Crystal Structure of the [FeFe]-Hydrogenase Maturase HydE Bound to Complex‑B

• Published in: Journal of the American Chemical Society 2021-06, Vol.143 (22), p.8499-8508
• Main Authors: Rohac, Roman, Martin, Lydie, Liu, Liang, Basu, Debashis, Tao, Lizhi, Britt, R. David, Rauchfuss, Thomas B, Nicolet, Yvain
• Format: Article
• Language: English
• Subjects: Biochemistry, Molecular Biology; Hydrogenase - chemistry; Hydrogenase - metabolism; Iron-Sulfur Proteins - chemistry; Iron-Sulfur Proteins - metabolism; Life Sciences; Models, Molecular; Protein Conformation; Structural Biology
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.1c03367

[FeFe]-hydrogenases use a unique organometallic complex, termed the H cluster, to reversibly convert H2 into protons and low-potential electrons. It can be best described as a [Fe4S4] cluster coupled to a unique [2Fe]H center where the reaction actually takes place. The latter corresponds to two iron atoms, each of which is bound by one CN– ligand and one CO ligand. The two iron atoms are connected by a unique azadithiolate molecule (−S–CH2–NH–CH2–S–) and an additional bridging CO. This [2Fe]H center is built stepwise thanks to the well-orchestrated action of maturating enzymes that belong to the Hyd machinery. Among them, HydG converts l-tyrosine into CO and CN– to produce a unique l-cysteine-Fe­(CO)2CN species termed complex-B. Very recently, HydE was shown to perform radical-based chemistry using synthetic complex-B as a substrate. Here we report the high-resolution crystal structure that establishes the identity of the complex-B-bound HydE. By triggering the reaction prior to crystallization, we trapped a new five-coordinate Fe species, supporting the proposal that HydE performs complex modifications of complex-B to produce a monomeric “SFe­(CO)2CN” precursor to the [2Fe]H center. Substrate access, product release, and intermediate transfer are also discussed.