Characterization of the T7 promoter system for expressing penicillin acylase in Escherichia coli

The pac gene encoding penicillin acylase (PAC) was overexpressed under the regulation of the T7 promoter in Escherichia coli. PAC, with its complex formation mechanism, serves as a unique target protein for demonstration of several key strategies for enhancing recombinant protein production. The current T7 system for pac overexpression was fraught with various technical hurdles. Upon the induction with a conventional inducer of isopropyl-beta-D-thiogalactopyranoside (IPTG), the production of PAC was limited by the accumulation of PAC precursors (proPAC) as inclusion bodies and various negative cellular responses such as growth inhibition and cell lysis. The expression performance could be improved by the coexpression of degP encoding a periplasmic protein with protease and chaperone activities. In addition to IPTG, arabinose was shown to be another effective inducer. Interestingly, arabinose not only induced the current T7 promoter system for pac expression but also facilitated the posttranslational processing of proPAC for maturation, resulting in significant enhancement for the production of PAC. Glycerol appeared to have an effect similar to, but not as significant as, arabinose for enhancing the production of PAC. The study highlights the importance of developing suitable genetically engineered strains with culture conditions for enhancing recombinant protein production in E. coli.