Substrate specificity of lignin peroxidase and a S168W variant of manganese peroxidase

Lignin peroxidase (LiP) and manganese peroxidase (MnP) are structurally sim ilar heme-containing enzymes secreted by white-rot fungi. Unlike MnP, which is only specific for Mn2+, LiP has broad substrate specificity, but it is not known if this versatility is due to multiple substrate-binding sites. W e report here that a S168W variant of RMnP from Phanerochaete chrysosporium not only retained full Mn2+ oxidase activity, but also, unlike native or r ecombinant MnP, oxidized a multitude of LiP substrates, including small mol ecule and polymeric substrates. The kinetics of oxidation of most nonpolyme ric substrates by the MnP variant and LiP were similar. The stoichiometries for veratryl alcohol oxidation by these two enzymes were identical. Some r eadily oxidizable substrates, such as guaiacol and ferrocyanide, were oxidi zed by MnP S168W and LiP both specifically and nonspecifically while recomb inant MnP oxidized these substrates only nonspecifically. The functional si milarities between this MnP variant and LiP provide evidence for the broad substrate specificity of a single oxidation site near the surface tryptopha n. (C) 2000 Academic Press.