ABSTRACT
The inulin fructotransferase (DFA III-forming)(EC 4.2.2.18) gene in Nonomuraea sp. ID06-A0189 was amplified from genomic DNA, sequenced and expressed in Escherichia coli. The 1326-bp gene, designated as Nsp-ift, encodes a protein composed of a putative 37-amino-acid signal peptide and 404-amino-acid mature protein. A putative ribosomal binding sequence was identified 12 bases upstream from the start codon. However, a typical bacterial promoter could not be found by in silico analysis. The deduced amino-acid sequence of the enzyme was most similar to that of inulin fructotransferase (DFA I-forming) in Frankia sp. EAN1pec. Phylogenetic analysis of deduced amino-acid sequences indicated that Nonomuraea sp. ID06-A0189 and Frankia sp. EAN1pec inulin fructotransferases formed a distinct clade from those from Arthrobacter sp. H65-7, A. globiformis and Bacillus sp. snu-7 that showed 57, 56 and 56% identity to that of Nsp-ift, respectively. The Nsp-ift without a putative signal peptide was successfully expressed in E. coli and partially purified using His-tag affinity chromatography. The recombinant enzyme displayed optimum temperature between 65 and 70 °C, optimum pH between 5.5 and 6.0 and remained stable up to 70 °C. The properties were identical to those of the original enzyme. Of 10 Nonomuraea species tested by Southern hybridization, enzyme activity measurements and PCR, only Nonomuraea sp. ID06-A0189 has the Nsp-ift gene, suggesting that Nsp-ift is not highly conserved in this genus.
Subject(s)
Actinomycetales/enzymology , Bacterial Proteins/classification , Bacterial Proteins/metabolism , Hexosyltransferases/chemistry , Hexosyltransferases/classification , Actinomycetales/genetics , Amino Acid Sequence , Bacterial Proteins/genetics , Catalysis , Cloning, Molecular , Conserved Sequence , DNA, Bacterial/genetics , Escherichia coli/genetics , Escherichia coli/metabolism , Genes, Bacterial/genetics , Hexosyltransferases/genetics , Phylogeny , Promoter Regions, Genetic , Sequence Analysis, DNAABSTRACT
Phytase, an enzyme that catalyzes the hydrolysis of phytate, was purified from Klebsiella pneumoniae 9-3B. The isolate was preferentially selected in a medium which contains phytate as a sole carbon and phosphate source. Phytic acid was utilized for growth and consequently stimulated phytase production. Phytase production was detected throughout growth and the highest phytase production was observed at the onset of stationary phase. The purification scheme including ion exchange chromatography and gel filtration resulted in a 240 and 2077 fold purification of the enzyme with 2% and 15% recovery of the total activity for liberation of inorganic phosphate and inositol, respectively. The purified phytase was a monomeric protein with an estimated molecular weight of 45kDa based on size exclusion chromatography and SDS-PAGE analyses. The phytase has an optimum pH of 4.0 and optimum temperature of 50°C. The phytase activity was slightly stimulated by Ca(2+) and EDTA and inhibited by Zn(2+) and Fe(2+). The phytase exhibited broad substrate specificity and the K(m) value for phytate was 0.04mM. The enzyme completely hydrolyzed myo-inositol hexakisphosphate (phytate) to myo-inositol and inorganic phosphate. The properties of the enzyme prove that it is a good candidate for the hydrolysis of phytate for industrial applications.
