title: High level expression of a recombinant acid phytase gene in Pichia pastoris.
abstract: OBJECTIVE
  To achieve high phytase yield with improved enzymatic activity in Pichia pastoris.
  
  
  RESULTS
  The 1347-bp phytase gene of Aspergillus niger SK-57 was synthesized using a successive polymerase chain reaction and was altered by deleting intronic sequences, optimizing codon usage and replacing its original signal sequence with a synthetic signal peptide (designated MF4I) that is a codon-modified Saccharomyces cerevisiae mating factor alpha-prepro-leader sequence. The gene constructs containing wild type or modified phytase gene coding sequences under the control of the highly-inducible alcohol oxidase gene promoter with the MF4I- or wild type alpha-signal sequence were used to transform Pichia pastoris. The P. pastoris strain that expressed the modified phytase gene (phyA-sh) with MF4I sequence produced 6.1 g purified phytase per litre of culture fluid, with the phytase activity of 865 U ml(-1). The expressed phytase varied in size (64, 67, 87, 110 and 120 kDa), but could be deglycosylated to produce a homogeneous 64 kDa protein. The recombinant phytase had two pH optima (pH 2.5 and pH 5.5) and an optimum temperature of 60 degrees C.
  
  
  CONCLUSIONS
  The P. pastoris strain with the genetically engineered phytase gene produced 6.1 g l(-1) of phytase or 865 U ml(-1) phytase activity, a 14.5-fold increase compared with the P. pastoris strain with the wild type phytase gene.
  
  
  CONCLUSIONS
  The P. pastoris strain expressing the modified phytase gene with the MF4I signal peptide showed great potential as a commercial phytase production system.
authors.affiliation: Agro-Biotechnology Research Center of Shanghai Academy of Agricultural Sciences, Shanghai, China.
authors.forename: A-S
authors.initials: AS
authors.lastname: Xiong
authors.forename: Q-H
authors.initials: QH
authors.lastname: Yao
authors.forename: R-H
authors.initials: RH
authors.lastname: Peng
authors.forename: P-L
authors.initials: PL
authors.lastname: Han
authors.forename: Z-M
authors.initials: ZM
authors.lastname: Cheng
authors.forename: Y
authors.initials: Y
authors.lastname: Li
mesh_terms: D010832:6-Phytase / Q000235:genetics*; D001483:Base Sequence; D017931:DNA Primers; D005285:Fermentation; D005516:Food Microbiology; D015870:Gene Expression; D008969:Molecular Sequence Data; D010843:Pichia / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000235:genetics; D017385:Sequence Homology; D014170:Transformation, Genetic
chemical_list: D017931:DNA Primers; D011994:Recombinant Proteins; D010832:6-Phytase