INVOLVEMENT OF THE CP47 PROTEIN IN STABILIZATION AND PHOTOACTIVATION OF A FUNCTIONAL WATER-OXIDIZING COMPLEX IN THE CYANOBACTERIUM SYNECHOCYSTIS SP PCC-6803

Oscillation patterns of the oxygen yield per flash induced by a train of single-turnover flashes were measured as a function of dark incubat ion and different pre-illumination conditions in several autotrophic m utant strains of Synechocystis sp. PCC 6803 carrying short deletions w ithin the large, lumen-exposed hydrophilic region (loop E) of the chlo rophyll a-binding photosystem II protein CP47. A physiological and bio chemical characterization of these mutant strains has been presented p reviously [Eaton-Rye, J. J., and Vermaas, W. F. J. (1991) Plant Mel. B iol. 17, 1165-1177; Haag, E., Eaten-Rye, J. J., Renger, G., and Vermaa s, W. F. J. (1993) Biochemistry 32, 4444-4454], and some functional pr operties were described recently [Gleiter, H. M., Haag, E., Shen, J.-R ., Eaten-Rye, J. J., Inoue, Y., Vermaas, W. F. J., and Renger, G. (199 4) Biochemistry 33, 12063-12071]. The present study shows that in seve ral mutants the water-oxidizing complex (WOC) became inactivated durin g prolonged dark incubation, whereas the WOC of the wild-type strain r emained active. The rate and extent of the inactivation in the mutants depend on the domain of loop E, where 3-8 amino acid residues were de leted. The most pronounced effects are observed in mutants Delta(A373- D380) and Delta(R384-V392). A competent WOC can be restored from the f ully inactivated state by illumination with short saturating flashes. The number of flashes required for this process strongly depends on th e site at which a deletion has been introduced into loop E. Again, the most prominent effects were found in mutants Delta(A373-D380) and Del ta(R384-V392). Interestingly, the number of flashes required for activ ation was reduced by more than an order of magnitude in both mutants b y the addition of 10 mM CaCl2 to the cell suspension. On the basis of a model for photoactivation proposed by Tamura and Cheniae (1987) [Bio chim. Biophys. Acta 890, 179-193], a scheme is presented for the proce sses of dark; inactivation and photoactivation in these mutants. The r esults presented here corroborate an important role of the large hydro philic domain (loop E) of CP47 in a functional and stable WOC.