The solution structure of the PufX polypeptide from Rhodobacter sphaeroides

PufX organises the photosynthetic reaction centre–light harvesting complex 1 (RC–LH1) core complex of Rhodobacter sphaeroides and facilitates quinol/quinone exchange between the RC and cytochrome bc₁ complexes. The structure of PufX in organic solvent reveals two hydrophobic helices flanked by unstructured termini and connected by a helical bend. The proposed location of basic residues and tryptophans at the membrane interface orients the C-terminal helix along the membrane normal, with the GXXXG motifs in positions unsuitable as direct drivers of dimerisation of the RC–LH1 complex. The N-terminal helix is predicted to extend 40 Å along the membrane interface.