. Scientific Frontline: A poison helps to understand hydrogen-producing biocatalysts

Friday, December 16, 2022

A poison helps to understand hydrogen-producing biocatalysts

Thomas Happe researches biocatalysts that can produce hydrogen in an environmentally friendly way.
 Photo Credit: RUB, Marquard

The toxic cyanide molecule attacks the enzymes, but also enables new insights into catalysis.

In nature, certain enzymes, so-called hydrogenases, are able to produce molecular hydrogen (H2) to produce. Special types of these biocatalysts, so-called [FeFe] hydrogenases, are extremely efficient and therefore of interest for bio-based hydrogen production. Although science already knows a lot about how these enzymes work, some details have not yet been fully clarified. The photobiotechnology working group at the Ruhr University Bochum around Dr. Jifu Duan and Prof. Dr. Close Thomas Happe. The researchers showed that external cyanide binds to the [FeFe] hydrogenases and inhibits hydrogen formation. They were able to demonstrate a structural change in the proton transport path that helps to understand the coupling of electron and proton transport. They report in the journal Angewandte Chemie.

Sophisticated internal catalyst

To produce hydrogen, biocatalysts transfer electrons to protons, using a sophisticated structure as an internal catalyst. This so-called H cluster contains electronically active iron ions that are bound to what most people know as toxins: carbon monoxide and cyanide. However, although internal carbon monoxide and cyanide are important for the high activity of the hydrogenases, additional external carbon monoxide prevents it when it binds to the H cluster, the H2-Production. "Interestingly, cyanide is also a well-known inhibitor for iron-containing biocatalysts," says Jifu Duan. “However, its effect on [FeFe] hydrogenases have so far hardly been investigated."

The Bochum research team was able to close this gap. The researchers showed that external cyanide also binds to [FeFe] hydrogenases and inhibits them. In collaboration with the Protein Crystallography Working Group of Prof. Dr. Eckhard Hofmann was able to change the structure of H2 dissolve producing biocatalysts to which external cyanide was bound. "The high-resolution structure in combination with spectroscopic analyzes shows us that the external cyanide binds directly to the H cluster, similar to other inhibitors examined so far," says Jifu Duan. “This explains why the hydrogenase is inactive after treatment with cyanide."

Coincidentally recorded a transition state

Thomas Happe, Jifu Duan, Eckhard Hofmann and Anja Hemschemeier stand for the team of authors.
Photo Credit: RUB, Marquard

When the scientists examined the structure of the hydrogenase poisoned with cyanide in more detail, they experienced a surprise: they found structural changes in the proton transport path that are necessary to remove the protons that lead to H2 will lead to the H cluster. “This change was suspected to be crucial for an efficient proton shuttle, but had never been structurally observed. Coincidentally, the cyanide bond helped us to grasp such a transition state,” says Jian Duan. “These findings are important in order to understand the coupling of electron and proton transport, which is not only for H2 producing enzymes, but is also important for many other biocatalysts,” concludes Thomas Happe.

The work was funded by the German Research Foundation, the Volkswagen Foundation and the excellence strategy of the federal and state governments as part of the Cluster of Excellence RESOLV - EXC 2033 (project number 390677874).

Published in journalAngewandte Chemie

Source/CreditRuhr University Bochum

Reference Number: chm121622_01

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