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 reaction center of photosystem II (PSII) during oxygenic photosynthesis and has additional structural and functional roles associated with the PSII water-oxidizing complex. Oligonucleotide-directed mutagenesis was employed to study loop C of CP47 (approximately Trp-162 to Gly-197) which faces the thylakoid lumen. Five short amino acid deletion strains, delta(S169-P171), delta(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-180, located around the middle of loop C, produced an obligate photoheterotroph that could not assemble functional PSII centers. The deletions in mutants delta(S169-P171) and delta(Y172-G176) reduced PSII levels to < or = 20% of the control and thus impaired photoautotrophic growth. In contrast, mutants delta(E184-A188) and delta(F190-N194) were photoautotrophic even though the number of photosystems was decreased by 50%. All PSII complexes assembled in the deletion strains had an increased susceptibility to photoinactivation and deletion of Glu-184 to Ala-188 prevented photoautotrophic growth under chloride-limiting conditions. Furthermore, the removal 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 increased the photoautotrophic doubling times. These effects were greater in mutant delta(E 184-A188) than in mutant delta(F190-N194) and the order of importance for the removal of the extrinsic proteins was found to be deltaPSII-V > or = deltaPSII-O > deltaPSII-U.