摘要
Molecular mechanisms underlying the repair of nitrosylated [Fe–S] clusters by the microbial protein YtfE remain poorly understood. The X-ray crystal structure of YtfE, in combination with EPR, magnetic circular dichroism (MCD), UV, and 17 O-labeling electron spin echo envelope modulation measurements, show that each iron of the oxo-bridged Fe II –Fe III diiron core is coordinatively unsaturated with each iron bound to two bridging carboxylates and two terminal histidines in addition to an oxo-bridge. Structural analysis reveals that there are two solvent-accessible tunnels, both of which converge to the diiron center and are critical for capturing substrates. The reactivity of the reduced-form Fe II –Fe II YtfE toward nitric oxide demonstrates that the prerequisite for N 2 O production requires the two iron sites to be nitrosylated simultaneously. Specifically, the nitrosylation of the two iron sites prior to their reductive coupling to produce N 2 O is cooperative. This result suggests that, in addition to any repair of iron centers (RIC) activity, YtfE acts as an NO-trapping scavenger to promote the NO to N 2 O transformation under low NO flux, which precedes nitrosative stress.