Functional and Structural Analyses of the Rhodobacter capsulatus PufX Protein

The pufX gene of Rhodobacter capsulatus was discovered from DNA sequence analysis as an orf (originally designated C2397) that codes for a 78 amino acid protein, located 3’ of the reaction center (RC) M gene (the pufM gene) [1]. Investigations of RNA messages revealed that the orf C2397 is transcribed, and so it was designated as the pufX gene [2]. A pufX deletion mutant strain was constructed and its properties were compared with those of an otherwise isogenic pufX+ strain [3]. The results of growth studies, biochemical and biophysical experiments, DNA sequence analyses of second site mutations that suppress the effects of pufX mutations, and evaluation of photosynthetic complex structures were used to formulate a model of the PufX protein function. In this model the R. capsulatus PufX protein was proposed to be a component of a light harvesting (LHI) ring that surrounds the RC, to facilitate quinone exchange between the quinone pool and the RC [4].