title: Engineering of phytase for improved activity at low pH.
abstract: For industrial applications in animal feed, a phytase of interest must be optimally active in the pH range prevalent in the digestive tract. Therefore, the present investigation describes approaches to rationally engineer the pH activity profiles of Aspergillus fumigatus and consensus phytases. Decreasing the negative surface charge of the A. fumigatus Q27L phytase mutant by glycinamidylation of the surface carboxy groups (of Asp and Glu residues) lowered the pH optimum by ca. 0.5 unit but also resulted in 70 to 75% inactivation of the enzyme. Alternatively, detailed inspection of amino acid sequence alignments and of experimentally determined or homology modeled three-dimensional structures led to the identification of active-site amino acids that were considered to correlate with the activity maxima at low pH of A. niger NRRL 3135 phytase, A. niger pH 2.5 acid phosphatase, and Peniophora lycii phytase. Site-directed mutagenesis confirmed that, in A. fumigatus wild-type phytase, replacement of Gly-277 and Tyr-282 with the corresponding residues of A. niger phytase (Lys and His, respectively) gives rise to a second pH optimum at 2.8 to 3.4. In addition, the K68A single mutation (in both A. fumigatus and consensus phytase backbones), as well as the S140Y D141G double mutation (in A. fumigatus phytase backbones), decreased the pH optima with phytic acid as substrate by 0.5 to 1.0 unit, with either no change or even a slight increase in maximum specific activity. These findings significantly extend our tools for rationally designing an optimal phytase for a given purpose.
authors.affiliation: Biotechnology Department, Roche Vitamins, Ltd., 4070 Basel, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Tomschy
authors.forename: Roland
authors.initials: R
authors.lastname: Brugger
authors.forename: Martin
authors.initials: M
authors.lastname: Lehmann
authors.forename: Allan
authors.initials: A
authors.lastname: Svendsen
authors.forename: Kurt
authors.initials: K
authors.lastname: Vogel
authors.forename: Dirk
authors.initials: D
authors.lastname: Kostrewa
authors.forename: Søren F
authors.initials: SF
authors.lastname: Lassen
authors.forename: Dominique
authors.initials: D
authors.lastname: Burger
authors.forename: Alexandra
authors.initials: A
authors.lastname: Kronenberger
authors.forename: Adolphus P G M
authors.initials: AP
authors.lastname: van Loon
authors.forename: Luis
authors.initials: L
authors.lastname: Pasamontes
authors.forename: Markus
authors.initials: M
authors.lastname: Wyss
mesh_terms: D010832:6-Phytase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001232:Aspergillus fumigatus / Q000201:enzymology* / Q000235:genetics; D005818:Genetic Engineering / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016415:Sequence Alignment
chemical_list: D010832:6-Phytase