Two functionally distinct manganese clusters formed by introducing a mutation in the carboxyl terminus of a photosystem II reaction center polypeptide, D1, of the green alga Chlamydomonas reinhardtii.
To study the function of the carboxyl-terminal domain of a photosystem II (PSII) reaction center polypeptide, D1, chloroplast mutants of the green alga Chlamydomonas reinhardtii have been generated in which Leu-343 and Ala-344 have been simultaneously or individually replaced by Phe and Ser, respectively. The mutants carrying these replacements individually, L343F and A344S, showed a wild-type phenotype. In contrast, the double mutant, L343FA344S, evolved O2 at only 20-30% of the wild-type rate and was unable to grow photosynthetically. In this mutant, PSII accumulated to 60% of the wild-type level, indicating that the O2-evolving activity per PSII was reduced to approximately half that of the wild-type. However, the amount of Mn atom detected in the thylakoids suggested that a normal amount of Mn cluster was assembled. An investigation of the kinetics of flash-induced fluorescence yield decay revealed that the electron transfer from Q(-)(A) to Q(B) was not affected. When a back electron transfer from Q(-)(A) to a donor component was measured in the presence of 3-(3,4-dichlorophenol)-1,1-dimethylurea, a significantly slower component of the Q(-)(A) oxidation was detected in addition to the normal component that corresponds to the back electron transfer from the Q(-)(A) to the S(2)-state of the Mn cluster. Thermoluminescence measurements revealed that L343FA344S cells contained two functionally distinct Mn clusters. One was equivalent to that of the wild-type, while the other was incapable of water oxidation and was able to advance the transition from the S(1)-state to the S(2)-state. These results suggested that a fraction of the Mn cluster had been impaired by the L343FA344S mutation, leading to decreased O2 evolution. We concluded that the structure of the C-terminus of D1 is critical for the formation of the Mn cluster that is capable of water oxidation, in particular, transition to higher S-states.
Hatano-Iwasaki
A
A
Department of Biology, Faculty of Science, Okayama University, Japan.
Minagawa
J
J
Inoue
Y
Y
Takahashi
Y
Y
D000818:Animals; D016825:Chlamydomonas reinhardtii; D000460:Chlorophyta / Q000737:chemistry* / Q000235:genetics; D004579:Electron Transport; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008163:Luminescent Measurements; D008345:Manganese / Q000737:chemistry*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010455:Peptides / Q000737:chemistry*; D010641:Phenotype; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics; D045332:Photosystem II Protein Complex
D010455:Peptides; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D008345:Manganese