High-level excretion of heterologous proteins from E-coli directed by protein A singal peptide

Several plasmids were constructed by inserting the staphylococcal protein A signal-encoding sequence at the 5'-terminal of recombinant genes or DNA fragments controlled under various promoters, and the study of secretion expression was carried out. High level products which were secreted to the periplasmic space were observed in E.coli harboring plasmids controlled by PL promoter. By optimizing the expression conditions such as the E. coli host, medium, temperature, and pH, some recombinant proteins could be secreted to the culture medium at a level of 100 mg/L (with the concentration of bacteria at 1 A(000)/ml). With this excretion system, four recombinant proteins, protein A, its EDA (PB-EDA)and ABC: (PA-ABO) domains, and its fusion protein with insulin-like growth factor I (PA-IGF-I), were highly expressed and successfully excreted from E. coli to the medium. The N-terminal analysis of these proteins showed that the signal peptides were processed correctly.