What evidences were elucidated about photoreactive nitrile hydratase?

Characteristic features of a photoreactive nitrile hydratase (NHase) from Rhodococcus sp. N-771 were introduced. We have found a new biological function of nitric oxide (NO) that controls the photoreactivity of NHase by association with the non-heme iron active center and photoinduced dissociation from it. We have elucidated the crystal structure of NHase in the nitrosylated state at 1.7 Å resolution. A unique structure of the photoreactive catalytic center of the enzyme was revealed; the center consists of the non-heme iron atom coordinated with the sulfur atoms from three cysteine residues (αCys109, αCys112 and αCys114) and two amide nitrogen atoms in the main chain of αSer113 and αCys114. Two out of the three cysteine residues are post-translationally modified into cysteine sulfinic (αCys112-SO2H) and -sulfenic (αCys114-SOH) acids. The two oxygen atoms of αCys112-SO2H and αCys114-SOH form a unique structure, Claw setting, together with the oxygen atom, form αSer113. We have also studied the roles of the hydration water molecules in the enzyme. The hydration water molecules stabilize the catalytic center and the tertiary and quaternary structures of the enzyme. The detailed hydration structure around the active center is also discussed.