a, b, Structural alignment of L R γ linker proteins in the outmost hexamers of various rods from the P. purpureum PBS (a) and the G. pacifica PBS (b). β82 PEBs and residues of L R γ linker proteins are shown in ball-and-stick and stick representations, respectively. Note that an aromatic residue from the L R γ linker is present near to each β82 PEB to form π–π interactions, and one bilin from the L R γ linker \(({{\rm{\gamma }}}_{{{\rm{L}}}_{{\rm{R}}}{\rm{\gamma }}})\) always provides additional π electrons to the conjugation system of the \({{\rm{\beta }}}_{2}^{82}\) PEB. These aromatic residues and the bilins from L R γ linker proteins are conserved in both P. purpureum and G. pacifica. c, Sequence alignment of L R γ4–5 from P. purpureum and other red algae. Three aromatic residues interacting with the β82 PEBs and the cysteine residues used to link the bilins close to the β82 PEBs are marked by stars. LRgamma4_GP and LRgamma5_GP, L R γ4–5 from G. pacifica; PXF41621.1, γ-subunit from Gracilariopsis chorda; XP_005715244.1, γ-subunit from Chondrus crispus; OSX79262, γ-subunit from Porphyra umbilicalis; AAN39000.1, γ-subunit from Griffithsia japonica; AXQ05179.1, γ-subunit from Agarophyton chilense. d, Structural alignment of L RC 1 linker proteins from P. purpureum and G. pacifica in the phycocyanin hexamer showing the bilin \({{\rm{\beta }}}_{2}^{82}\) and the surroundings. The key histidine residue close to the \({{\rm{\beta }}}_{2}^{82}\) PCB is conserved. e, Sequence alignment of L RC 1 from P. purpureum and other red algal and cyanobacterial species. The key histidine residue close to the β82 PCBs is marked with a star. LRC1_GP, L RC 1 from G. pacifica; YP_009294673.1, L RC 1 from red algal G. chorda; YP_007627464.1, L RC 1 from red algal C. crispus; YP_009413376.1, L RC 1 from red algal P. umbilicalis; YP_009244497.1, L RC 1 from red algal A. chilense; WP_006617749.1, L RC 1 from cyanobacteria Arthrospira platensis; WP_009783358.1, L RC 1 from cyanobacteria Lyngbya sp. PCC 8106; WP_017720249.1, L RC 1 from cyanobacteria Oscillatoria sp. PCC 10802; WP_071516454.1, L RC 1 from cyanobacteria Geitlerinema sp. PCC 9228. f, Structural alignment of the L RC 2 and L RC 3 linker proteins from P. purpureum and G. pacifica in the phycoerythrin hexamer proximal to the core showing the bilin \({{\rm{\beta }}}_{2}^{82}\) and the surroundings. Two aromatic residues near to the \({{\rm{\beta }}}_{2}^{82}\) PEB are conserved in both P. purpureum and G. pacifica. g, Sequence alignment of L RC 2–3 from P. purpureum and other red algae. Two aromatic residues close to the β82 PEBs are marked with stars. L RC 2_GP and L RC 3_GP are from G. pacifica. PXF39827.1, XP_005715536.1 and OSX69059.1 are from G. chorda, C. crispus and P. umbilicalis, respectively.