Enzyme Engineering Breakthrough to Revolutionize Steel Industry

Abstract

Ni-Fe carbon monoxide dehydrogenases (CODHs) are nearly diffusion-limited biocatalysts that oxidize CO. Their O2 sensitivity, however, is a major drawback for industrial applications. Here we compare the structures of a fast CODH with a high O2 sensitivity (ChCODH-II) and a slower CODH with a lower O2 sensitivity (ChCODH-IV) (Ch, Carboxydothermus hydrogenoformans). Some variants obtained by simple point mutations of the bottleneck residue (A559) in the gas tunnel showed 61-148-fold decreases in O2 sensitivity while maintaining high turnover rates. The variant structure A559W showed obstruction of one gas tunnel, and molecular dynamics supported the locked position of the mutated side chain in the tunnel. The variant was exposed to different gas mixtures, from simple synthetic gas to sophisticated real flue from a steel mill. Its catalytic properties remained unchanged, even at high O2 levels, and the efficiency was maintained for multiple cycles of CO detoxification/regeneration.

A joint research team, led by Professor Yong Hong Kim and Dr. Suk Min Kim in the Department of Energy and Chemical Engineering and the Graduate School of Carbon Neutrality at UNIST, along with Professor Hyung Ho Lee from the Department of Chemistry at Seoul National University, has achieved a groundbreaking advancement in enzyme engineering. Their research focuses on redesigning Ni-Fe carbon monoxide dehydrogenases (CODHs) to overcome the challenge of oxygen (O2) sensitivity, a critical limitation in industrial applications.

Figure 1. Tunnel-redesigned CO dehydrogenase. Substituting one residue in a predicted tunnel within CO dehydrogenase-II from Carboxydothermus hydrogenoformans (ChCODH-II) from Ala to Trp can decrease its O2 sensitivity without altering overall catalytic activity.

The team's innovative approach involved comparing the structures of two CODH variants: the fast CODH with high O2 sensitivity, ChCODH-II, and the slower CODH with lower O2 sensitivity, ChCODH-IV (Ch, Carboxydothermus hydrogenoformans). Through this comparative analysis, they identified crucial bottleneck residues and successfully engineered a variant (A559W) with significantly reduced O2 sensitivity while maintaining high turnover rates. Molecular dynamics simulations supported their findings, revealing obstruction in a gas tunnel due to a locked position of the mutated side chain.

The engineered enzyme demonstrated remarkable stability and efficiency when exposed to various gas mixtures, including high O2 levels, synthetic gas, and real flue gas from a steel mill. This breakthrough paves the way for utilizing residual carbon-rich gases, such as CO, from the steel industry without the need for prior treatment.

Furthermore, the developed enzyme was successfully employed in the CO hydration reaction, leading to the large-scale production of formic acid. This achievement opens up new possibilities for utilizing not only steel industry by-products, but also gases from coal and plastic waste as valuable resources.

Professor Kim highlighted the practical validation of the enzyme at Hyundai Steel and POSCO sites, emphasizing its potential to advance steel decarbonization initiatives. He stated, "The developed enzyme has undergone direct validation at the facilities of Hyundai Steel and POSCO," highlighting its role in driving steel decarbonization efforts.

Supported by the C1 Gas Refinery Program and the Engineering Research Center Program through the Society of Science and ICT (MSIT) and the National Research Foundation of Korea (NRF), this research has garnered recognition in prestigious publications. The findings have been featured on the cover of Nature Catalysis, as well as highlighted in Nature and featured in a collection in Nature Chemical Engineering in 2022 and 2023, respectively.

Journal Reference

Suk Min Kim, Jinhee Lee, Sung Heuck Kang, et al., "O2-tolerant CO dehydrogenase via tunnel redesign for the removal of CO from industrial flue gas," Nat. Catal., (2024).