Expression, gene cloning, and characterization of five novel phytases fromfour basidiomycete fungi: Peniophora lycii, Agrocybe pediades, a Ceriporiasp., and Trametes pubescens

Phytases catalyze the hydrolysis of phosphomonoester bonds of phytate (myo- inositol hexakisphosphate), thereby creating lower forms of myo-inositol ph osphates and inorganic phosphate. In this study, cDNA expression libraries were constructed from four basidiomycete fungi (Peniophora lycii, Agrocybe pediades, a Ceriporia sp., and Trametes pubescens) and screened for phytase activity in yeast. One full-length phytase-encoding cDNA was isolated from each library, except for the Ceriporia sp. library where two different phy tase-encoding cDNAs were found. All five phytases were expressed in Aspergi llus oryzae, purified, and characterized. The phytases revealed temperature optima between 40 and 60 degreesC and pH optima at 5.0 to 6.0, except for the P. lycii phytase, which has a pH optimum at 4.0 to 5.0. They exhibited specific activities in the range of 400 to 1,200 U . mg, of protein(-1) and were capable of hydrolyzing phytate down to myo-inositol monophosphate. Su rprisingly, H-1 nuclear magnetic resonance analysis of the hydrolysis of ph ytate by all five basidiomycete phytases showed a preference for initial at tack at the 6-phosphate group of phytic acid, a characteristic that was bel ieved so far not to be seen with fungal phytases. Accordingly, the basidiom ycete phytases described here should be grouped as 6-phytases (EC 3.1.3.26) .