Cloning of Dextransucrase Gene from Leuconostoc citreum HJ-P4 and Its High-Level Expression in E. coli by Low Temperature Induction

摘要

A dextransucrase (LcDS) gene from Leuconostoc citreum HJ-P4 has been amplified and cloned in E. coli. The LcDS gene consists of 4,431 nucleotides encoding 1,477 amino acid residues sharing 63-98% of amino acid sequence identities with other known dextransucrases from Leuc. mesenteroides. Interestingly, 0.1 mM of IPTG induction at 15 degrees C remarkably increased the LcDS productivity to 19,187 U/1 culture broth, which was over 330-fold higher than that induced at 37 degrees C. Optimal reaction temperature and pH of LcDS were determined as 35 degrees C and pH 5.5 in 20 mM sodium acetate buffer, respectively. Meanwhile, 0.1 mM CaCl2 increased its activity to the maximum of 686 U/mg, which was 2.1-fold higher than that in the absence of calcium ion. Similar to the native Leuconostoc dextransucrase, recombinant LcDS could successfully produce a series of isomaltooligosaccharides from sucrose and maltose, on the basis of its transglycosylation activity.