Association of protochlorophyllide with the PufQ protein of Rhodobacter capsulatus

The PufQ protein, prepared by the recombinant expression of the pufQ gene of Rhodobacter capsulatus, has been reconstituted into liposomes in the presence of the bacteriochlorophyll precursor, protochlorophyllide. The liposomes were separated from liposomes free of the PufQ protein by sucrose density gradient ultracentrifugation and analyzed for their content of protochlorophyllide, protein, and phospholipid. The results indicated a 3.5 times higher level of association of protochlorophyllide with the PufQ protein-containing liposomes than with liposomes containing either the hydrophobic protein, apolipoprotein A-I, or the water-soluble maltose-binding protein. Only the association of the protochlorophyllide with the PufQ protein corresponded to a small but reproducible shift in its fluorescence emission maximum to a lower wavelength, consistent with a change in its environment.