Structural dissection of Shewanella oneidensis old yellow enzyme 4 bound to a Meisenheimer complex and (nitro)phenolic ligands.

Shewanella oneidensis, a Gram-negative γ-proteobacterium with an extensive redox capacity, possesses four old yellow enzyme (OYE) homologs. Of these, Shewanella yellow enzyme 4 (SYE4) is implicated in resistance to oxidative stress. Here, we present a series of high-resolution crystal structures for SYE4 in the oxidized and reduced states, and in complex with phenolic ligands and the nitro-aromatic explosive picric acid. The structures unmask new features, including the identification of a binding platform for long-chain hydrophobic molecules. Furthermore, we present the first structural observation of a hydride-Meisenheimer complex of picric acid with a flavoenzyme. Overall, our study exposes the binding promiscuity of SYE4 toward a variety of electrophilic substrates and is consistent with a general detoxification function for SYE4.