RESUMO
OBJECTIVE: To improve expression level of glycerol dehydrogenase gene gldA in Escherichia coli by means of codon optimization. METHODS: For immediately downstream region of initiation codon in gldA, we designed optimized sequence by choosing higher AT-content synonymous, in order that this region's AT-content was increased without changing the corresponding amino acids. Then we had wild gene gldA-WT site-directed mutagenesis depending on mega-primers PCR, so that physically optimized gene gldA-4 was acquired. We cloned gldA-4 into pET-32a(+) to construct expression plasmid pET-gldA4, which was transformed into Escherichia coli BL21 (DE3) for gaining engineering bacteria E. coli-4, by contrast engineering bacteria involved gldA-WT named E. coli-WT. After E. coli-4 and E. coli-WT were fermented in shake flasks,we measured enzyme activities of expression products with glycerol as substrate. RESULTS: Four gldA-4's bases in the second, fifth and sixth codon were different with gldA-WT, so AT-content of the optimized gene was up to 80.0% higher than the wild gene's 53.3%. Furthermore, enzyme activity of E. coli-4's crude extract was 191.3 U/mL more three times than E. coli-WT's 48.3 U/mL. CONCLUSION: This optimization scheme was quick and easy, but indeed increased dehydrogenase's activity. It possible becomes a universal method to improve heterogenous expression level of target genes.
