Extracellular mannose-6-phosphatase of Phanerochaete chrysosporium: A lignin peroxidase-modifying enzyme

The Lignin peroxidase (LIP) isozyme profile of the white-rot fungus Phanero chaete chrysosporium changes markedly with culture age. This change occurs extracellularly and results from enzymatic dephosphorylation of LIP isozyme s. In this study, a novel mannose 6-phosphatase (M6Pase) from extracellular culture fluid filtrate of P. chrysosporium, shown to be responsible for th e extracellular postranslational modification of LIP, was purified and char acterized. In vitro incubation of the purified M6Pase with purified LIP iso zyme H2 resulted in its conversion to isozyme H1, with an equimolar release of orthophosphate. Using different sugar phosphates as substrate, the enzy me exhibited narrow specificity, showing activity mostly for mannose 6-phos phate (K-m = 0.483 mM). The enzyme displayed a molecular mass of 82 kDa, as determined by gel filtration, and 40.4 and 39.1 kDa, on SDS-PAGE, suggesti ng that the native form is a dimer. The N-terminal sequence of the enzyme h as no homology with that of other reported phosphatases. M6Pase is a metalo protein with manganese and cobalt as the preferred metal ions. It is N-glyc osylated proteins with an isoelectric point of 4.7-4.8 and a pH optimum of 5. Based on its characteristics, M6Pase from P. chrysosporium seems to be a unique phosphatase responsible for posttranslation modification of LTP iso zymes. (C) 1999 Academic Press.