RESUMO
The Pichia anomala gene PPHY, which codes for a cell-bound phytase, was isolated from genomic DNA by PCR, using oligonucleotide sequences derived from the N-terminal region of the purified phytase protein (Pphyp) and a degenerate primer derived from conserved sequences of yeast and fungal phytases as primers. The gene harbours an ORF of 1389bp, encoding a 462-amino-acid protein. The deduced amino acid sequence has similarity, to a varied extent, with those of phosphatases from Pichia stipitis (62%), Candida dubliniensis (51%), Candida albicans (51%), Arxula adeninivorans (35%) and phytases from Debaryomyces castellii (50%) and Pichia fabianii (39%). The sequence contains the phytase consensus heptapeptide motif (-Arg-His-Gly-X-Arg-X-Pro-) as well as two phosphohistidine signature motifs found in histidine acid phosphatases. After transformation of PPHY into the yeasts Saccharomyces cerevisiae, A. adeninivorans and Hansenula polymorpha, the last species was selected as the most suitable for synthesis of recombinant Pphyp. The cell-bound enzyme activities produced by wild-type P. anomala and transgenic H. polymorpha strains bearing the PPHY gene placed under the control of the inducible H. polymorpha-derived FMD promoter were characterized. In both cases, a molecular mass of approximately 380kDa was determined for the native enzyme (corresponding to a hexamer); the pH and temperature optima for the activity were 4.0 and 60 degrees C, respectively. The enzyme was active on phytic acid, p-nitrophenylphosphate, glucose-6-phosphate, ADP, sodium pyrophosphate, AMP, 1-naphthylphosphate and ATP. Based on the K(m)/K(cat) and further biochemical parameters, the enzyme was classified as a cell-bound phytase with acid phosphatase activity and not as acid phosphatase, despite its strong similarity to the latter class of enzymes. The yeast biomass containing phytase has been demonstrated to be useful as a feed additive in poultry and aquaculture, and dephytinization of foods and feeds.
