Enhanced Phycocyanobilin Production in Escherichia coli by Fusion-Expression of Apo-Proteins with Signal Peptides

Abstract

Phycocyanobilin (PCB) is the bioactive chromophore attached to Phycocyanin (PC) that is of special interest for nutraceutical and therapeutic applications. However, the production of PCB from the heterologous host Escherichia coli is still very low. To facilitate subsequent application of PCB, improving its production in microbial hosts is still a challenge to be solved. In this paper, a strategy involving fusion-expression of apo-proteins with signal peptides was adopted to improve PCB production in E. coli. First, we reconstructed the PCB biosynthesis pathway in E. coli and then optimized its culture media. Subsequently, one PC α (CpcA) subunit and one PC β (CpcB) subunit, which can capture free PCB, were introduced and increased the yield of PCB. Finally, CpcA was fused with seven signal peptides to generate recombinant proteins, among which, the signal peptide N20 fused with CpcA protein drastically improved PCB production in E. coli, providing a maximum flask output of 8.47 ± 0.18 mg/L. The results of this study demonstrate that PCB distribution and transporting manners in E. coli could affect the heterologous production efficiency. By fusing apo-proteins with signal peptides, the secretion of phycocyanin was refined and the production of PCB was successfully enhanced by 3.7-fold, compared with the starting strain (1.80 ± 0.12 mg/L). This work provided an alternative method for improving the production of PCB and other phycobilins.