Introduction of the 305Arg→305Ser mutation in the large extrinsic loop E of the CP43 protein of Synechocystis sp PCC 6803 leads to the loss of cytochrome c550 binding to Photosystem II

CP43, a component of Photosystem 11 (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 11 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 DeltapsbV 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. (C) 2002 Elsevier Science B.V. All rights reserved.