Extended Data Fig. 1: Preparation and characterization of the PBS from P. purpureum.

a, Isolation of PBSs using sucrose density gradient centrifugation. Three visible bands were observed. Band 1 is the sample of PBSs used for single-particle analysis in this study. The purification of PBS was repeated independently at least three times with similar results. b, Analysis of the protein composition of band 1 by SDS–PAGE stained with ZnSO₄ to enable the detection of bilin-containing proteins with ultraviolet light by Zn-enhanced fluorescence. The bands of L_Rγ4, 5, 7, 8 and PBPs identified by mass spectrometric analysis are indicated. For gel source data, see Supplementary Fig. 1. The purification and characterization of the protein composition was repeated independently at least three times with similar results. c, Absorption spectrum of band 1 and the PBS from G. pacifica. The peaks at 498 nm, 620 nm and 650 nm are from phycourobilins, PCBs of phycocyanins and PCBs of allophycocyanins, respectively. The peaks at 540 nm and 565 nm are from PEBs. The reduced absorption of the P. purpureum PBS compared with the G. pacifica PBS at 498 nm indicates that the phycourobilin content of P. purpureum is much lower than that of G. pacifica. d, Fluorescence emission spectra of the three bands. Emission maxima at 580 nm and 676 nm represent the disassembled phycoerythrin hexamer and the terminal emitter in the intact PBS, respectively. Band 1 has an emission peak at 676 nm, band 2 at 580 nm and band 3 has two emission peaks at 676 nm and 580 nm, indicating that band 1 contains intact PBSs, band 2 contains free PBPs and band 3 contains partially disassembled PBSs. e, Results of the mass spectrometric analysis of purified PBSs. Two batches of sample were analysed. The similar results confirmed the consistency of our purification method.