Study identifies histidine ‘pendulum’ mechanism underlying high activity of Group A [FeFe]-hydrogenases

Researchers at Ruhr University Bochum reported that a histidine-mediated, pendulum-like proton-transport mechanism is associated with the high catalytic activity of Group A [FeFe]-hydrogenases. The experimental study, published in the Journal of the American Chemical Society, examined hydrogen production, zinc inhibition and the movement of protons within the enzyme using protein crystallography, hydrogen-production tests, electrochemistry and molecular simulations.

The team found that zinc and other metal ions bound to several sites on [FeFe]-hydrogenases, but only one specific binding location produced inhibition. That site is near the enzyme’s previously known proton-transport pathway. Zinc can also bind non-specifically to sites required for proton binding, but the study’s results point to a particular interaction with two surface histidines as the inhibitory mechanism.

Replacing one of the two histidines with another amino acid left the [FeFe]-hydrogenase highly active but made it insensitive to zinc. Replacing the other histidine reduced hydrogen production to a very slow rate. Together, the experimental results and molecular simulations support a model in which one histidine acts as a movable proton relay: it can receive a proton from the other histidine at the enzyme’s surface and transfer it toward the established proton-transport pathway when oriented inward. Close analysis of crystal structures also identified another amino acid that appears to provide a fixed fulcrum for this movement. The study therefore supports the proposed mechanism, rather than directly observing every step of proton movement in real time.

The researchers also looked for the arrangement in other groups of [FeFe]-hydrogenases and reported that it appeared to be present only in Group A, the group associated with particularly high hydrogen-production rates. They proposed that the two histidines may enable the rapid proton capture linked to this high activity and that the arrangement could have contributed to the evolutionary specialization of Group A hydrogenases. The reported experiments do not establish that evolutionary history or show that this mechanism alone explains the activity difference. The work focuses on molecular function, metal-ion inhibition and proton transport in the enzyme; it does not demonstrate improved hydrogen production in human cells or an industrial process.

Subject of Research: Molecular mechanisms of proton transport and metal-ion inhibition in [FeFe]-hydrogenases

Article Title: A molecular pendulum for efficient hydrogen production

Article References: A molecular pendulum for efficient hydrogen production. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: [FeFe]-hydrogenases, histidine, proton transport, zinc inhibition, protein crystallography, electrochemistry, molecular simulations, hydrogen production, Group A hydrogenases, Ruhr University Bochum, molecular, pendulum