ABSTRACT
Aspergillus fumigatus wild-type phytase has many favorable properties, such as a good thermorstability and a broad pH optimum. However, the specific activity of the enzyme is relative low. A. fumigatus Q23L phytase resulted in a remarkable increase in specific activity around pH4.5 - 7.0, but the pH stability of Q23L was lower than A. fumigatus wild-type phytase. To increase the pH stability of Q23L, the mutant Q23LG272E was constructed by site-directed mutagenesis with PCR. The gene of A. fumigatus wild-type phytase and the mutant genes encoding the Q23LG272E and the Q23L were correctly expressed in Pichia pastoris GS115. Enzymes were purified and their enzymatic properties were determined. The results revealed that the specific activity of the Q23L improved remarkably, which increased from 51 u/mg of the wild type to 109 u/mg at pH5.5. Meanwhile, the pH stability of Q23L, decreased evidently, especially from pH3.0 to pH4.0.The pH stability of Q23LG272E in pH3.0 - 4.5 and pH6.5 - 7.0 has been improved compared with Q23L. The specific activity of Q23LG272E basically maintained at the level of Q23L. Analysis of 3-D structure and sequence similarity were used to reveal the presumable factors influencing the enzymatic properties of Q23LG272E, and discussion for the relationship between structure and function of phytase was given.
Subject(s)
6-Phytase , Chemistry , Genetics , Metabolism , Amino Acid Substitution , Aspergillus fumigatus , Genetics , Biocatalysis , Electrophoresis, Polyacrylamide Gel , Fungal Proteins , Chemistry , Genetics , Metabolism , Hydrogen-Ion Concentration , Models, Molecular , Mutagenesis, Site-Directed , Mutant Proteins , Genetics , Metabolism , Mutation , Pichia , Genetics , Polymerase Chain Reaction , Protein Conformation , Protein Engineering , Methods , Recombinant Proteins , Metabolism , Structure-Activity Relationship , Substrate SpecificityABSTRACT
A gene appA encoding a novel phytase was firstly cloned from Hafnia alvei by PCR and sequenced. The gene was consisted of 1335 bp, encoding 444 amino acids. The calculated molecular weight of the mature APPA was about 45.2 kD. The gene appA was expressed in E. coli BL21 (DE3). Recombinant APPA was purified and its enzymatic properties were determined. The optimum pH for the enzyme was 4.5 and the optimum temperature was 60 degrees C. The pH stability of r-APPA is good, the relative phytase activity was above 80% after treated in buffers of pH 2.0-10.0. The specific activity of r-APPA is 356.7 U/mg, and the Km value was 0.49 mmol/L and Vmax of 238 U/mg. The enzyme showed resistance to pepsin and trypsin treatment.
Subject(s)
6-Phytase , Genetics , Amino Acid Sequence , Cloning, Molecular , Escherichia coli , Genetics , Metabolism , Hafnia , Genetics , Hydrogen-Ion Concentration , Molecular Sequence Data , Recombinant Proteins , Genetics , Metabolism , TemperatureABSTRACT
In order to improve the fermentation potency of phytase in recombinant host and decrease the production cost, the pichia expression vector pGAPZalpha-A was modified by introduction of an AOX1 promoter from vector pPIC9 and the resulted vector pAOXZalpha is an methanol induced vector. After that, a phytase gene appA-m was cloned into pAOXZalpha to construct the recombinant vector pAOXZalpha-appA-m. The recombinant Pichia pastoris 74#, which already contains one copy of appA-m and its fermentation potency exceeded 7.5 x 10(6) IU/mL, was used as the host strain for the transformation of pAOXZalpha-appA-m. The Pichia pastoris transformants were gained by electroporation. PCR results indicated that the appA-m expression box has integrated into the genome of Pichia pastoris and the original construction of phytase gene has not changed. SDS-PAGE analysis revealed that phytase was overexpressed and secreted into the medium supernatant. Recombinants with high expression level were screened and used for fermentation. In 5L fermentor, the expression level of phytase protein achieved 4 mg/mL and the phytase activity (fermentation potency) exceeded 1.2 x 10(7) IU/mL, which was about 1.6-fold compared with that of the host strain 74#. Moreover, the improved recombinant Pichia pastoris is excellent at expression stability and heredity stability.
Subject(s)
6-Phytase , Genetics , Fermentation , Gene Dosage , Pichia , Genetics , Plasmids , Polymerase Chain Reaction , Recombination, GeneticABSTRACT
By functional plates,16 strains which can produce?-mannana-se were isolated frnm 28 Bacillus spp.Using a pair of degenerated primers,the conserved fragments of?-mannanase gene from the selected strains were amplified by PCR.The obtained nucleotide fragments were sequenced and compared with the homologous?-mannanase genes in GenBank and a phylogenetic tree was generated.Comparing to the genes coding?-mannanase published,the cloned nucleotide fragments show the highest sequence identity between 62% and 98%.The genes coding fnr?-mannanase of Bacillus circulus have low identity while the?-mannanase genes of Bacillus subtilis and other Bacillus spp. have high identity.