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A Domain of the Manganese-stabilizing Protein fromSynechococcus elongatus Involved in Functional Binding to Photosystem II*

Site-directed mutagenesis was performed to investigate whether the two protease-sensitive sequences Phe156-Gly163 and Arg184-Ser191, of the manganese-stabilizing protein (MSP) from a thermophilic cyanobacterium, Synechococcus elongatus (Motoki, A., Shimazu, T., Hirano, M., and Katoh, S. (1998) Biochim. Biophys. Acta 1365, 492–502), are involved in functional interaction with photosystem II (PSII). The ability of MSP to bind to its functional site on the PSII complex and to reactivate oxygen evolution was dramatically reduced by the substitution of Arg152, Asp158, Lys160, or Arg162 with uncharged residues, by insertion of a single residue between Phe156 and Leu157, or by deletion of Leu157. Substitution of each of the four charged residues with an identically charged residue showed that the charges at Asp158, and possibly Lys160, are important for the electrostatic interaction with PSII. The reactivating ability was also strongly affected by the alteration of Phe156 to Leu. Replacement of Lys188, the only strictly conserved charged residue in the Arg184–Ser191 sequence, by Gln had only a marginal effect on the function of MSP. High affinity binding of MSP to PSII was also affected significantly by mutation at Arg152, which is located in a region (Val148–Arg152) strictly conserved among the 14 sequences so far reported. These results imply that the Val148–Gly163 sequence, which is well conserved among MSPs from cyanobacteria to higher plants, is a domain of MSP for functional interaction with PSII.