Amino acid deletions in loop C of the chlorophyll a-binding protein CP47 alter the chloride requirement and/or prevent the assembly of photosystem II

The chlorophyll a-binding protein CP47 directs excitation energy to the rea ction center of photosystem II (PSII) during oxygenic photosynthesis and ha s additional structural and functional roles associated with the PSII water -oxidizing complex. Oligonucleotide-directed mutagenesis was employed to st udy loop C of CP47 (approximately Trp-162 to Gly-197) which faces the thyla koid lumen. Five short amino acid deletion strains, Delta (S169-P171), Delt a (Y172-G176), Delta (G176-P180), Delta (E184-A188) and Delta (F190-N194), were created that span this domain. The deletion between Gly-176 and Pro-18 0, located around the middle of loop C, produced an obligate photoheterotro ph that could not assemble functional PSII centers. The deletions in mutant s Delta (S169-P171) and Delta (Y172-G176) reduced PSII levels to less than or equal to 20% of the control and thus impaired photoautotrophic growth. I n contrast, mutants Delta (E184-A188) and Delta (F190-N194) were photoautot rophic even though the number of photosystems was decreased by 50%. All PSI I complexes assembled in the deletion strains had an increased susceptibili ty to photoinactivation and deletion of Glu-184 to Ala-188 prevented photoa utotrophic growth under chloride-limiting conditions. Furthermore, the remo val of the extrinsic PSII-O, PSII-U and PSII-V proteins from mutants Delta (E184-A188) and Delta (F190-N194) reduced the rates of oxygen evolution and , in the strains lacking either the PSII-O or PSII-V proteins, also increas ed the photoautotrophic doubling times. These effects were greater in mutan t Delta (E184-A188) than in mutant Delta (F190-N194) and the order of impor tance for the removal of the extrinsic proteins was found to be Delta PSII- V greater than or equal to Delta PSII-O > Delta PSII-U.