Development of an efficient recombinant expression system of alanine aminotransferase

Abstract

Objective To develop an efficient recombinant expression system of alanine aminotransferase (ALT) in order to build the foundation for the preparation of feedstock related ALT reference materials. Methods A new human ALT gene was synthesized by optimizing the codons of the nucleic acid sequence encoding human ALT using bioinformatic tools, and then it was cloned into pRSF-Duet expression vector. The recombinant plasmid pRSF-Duet-ALT was transformed into E. coli BL21 and the target protein expression was induced by 2 mmol/L isopropyl β-D-1-thiogalactopyranoside (IPTG). The expression condition for soluble protein was optimized by changing the inducer concentration, shaking speed and induction temperature. The soluble protein was purified by nickel ion affinity chromatography and dextran molecular sieve chromatography, and identified by sodium dodecyl sulfate-polyacrylamide gelelectrophoresis（SDS-PAGE）and Western blot analysis. The activity and stability of recombinant proteins in serum matrix under different storage conditions were detected. Results The usage frequency in E. coli of ALT codons was more than 10% after codon optimization. The expressions of soluble proteins were increased by optimizing the induced expression conditions, including a final concentration of 2 mmol/L of IPTG, and continued incubation with shaking at 150 rpm for 8 h at 25 ℃. The purified protein was identified as ALT by SDS-PAGE and Western blot with ALT activities of up to 80 000 U/L. Recombinant ALT could be stable for 2-8 d at 2-8 ℃ or 25 ℃ with a relative standard deviation of less than 5%. Conclusions An efficient recombinant expression system of ALT was developed successfully by codons optimization. The obtained recombinant protein could achieve the requirements of reference material feedstock.（Chin J Lab Med，2014,37：767-771） Key words: Alanine transaminase; Recombinant proteins; Codon; Reference standards