title: Site-directed mutagenesis improves catalytic efficiency and thermostability of Escherichia coli pH 2.5 acid phosphatase/phytase expressed in Pichia pastoris.
abstract: Escherichia coli pH 2.5 acid phosphatase gene (appA) and three mutants were expressed in Pichia pastoris to assess the effect of strategic mutations or deletion on the enzyme (EcAP) biochemical properties. Mutants A131N/ V134N/D207N/S211N, C200N/D207N/S211N, and A131N/ V134N/C200N/D207N/S211N had four, two, and four additional potential N-glycosylation sites, respectively. Extracellular phytase and acid phosphatase activities were produced by these mutants and the intact enzyme r-AppA. The N-glycosylation level was higher in mutants A131N/V134N/D207N/S211N (48%) and A131N/V134N/ C200N/D207N/S211N (89%) than that in r-AppA (14%). Despite no enhancement of glycosylation, mutant C200N/ D207N/S211N was different from r-AppA in the following properties. First, it was more active at pH 3.5-5.5. Second, it retained more (P < 0.01) phytase activity than that of r-AppA. Third, its specific activity of phytase was 54% higher. Lastly, its apparent catalytic efficiency kcat/Km for either p-nitrophenyl phosphate (5.8 x 10(5) vs 2.0 x 10(5) min(-1) M(-1)) or sodium phytate (6.9 x 10(6) vs 1.1 x 10(6) min(-1) M(-1)) was improved by factors of 1.9- and 5.3-fold, respectively. Based on the recently published E. coli phytase crystal structure, substitution of C200N in mutant C200N/D207N/S211N seems to eliminate the disulfide bond between the G helix and the GH loop in the alpha-domain of the protein. This change may modulate the domain flexibility and thereby the catalytic efficiency and thermostability of the enzyme.
authors.affiliation: Department of Animal Science, Cornell University, Ithaca, New York 14853, USA.
authors.forename: E
authors.initials: E
authors.lastname: Rodriguez
authors.forename: Z A
authors.initials: ZA
authors.lastname: Wood
authors.forename: P A
authors.initials: PA
authors.lastname: Karplus
authors.forename: X G
authors.initials: XG
authors.lastname: Lei
mesh_terms: D010832:6-Phytase / Q000378:metabolism*; D000135:Acid Phosphatase / Q000378:metabolism*; D000595:Amino Acid Sequence; D001483:Base Sequence; D002384:Catalysis; D003001:Cloning, Molecular; D004220:Disulfides; D004591:Electrophoresis, Polyacrylamide Gel; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology*; D006031:Glycosylation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009596:Nitrophenols / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000378:metabolism; D010833:Phytic Acid / Q000378:metabolism; D010843:Pichia / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D017434:Protein Structure, Tertiary; D013696:Temperature
chemical_list: D004220:Disulfides; D009596:Nitrophenols; D009943:Organophosphorus Compounds; C008644:nitrophenylphosphate; D010833:Phytic Acid; D000135:Acid Phosphatase; D010832:6-Phytase