Bridged or not? Scientists uncover a key step in hydrogenase assembly

June 1, 2026 dialog Bridged or not? Scientists uncover a key step in hydrogenase assembly Lisa Lock Scientific Editor Robert Egan Associate Editor How does nature build one of the most sophisticated catalytic metal centers found in biology? An international team of researchers has now resolved a long-standing debate surrounding the assembly of the active site of [FeFe]-hydrogenases—enzymes that rank among nature's most efficient catalysts for hydrogen production and consumption. The study, led by scientists within the "UniSysCat" research network at the Technical University of Berlin and Uppsala University, combined advanced synchrotron spectroscopy with artificial intelligence-based structural modeling to investigate how a protein called HydF helps construct the hydrogenase catalytic center. The findings were obtained using the PETRA III synchrotron radiation source at DESY and are published in Angewandte Chemie International Edition. [FeFe]-hydrogenases catalyze the reversible conversion of protons into molecular hydrogen using an iron-based catalytic core. Their remarkable efficiency has attracted attention as a potential blueprint for future hydrogen-based energy technologies. Central to their function is the H-cluster, a unique organometallic cofactor assembled through a complex biosynthetic pathway involving several accessory proteins. One of the key players in this process is HydF, a scaffold protein that temporarily hosts the precursor of the H-cluster before it is transferred to the mature enzyme. For more than a decade, scientists have debated exactly how this precursor interacts with HydF. In particular, some studies suggested that the precursor might form a direct chemical connection to HydF's own iron-sulfur cluster through an unusual cyanide bridge. To test this hypothesis, the researchers employed nuclear resonance vibrational spectroscopy (NRVS) at beamline P01 of PETRA III. By selectively incorporating the iron isotope 57Fe into either the HydF iron-sulfur cluster or the diiron precursor, they were able to observe vibrations originating from specific iron sites within the protein. "The ability to selectively observe vibrations from individual iron centers allowed us to directly test competing models for the HydF maturation mechanism," says Giorgio Caserta of TU Berlin, corresponding author of the study together with Gustav Berggren of Uppsala University. The measurements revealed that although the diiron precursor binds in close proximity to the HydF [4Fe–4S] cluster, the two cofactors are not connected through the proposed Fe–CN–Fe bridge. Instead, they interact through a non-covalent but electronically coupled arrangement. The iron-sulfur cluster appears to play a different role: stabilizing a highly organized binding environment that protects and positions the fragile precursor during assembly. To explore how HydF might participate in even earlier stages of H-cluster biosynthesis, the team complemented the spectroscopic experiments with AI-driven structural predictions using Boltz-2. The models suggest that HydF's iron-sulfur cluster may also help organize interactions with Hmet, a lipoate-containing protein of the glycine cleavage system (GCS) recently implicated in constructing the characteristic azadithiolate bridge of the H-cluster. According to the calculations, the lipoate cofactor could transiently coordinate the HydF cluster, helping position reactive intermediates near the diiron precursor. The results resolve a major controversy in hydrogenase research and provide new insight into how iron-sulfur clusters can guide the assembly of complex organometallic cofactors. More broadly, understanding how biological systems build delicate metal catalysts with atomic precision may inspire new strategies for designing artificial catalysts for sustainable hydrogen production and utilization. This story is part of Science X Dialog, where researchers can report findings from their published research articles. Visit this page for information about Science X Dialog and how to participate. Publication details Giorgio Caserta et al, A Non‐Covalent [4Fe–4S]/[2Fe] Interface in HydF Guides [FeFe]‐Hydrogenase Maturation, Angewandte Chemie International Edition (2026). DOI: 10.1002/anie.8078898 Journal information: Angewandte Chemie International Edition Provided by Technical University of Berlin Giorgio Caserta is a postdoctoral researcher at the Technical University of Berlin, investigating metalloenzymes involved in energy conversion, particularly hydrogenases. Caserta's work combines protein chemistry, enzymology, and biophysics with advanced spectroscopy—including infrared, and synchrotron-based methods such as NRVS—to capture and characterize how enzymes manage complex chemical transformations. Caserta is passionate about applying analytical rigor and interdisciplinary knowledge to understand complex biological systems and support scientific innovation.