Radical SAM Enzyme HydE Generates Adenosylated Fe(I) Intermediates En Route to the [FeFe]-Hydrogenase Catalytic H-Cluster
Lizhi Tao, Scott A. Pattenaude, Sumedh Joshi, Tadhg P. Begley, Thomas B. Rauchfuss, R. David Britt
Abstract
The H-cluster of [FeFe]-hydrogenase consists of a [4Fe–4S]H-subcluster linked by a cysteinyl bridge to a unique organometallic [2Fe]H-subcluster assigned as the site of interconversion between protons and molecular hydrogen. This [2Fe]H-subcluster is assembled by a set of Fe–S maturase enzymes HydG, HydE and HydF. Here we show that the HydG product [FeII(Cys)(CO)2(CN)] synthon is the substrate of the radical SAM enzyme HydE, with the generated 5′-deoxyadenosyl radical attacking the cysteine S to form a C5′–S bond concomitant with reduction of the central low-spin Fe(II) to the Fe(I) oxidation state. This leads to the cleavage of the cysteine C3–S bond, producing a mononuclear [FeI(CO)2(CN)S] species that serves as the precursor to the dinuclear Fe(I)Fe(I) center of the [2Fe]H-subcluster. This work unveils the role played by HydE in the enzymatic assembly of the H-cluster and expands the scope of radical SAM enzyme chemistry.