Connecting color with assembly in the fluorescent B-phycoerythrin protein complex

Phycoerythrin is the major light-harvesting pigment protein in red algae and is nowadays widely used as a fluorescent probe in biotechnological applications such as flow cytometry and immunofluorescence microscopy. In addition, it has had substantial economic impact due to its potential as a natural food colorant. However, knowledge on the precise molecular composition of phycoerythrin is limited. Here, we use a combination of high-resolution native mass spectrometry (MS) and fluorescence spectroscopy to characterize the assembly properties of the B-phycoerythrin protein complex from Porphyridium cruentum. Our data highlight the stabilizing role of the γ subunit in the intact B-phycoerythrin protein complex. In addition, by native MS we monitor B-phycoerythrin (dis)assembly intermediates, providing insight into which species contribute to B-phycoerythrins color and the factors that give B-phycoerythrin its highly fluorescent properties. Together, the data provide significant insights into the structural properties of B-phycoerythrin which is beneficial for its use within the biotechnology industry.