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EPR Study of Substrate Binding to Mn(II) in Hydroxynitrile Lyase from Granulicella tundricola

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posted on 22.06.2016, 00:00 authored by Femke Vertregt, Guzman Torrelo, Sarah Trunk, Helmar Wiltsche, Wilfred R. Hagen, Ulf Hanefeld, Kerstin Steiner
GtHNL from Granulicella tundricola is a Mn­(II) containing hydroxynitrile lyase with a cupin fold. The quasi-octahedral manganese is pentacoordinated by the enzyme. It catalyzes the enantioselective addition of HCN to aldehydes, yielding R-cyanohydrins. On the Lewis acidic vacant coordination site the Mn binds either substrate or the product, leading to a hexacoordinated 17 electron complex. EPR spectra of the active enzyme are unusually wide with a zero-field splitting approximately equal to the X-band microwave energy. A spectral change is induced by incubation with either one of the substrates/products HCN, benzaldehyde, and/or mandelonitrile. This points toward Mn­(II) catalyzed cyanohydrin synthesis.