EPR Study of Substrate Binding to Mn(II) in Hydroxynitrile Lyase from Granulicella tundricola
journal contributionposted on 22.06.2016 by Femke Vertregt, Guzman Torrelo, Sarah Trunk, Helmar Wiltsche, Wilfred R. Hagen, Ulf Hanefeld, Kerstin Steiner
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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.