Proteomic analysis of the reaction center-light harvesting 1 complex from Rhodobacter sphaeroides, identifying a previously uncharacterized protein component encoded by a newly-identified ORF.

Photosynthesis in purple bacteria, represented by Rhodobacter sphaeroides as a long-established model organism, utilizes a protein-cofactor complex to capture solar energy. This complex is embedded in specialized spherical membrane structures and comprises a central reaction center (RC) encircled by a ring of light harvesting 1 (LH1) polypeptides. An additional protein PufX has two functions: (1) facilitating ubiquinone/ubiquinol exchange between the RC and membrane and (2) inducing complex dimerization – important for maintaining the curvature of the membrane structures. Cryo-EM has revealed a further component that facilitates dimerization, with proteomic analysis confirming its identity as a previously uncharacterized protein encoded by a newly-identified ORF.