Demonstration of the Key Role Played by the PufX Protein in the Functional and Structural Organization of Native and Hybrid Bacterial Photosynthetic Core Complexes

The role of a component of the bacterial photosystem, the PufX protein, was examined by heterologous expression of thepufX gene fromRhodobacter capsulatus in a strain ofR. sphaeroides that lacks the nativepufX gene. The strain ofR. sphaeroides containing theR. capsulatus PufX protein was capable of efficient transduction of light energy despite a low degree of sequence conservation between the PufX proteins from the two species. The organization of the hybrid reaction center/LH1 photosystem in strains ofR. sphaeroides containing theR. capsulatus LH1 antenna complex was affected differently by theR. sphaeroides andR. capsulatus PufX proteins. We discuss the implications of our findings for the role of the PufX protein in organizing the bacterial photosystem for efficient transduction of light energy.