Radical-based chemistry for the assembly of the [FeFe]-hydrogenase active site

[FeFe] hydrogenases are metalloenzymes capable of catalyzing the reversible oxidation of molecular hydrogen. They use a unique organometallic center called H-aggregate, consisting of a [Fe4S4] center linked to a binuclear iron center [2Fe]H. The latter corresponds to the hydrogen binding and conversion site. The physicochemical and structural properties of this center serve as a source of inspiration for the development of catalysts for the wider use of molecular hydrogen as a renewable energy source. IRIG researchers are unveiling the mechanisms of production and assembly of this metal center, which involve a complex radical chemistry .

The biosynthesis of [2Fe]H requires the coordinated action of at least three accessory metalloproteins HydF, HydE and HydG. HydG is responsible, from L-tyrosine, for the production of the ligands cyanide and carbon monoxide, in the form of an organometallic complex termed complex-B. The latter serves in turn as a substrate for HydE whose reaction and product remain unknown. HydF serves as a scaffold on which the [2Fe]H center is built before being inserted into the hydrogenase. Researchers from Irig are studying the catalytic mechanisms of transition metal containing metalloenzymes, but also the mechanisms of synthesis and insertion of these metal sites into the enzymes in which they are to be inserted. In collaboration with UCDavis and the University of Illinois, they published the complex-B bound HydE crystal structure, revealing for the first time both its unique (3-cysteinate)Fe(CN)(CO)2 configuration and its binding mode. Furthermore, by triggering the reaction, either directly in the crystals or just before crystallization, they were able to observe a new mononuclear pentavalent iron species, probably related to the product of HydE. Analysis of the conformational changes observed in the different structures suggests a directional movement for substrate access to the active site and product evacuation, allowing them to be protected from possible hydrolysis upon contact with the solvent. This work raises new questions about the complete mechanism of the enzyme which acts as a nano assembly line.

Crystal Structure of the [FeFe]-Hydrogenase Maturase HydE Bound to Complex-B. Rohac R, Martin L, Liu L, Basu D, Tao L, Britt RD, Rauchfuss TB, and Nicolet Y. Journal of the American Chemical Society, 2021

Contact : Yvain Nicolet (IBS/Metalloproteins Group)