Protein W: a PufX-like protein from Rhodopseudomonas palustris?

The recent crystal structure of the reaction centre-light harvesting 1 (RC-LH1) core complex from the purple bacterium Rhodopseudomonas (Rps.) palustris (Roszak et al., unpublished data) shows the complex to consist of an elliptical LH1 ring that surrounds the RC. The LH1 ring is interrupted at a position adjacent to the QB binding site of the RC by a single membrane spanning polypeptide. This small polypeptide, which has been christened protein W, is suggested to act in a manner analogous to the PufX protein of Rhodobacter (Rb.) sphaeroides and Rb. capsulatus to allow the migration of ubiquinol from the RC to the Q-pool. Here, we report on the identification, purification and characterisation of protein W from Rps. palustris.