Spatial variation and structural characteristics of phycobiliproteins from the red algae Furcellaria lumbricalis and Coccotylus truncatus

Abstract Phycobiliproteins, red phycoerythrins and blue (allo)phycocyanins, are one of the most highly valued components extracted from cyanobacteria and red algae. In the given study, 95 Furcellaria lumbricalis and 92 Coccotylus truncatus samples were collected from different locations and depths from Kassari Bay, Estonia. Firstly, a strong, positive exponential correlation between the R-phycoerythrin and allophycocyanin concentrations and the collection depth (R > 0.75 and R > 0.61, respectively) was found. Secondly, a preparative scale purification was performed, and the proteins were further characterised by spectrophotometry, fluorimetry and native mass spectrometry. The obtained purity indices (A566/A280) for the R-phycoerythrins were 1.6 for F. lumbricalis and 2.6 for C. truncatus, thus making them suitable for cosmetics and food industries. Purified R-phycoerythrins from the two algal species had subtle differences in absorption and fluorescence maxima. Based on their slightly different absorption characteristics, R-phycoerythrin from F. lumbricalis would categorise as type III (RIII-PE) and R-phycoerythrin from C. truncatus, alongside with the Sigma 52412 standard, as type II (RII-PE). The native mass spectrometry analysis supported the results by showing different intact complexes with distinct γ-subunits for the R-phycoerythrin types. The R-phycoerythrin hexamers linked to various γ-subunits, which are in turn coupled to different chromophores, could explain the similarities (analytical standard and C. truncatus) and differences (F. lumbricalis) in absorption and fluorescence characteristics among the tested species.