Anja Hemschemeier, Thomas Happe, and Zhaoya Yhang (from left) are part of the team of authors.
Photo Credit: © RUB, Marquard
Scientific Frontline: Extended "At a Glance" Summary: [FeFe]-Hydrogenase Proton Capture Mechanism
The Core Concept: A mechanism used by specific biocatalysts, called [FeFe]-hydrogenases, to rapidly capture and transport protons from their environment to produce hydrogen.
Key Distinction/Mechanism: The process relies on two specific histidine amino acids located on the surface of the enzyme that act like a pendulum, capturing protons from the surrounding cellular fluid and funneling them inward to the catalytic site.
Major Frameworks/Components:
- [FeFe]-hydrogenases: The highly efficient biocatalysts responsible for hydrogen production.
- Histidine residues: The specific amino acids on the enzyme's surface that mediate proton binding and transport.
- Zinc inhibition: The use of zinc binding to identify and block the proton transport pathway, revealing the function of the histidine "pendulum."
Branch of Science: Biochemistry, Biophysics, Electrochemistry, Biotechnology, Evolutionary Biology
Future Application: Understanding this high-efficiency mechanism could lead to the development of synthetic catalysts for sustainable hydrogen fuel production.
Why It Matters: These enzymes can process nearly 10,000 protons per second. Unlocking their exact molecular mechanisms is crucial for bio-inspired engineering and advancing clean energy technologies.
Enzymes that are particularly efficient at producing hydrogen must capture protons from the solvent extremely quickly. Researchers in Bochum have discovered how they accomplish this.
Nearly all metabolic processes require protons—positively charged hydrogen atoms. Although these are abundant in cellular fluid, the biocatalysts involved depend on mechanisms for efficiently capturing protons and transporting them to the site where catalysis occurs. Enzymes from microorganisms can produce hydrogen (H2) by combining electrons with protons. These hydrogenases are so efficient that a single biocatalyst can capture nearly 10,000 protons per second. A team of researchers from the Photobiotechnology group at Ruhr University Bochum, Germany, has discovered how they do this.
How an Inhibitor Can Help Us Understand Biocatalysts
Zinc occurs naturally in many biocatalysts, where it is needed for the reaction mechanism. This metal ion binds to reactive groups of certain molecular components—the amino acids—of the enzyme. “Yet through this same bond, zinc can block biocatalysts,” explains Dr. Jifu Duan, first author of the current study. “It can also bind non-specifically to sites required for proton binding.”
Researchers at Ruhr University Bochum have examined how zinc affects the production of hydrogen by [FeFe]-hydrogenases and made an interesting discovery. “Although we were able to see in crystal structures that zinc binds to various sites of the [FeFe]-hydrogenases, the interaction at only one very specific location resulted in inhibition,” says Duan. Notably, this point is in the direct vicinity of the previously known proton transport pathway of the hydrogenases.
Zinc Blocks a Proton-Transporting Pendulum
The team led by Duan and Professor Thomas Happe demonstrated that the binding of zinc and other metal ions blocks very specific amino acids, namely two histidines on the surface of [FeFe]-hydrogenases. Histidines in enzymes are known for binding protons, but their role in [FeFe]-hydrogenases was previously unexplored. When the researchers replaced one of these histidines with another amino acid, the biocatalyst remained highly active but became insensitive to zinc. However, when they replaced the other histidine, the [FeFe]-hydrogenase could only produce hydrogen very slowly.
Using various methods—protein crystallography, hydrogen production tests, electrochemistry, and molecular simulations—the team demonstrated that one of these two histidines forms a molecular pendulum. When it swings to the surface of the enzyme, it can receive a proton from the other histidine; when it swings toward the interior of the enzyme, it transfers the proton to a known proton transport pathway. This pendulum also has a fixed fulcrum, which is another amino acid that the researchers only noticed by closely analyzing the crystal structures.
Has the Evolution of the Protein Pendulum Led to Particularly Efficient Hydrogenases?
Today, researchers are aware of many different groups of [FeFe]-hydrogenases, but only those in Group A appear to achieve the particularly high production rates that make these biocatalysts so exciting and of interest for biotechnological applications. “We looked for our pendulum in other groups of [FeFe]-hydrogenases as well, but it appears to be only present in Group A,” says Happe. “We believe that the two histidines are responsible for their swift capture of protons, and thus their high level of activity.”
In the course of evolution, this mechanism could have led to the specialization of this group of hydrogenases. This insight could help to better understand the molecular mechanisms of other hydrogenases and, perhaps, develop biocatalysts that are better suited for bio-based industrial processes. However, the results are also important for understanding the H2 metabolism in living organisms, which plays an important role in many ecosystems.
Funding: The work was supported by the German Research Foundation through individual funding, the Research Training Group MiCon, and the Excellence Cluster RESOLV.
Published in journal: Journal of the American Chemical Society
Authors: Jifu Duan, Zhaoya Yang, Oliver Lampret, Federica Arrigoni, Lukas van Impel, Feng Zheng, Julian Kleinhaus, Ulf-Peter Apfel, Claudio Greco, Luca De Gioia, Eckhard Hofmann, Anja Hemschemeier, and Thomas Happe
Source/Credit: Ruhr-Universität Bochum | Thomas Happe and Meike Drießen
Edited by: Scientific Frontline
Reference Number: bchm101926_01
