Highly soluble and stable recombinant holo-phycocyanin alpha subunit expressed in Escherichia coli

C-phycocyanin (Cpc) is one of the phycobiliproteins with highly fluorescent and various pharmacological activities. Holo-Cpc-α subunit (holo-CpcA) expressed in Escherichia coli resulted in low yield and tended to aggregate after purification. In this study, we constructed a new plasmid coding holo-CpcA fused with hexahistidine and maltose-binding protein tag, which designated as HMCpcA, to improve its solubility and stability without the impairment of its spectra and fluorescent properties. HMCpcA was significantly more stable over time and a wider range of pH as compared to holo-CpcA. In addition, both the solubility and yields of HMCpcA increase significantly. We here provided an example to demonstrate that MBP could also improve the stability of the protein it fused while it has been reported as a soluble fusion partner before. This novel fluorescent protein will facilitate the large-scale production and be potentially applicable for the development of fluorescent probes, as well as antioxidant agents.