Efficient Biosynthesis of Phycocyanin Holo-β Subunits in Escherichia coli and Their Stability and Antioxidant Properties

Phycocyanin is a biliprotein that has been used as a natural food colorant due to its brilliant color. However, their application is limited by their poor stability. In this study, biosynthesis pathways of two phycocyanin holo-β subunits, CpcB^A from mesophilic Arthrospira platensis and CpcB^T from thermophilic Thermosynechococcus elongatus BP-1, were constructed in Escherichia coli. Coexpression of ferredoxin (Fd), Fd-NADP⁺ reductase (FNR), and NADP-specific glutamate dehydrogenase (gdhA) enabled full chromophorylation of these recombinant CpcBs in recombinant E. coli. These fully chromophorylated CpcBs were visually redder and had higher hydroxyl radical and peroxyl radical scavenging activities than the partially chromophorylated CpcBs. Comparative study on thermostability showed that at high temperature the CpcB^T had lower denature rate constants and longer half-life values than the CpcB^A. Both proteins were stable at acidic pH (3.0-6.6), except for the CpcB^A at pH 3.0. Under a combinational treatment of acid pH and heat, CpcB^A showed remarkable losses (93.6-98.4%) while CpcB^T showed much less losses (20.0-49.6%). All the results indicated that CpcB^T was a stable phycocyanin and could potentially be developed as an excellent colorant in the food industry.