Introduction of the ~(305)Arg→~(305)Ser mutation in the large extrinsic loop E of the CP43 protein of Synechocystis sp. PCC 6803 leads to the loss of cytochrome c_(550) binding to Photosystem II

摘要

CP43, a component of Photosystem II (PSII) in higher plants, algae and cyanobacteria, is encoded by the psbC gene. Previous work demonstrated that alteration of an arginine residue occurring at position 305 to serine produced a strain (R305S) with altered PSII characteristics including lower oxygen-evolving activity, fewer assembled reaction centers, higher sensitivity to photoinactivation, etc. [Biochemistry 38 (1999) 1582]. Additionally, it was determined that the mutant exhibited an enhanced stability of its S_2 state. Recently, we observed a significant chloride effect under chloride-limiting conditions. The mutant essentially lost the ability to grow photoautotrophically, assembled fewer fully functional PS II reaction centers and exhibited a very low rate of oxygen evolution. Thus, the observed phenotype of this mutation is very similar to that observed for the ΔpsbV mutant, which lacks cytochrome c_(550) (Biochemistry 37 (1998) 1551). A His-tagged version of the R305S mutant was produced to facilitate the isolation of PSII particles. These particles were analyzed for the presence of cytochrome c_(550). Reduced minus oxidized difference spectroscopy and chemiluminescence examination of Western blots indicated that cytochrome c_(550) was absent in these PSII particles. Whole cell extracts from the R305S mutant, however, contained a similar amount of cytochrome c_(550) to that observed in the control strain. These results indicate that the mutation R305S in CP43 prevents the strong association of cytochrome c_(550) with the PSII core complex. We hypothesize that this residue is involved in the formation of the binding domain for the cytochrome.