The discovery of a novel R-phycoerythrin from an antarctic red alga

A novel biliprotein, named R-phycoerythrin IV, has been discovered. It absorbs blue light better than any other known red algal biliprotein. The protein was found in Phyllophora antarctica, a benthic macroalga, which grows beneath the coastal waters of McMurdo Sound, Antarctica. Fluorescence emission and fluorescence excitation polarization spectroscopy demonstrated that R-phycoerythrin IV behaved as a typical R-phycoerythrin in the functioning of energy migration and has an emission maximum at 577 nm. The circular dichroism (CD) spectrum of the chromophores was compared with visible absorption spectrum, and both were deconvoluted. This process showed the energy states of various individual chromophores. The molecular weight of the protein suggested a alpha6beta6gamma polypeptide structure, and far UV CD studies revealed polypeptides with highly alpha-helical secondary structures. Dynamic light scattering indicated that the protein had a 5.54 nm radius, and its shape was nonspherical. R-phycoerythrin was also purified from a second benthic Antarctic red alga, Iridaea cordata. Its spectroscopic properties were similar to those of some R-phycoerythrins from nonpolar regions. The unique spectroscopic properties of R-phycocerythrin IV may help enable the alga to occupy its niche deeper in the water column than the red alga that has the typical R-phycoerythrin.