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hox and hyp operon

Introduction

The Ni-Fe hydrogenase we use is an enzyme that functions in vivo bidirectionally for NAD⁺ reduction and NADH oxidation coupled to H₂ uptake and H₂ production, respectively. ^[1] In our design, the Ni-Fe hydrogenase works mainly to restore the nickel to a zero valence, which can help reduce nickel toxicity and collect nickel particles.

Usage and Biology

The Ni-Fe hydrogenase is made up of six major and three auxiliary subunits. The former includes hoxF, hoxU, hoxY, hoxH, hoxW and hoxI, while the latter includes hypA, hypB and hypF.

The hoxF and the hoxU form the module of NADH dehydrogenase. The hoxF is a hydrogenase subunit responsible for electron transport. The most important group in hoxF is FMN-b, which has the ability of switching electron. Under anaerobic conditions, NADH is oxidized to NAD⁺ on the surface of hoxF subunit. In the meanwhile, the electrons generated in this reaction travel through a series of processes to the hoxH, completing the reduction of the hydrogen ion. Under aerobic conditions, NAD⁺ is reduced to NADH on the surface of the hoxF subunit. The electron transferring is contrary to former. ^[2] The hoxU houses a 2Fe-2S cluster and is responsible for the role of conducting electrons between hoxH and hoxF. ^[3]

The hoxY and the hoxH form the module of catalytic center.The hoxY houses a [4Fe-4S] cluster of the site, and an FMN group (FMN-a) near the Ni-Fe site in the hoxH. ^[4] The most important site in hoxH is the [NiFe] -hydrogenase active site, which is composed of nickel and iron coordinated with cysteine residues, cyanide and carbon monoxide. ^[5] It is the most central component of our intracellular conversion of nickel ions.

Characterization

Sequence and Features

References

1. ↑ Teramoto, H., Shimizu, T., Suda, M., & Inui, M. (2022). Hydrogen production based on the heterologous expression of NAD+-reducing [NiFe]-hydrogenase from Cupriavidus necator in different genetic backgrounds of Escherichia coli strains. International Journal of Hydrogen Energy, 47(52), 22010–22021.
2. ↑ Löscher, S., Burgdorf, T., Zebger, I., Hildebrandt, P., Dau, H., Friedrich, B., & Haumann, M. (2006). Bias from H2 Cleavage to Production and Coordination Changes at the Ni−Fe Active Site in the NAD+-Reducing Hydrogenase from Ralstonia eutropha. Biochemistry, 45(38), 11658–11665.
3. ↑ Löscher, S., Burgdorf, T., Zebger, I., Hildebrandt, P., Dau, H., Friedrich, B., & Haumann, M. (2006). Bias from H2 Cleavage to Production and Coordination Changes at the Ni−Fe Active Site in the NAD+-Reducing Hydrogenase from Ralstonia eutropha. Biochemistry, 45(38), 11658–11665.
4. ↑ Löscher, S., Burgdorf, T., Zebger, I., Hildebrandt, P., Dau, H., Friedrich, B., & Haumann, M. (2006). Bias from H2 Cleavage to Production and Coordination Changes at the Ni−Fe Active Site in the NAD+-Reducing Hydrogenase from Ralstonia eutropha. Biochemistry, 45(38), 11658–11665.
5. ↑ Chan, K.-H., Lee, K.-M., & Wong, K.-B. (2012). Interaction between Hydrogenase Maturation Factors HypA and HypB Is Required for [NiFe]-Hydrogenase Maturation. PLOS ONE, 7(2), e32592.