Fig. 4: Interactions of CpcL with the bilins β⁸² at the bottom trimer of CpcL-PBS.

a–d Bottom view of CpcL-PBS, showing the CpcL (green) and the three β⁸² bilins, ^1Iβ⁸²₁ (square b), ^1Iβ⁸²₂ (square c), and ^1Iβ⁸²₂ (square d), of CpcL-PBS. Interaction of key amino acid residues of CpcL (green) with ^1Iβ⁸²₁ (panel b) ^1Iβ⁸²₂ (panel c) and ^1Iβ⁸²₃ (panel d). The bilins (open chain tetrapyrrole) are in pink with the four pyrrole rings labeled A through D. Oxygen atoms are in red, nitrogen atoms are in blue. The dashed lines indicate interactions and the distances between the atoms are in Angstroms. e Structural comparison of bilin ^1Iβ⁸²₂ from CpcG-PBS rod (PDB 7SC8)¹³ and CpcL-PBS. Alignment was done with the CpcB subunit as reference, and the RMSD of all non-hydrogen atoms on the ring D is 0.5 Å between two bilins. f Structural comparison of CpcG-CpcB (PDB 7SC8) and CpcL-CpcB complexes by aligning their subunit CpcB. The environment around bilin ^1Iβ⁸²₂ is highlighted in brown solid rectangle box. g Zoom-in view of the environment around bilin ^1Iβ⁸²₂. The difference between CpcL and CpcG lies in α6 and α7 helices. h A 45° rotated view of (g). The distance between the residues that regulate the conformation of their bilin ^1Iβ⁸²₂ are highlighted in red. i Residues that are responsible for modulating the conformation of this α6-α7 region.