Cloning and expression of Allophycocyanin gene from Gracilariopsis lemaneiformis and studying the binding sites of phycocyanobilin on its α and β subunits

Allophycocyanin (APC) is a pigment-protein with optical activity in the core of phycobilisomes of cyanobacteria and red algae. Its wide application prospects make it necessary to carry out the recombinant expression of allophycocyanin with optical activity. In this study, apcA and apcB genes encoding two subunits of allophycocyanin were cloned from Gracilariopsis lemaneiformis. Then apcA and apcB genes expressed in Escherichia coli to obtain allophycocyanin. In order to investigate the active sites of allophycocyanin to bind with phycocyanobilin, the Cys-81 and Cys-138 of α subunit and Cys-81 and Cys-157 of β subunit were mutated. SDS-PAGE and Western blotting results verified the expression of allophycocyanin. The fluorescence emission spectra showed the characteristic fluorescence peak of allophycocyanin, which indicated that the recombinant allophycocyanin had optical activity. The recombinant strains with chromophore lyases—CpcU and CpcS—had the higher fluorescence emission peak, indicating that chromophore lyases would catalyze the combination of phycocyanobilin and apo-allophycocyanin more effectively. The binding sites were Cys-81 and Cys138 of allophycocyanin α subunit, and Cys-81 and Cys-157 of allophycocyanin β subunit. The catalytic effect of CpeT was not obvious. This research provides an experimental foundation for understanding the synthesis mechanism of optically active allophycocyanin in G. lemaneiformis.