Identification, purification, biochemical and mass spectrometric characterization of novel phycobiliproteins from a marine red alga, Centroceras clavulatum

Phycobilisomes are light-harvesting protein complexes and are widely distributed in red algae and cyanobacteria. Each phycobilisome contains highly fluorescent protein components called phycobiliproteins. Based upon the distinct physiochemical properties, phycobiliproteins are classified as allophycocyanin, phycocyanin, phycoerythrin and phycoerythrocyanin. In the present study, we describe purification and structural characterization of a novel phycocyanin and phycoerythrin isolated from a marine red macroalga, Centroceras clavulatum. The absorbance and fluorescence studies indicated that the purified proteins belong to R-Phycocyanin (R-PC) and R-Phycoerythrin (R-PE). The single bands under native-polyacrylamide gel electrophoresis revealed the intact molecular weights of R-PC and R-PE as 110kDa and 250kDa. The polypeptide compositions of the two proteins were demonstrated by SDS-PAGE. The result showed that R-PC contains two bands at 17 and 21kDa and were identified as α and β subunits through mass spectrometry based proteomics experiments. SDS-PAGE of R-PE showed three distinct bands at 18, 19 and 35kDa and was subsequently identified as α, β and γ subunits. The near-complete amino acid sequences of α and β subunits of R-PC and R-PE were derived from mass spectrometric data combined with Mascot software and multiple de novo sequencing tools followed by homology search and manual validation.