigning the transformation of O 2 -sensitive CODHs into tolerant enzymes for use as workhorses for conversion of toxic or waste gases into safe or value-added chemicals.
MainLarge amounts of CO pollutants are emitted from natural sources as well as man-made processes 1 (e.g. annually over 219 billion Nm 3 of CO-containing ue gases from POSCO) 2,3 . Carbon monoxide (CO), the most abundant air pollutant found in the atmosphere other than CO 2 according to the OECD database (https://stats.oecd.org, air emissions source in 2017), can provide su cient carbon and energy sources for converting waste gas to fuels and chemicals through a clean and sustainable method. To convert
Fe‒S cluster-harboring enzymes, such as carbon monoxide dehydrogenases (CODH), employ sophisticated artificial electron mediators like viologens to serve as potent biocatalysts capable of cleaning-up industrial off-gases at stunning reaction rates. Unraveling the interplay between these enzymes and their associated mediators is essential for improving the efficiency of CODHs. Here we show the electron mediator-interaction site on ChCODHs (Ch, Carboxydothermus hydrogenoformans) using a systematic approach that leverages the viologen-reactive characteristics of superficial aromatic residues. By enhancing mediator-interaction (R57G/N59L) near the D-cluster, the strategically tailored variants exhibited a ten-fold increase in ethyl viologen affinity relative to the wild-type without sacrificing the turn-over rate (kcat). Viologen-complexed structures revealed the pivotal positions of surface phenylalanine residues, serving as external conduits for the D-cluster. One variant (G57/L59/W559) could treat a broad spectrum of waste gases (from steel-process and plastic-gasification) containing O2. Decoding mediator interactions will facilitate the development of industrially high-efficient biocatalysts encompassing gas-utilizing enzymes.
Carbon monoxide dehydrogenase (CODH)-catalyzed oxidation of CO to CO2 provides a promising means of removal of toxic and waste CO from industrial flue gas despite of the lack of active and stable enzymes in the atmosphere. Herein we present rationally and selectively redesigned ChCODH-II (Carboxydothermus hydrogenoformans) variants by engineering gas tunnels in order for O2-tolerant CODHs to catalyze efficient CO oxidation under oxygen (O2). Using the redesigned ChCODH-II A559W and A559H variants showing 42- and 128-fold elevation of O2 tolerance, respectively, complete CO removal was achieved under a near-atmospheric condition. Moreover, these variants efficiently removed CO from industrial flue gas (Linz–Donawiz converter Gas: LDG) discharged from a steel mill despite the high O2 level (13.4%) during successful and repeated reuse after immobilized on Ni-NTA agarose beads. Our study will provide insights into redesigning the transformation of O2-sensitive CODHs into tolerant enzymes for use as workhorses for conversion of toxic or waste gases into safe or value-added chemicals.
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