Overproduction of a thermostable 4-alpha-glucanotransferase by codon optimization at N-terminus region

Abstract

Background4--Glucanotransferases are useful enzymes to modify starch owing to their transglycosylation activity. In this study, codon optimizations were conducted to overproduce a thermostable4--glucanotransferase from Thermus thermophilus (TTGT). ResultsTwo variants, termed TTGT-P4CCG and TTGT-mut6, were constructed, which have the optimized codon at the first rare codon and optimized codons at all six chosen rare codons at the N-terminus of TTGT, respectively. In the Escherichia coli system, the expression of both optimized genes was enhanced by about 100-fold relative to that of the original gene, whereas all six mutated codons contributed to the overall enhancement of TTGT production in Bacillus subtilis. On the basis of the GTase activity of the crude cell extracts, relative activities of 1:2.9:5.8 were determined for TTGT, TTGT-P4CCG and TTGT-mut6, respectively, in B. subtilis. In addition, the activity of TTGT-mut6 from B. subtilis grown without antibiotics was as much as that with the antibiotics. Finally, after heat treatment, the specific activity of TTGT-mut6 from B. subtilis was 1.5-fold greater than that from E. coli. ConclusionThe codon-optimized TTGT that was produced in a GRAS microorganism, B. subtilis, without the selection antibiotics is potentially useful in the food industry as a food-grade enzyme. (c) 2013 Society of Chemical Industry