Mutation of Phe-363 in the photosystem II protein CP47 impairs photoautotrophic growth, alters the chloride requirement, and prevents photosynthesis in the absence of either PSII-O or PSII-V in Synechocystis sp. PCC 6803

The deletion of the amino acids between Gly-351 and Thr-365 within the larg e, lumen-exposed, hydrophilic region (loop E) of the photosystem IT (PSII) chlorophyll a-binding protein CP47 produced a strain of Synechocystis sp. P CC 6803 that failed to assemble stable PSII centers [Eaton-Rye, J. J., and Vermaas, W. F. J. (1991) Plant Mel. Biol. 17, 1165-1177]. The importance of two conserved Phe residues at positions 362 and 363 within this deletion h as been investigated. The F363R strain had impaired photoautotrophic growth and an enhanced sensitivity to photoinactivation, demonstrating that Phe i s required at position 363 for normal PSII function. In contrast, photoauto trophic growth in strains N361K and F362R was unaffected. Uniquely, among t he mutant strains tested, F363R was unable to grow under chloride-limiting conditions, and this effect was reversed by replacing chloride with bromide . The removal of the manganese-stabilizing protein (PSII-O), the 12 kDa ext rinsic protein (PSII-U), and cytochrome c-550 (PSII-V) was investigated in each mutant in vivo. In N361K and F362R, removal of PSII-V produced a more deleterious effect than the removal of PSII-O, but even so, all strains rem ained photoautotrophic. In contrast, the absence of PSII-V and PSII-O in F3 63R produced obligate photoheterotrophic strains. The removal of PSII-U inc reased the susceptibility of PSII to heat inactivation and further decrease d the stability of PSII in F363R, demonstrating that PSII-U can contribute to the stabilization of mutations that have been introduced into CP47. The order of importance of the selective removal of the extrinsic proteins in s trains carrying mutations in loop E of CP47 was found to be as follows: Del ta PSII-V greater than or equal to Delta PSII-O > Delta PSII-U.