Fig. 4: The features of the RC subunits in Rss. parvum and structural similarities between PufX and N-terminus of the RC-bound Cyt subunits.

a, b The features of the N-terminus of Rss. parvum Cyt subunit. The color codes of αβ-polypeptides are gray, while all other color codes are the same as in Fig. 1. c Superposition of the Cα carbons of RC subunits between Rpi. globiformis (PDB: 7XXF) and the Rss. parvum (this work). The N-terminus of the Cyt subunits of Rss. parvum and Rpi. globiformis are shown by light blue and pale-yellow cartoons, respectively. The other portions of the Rss. parvum RC are colored the same as those in Fig. 1, while those of Rpi. globiformis are colored gray, except for the heme groups, which are shown as yellow sticks. d Expanded view marked in (c) showing that the N-terminal loop region (Met44-Asp65) of the Rss. parvum Cyt subunit overlaps well with that (Phe27-Tyr48) of Rpi. globiformis. For clear presentation, (d) has been slightly rotated relative to the dash box in (c). e Superposition of the Cα carbons of the RC-M subunits between the Rba. sphaeroides monomeric LH1–RC (PDB: 7F0L) and Rss. parvum RC. PufX is shown as a cyan cartoon and the other portions of the complex are shown as gray ribbons, except for Protein-U, which is shown as a hot pink ribbon. f Expanded view marked in (e) showing that the C-terminus (Leu55–Gly69) of PufX overlaps positionally and conformationally with the N-terminal loop region (Met44-Gly58, main chain shown) of the Rss. parvum Cyt subunit.