Alterations of the oxygen-evolving apparatus in a 448Arg→448S mutant in the CP47 protein of photosystem II under normal and low chloride conditions

We have shown previously that a mutant which contained the alteration R-448 --> S-448 (R448S) in the CP47 protein of photosystem II exhibited a defect in its ability to grow and assemble functional photosystem. II reaction centers under chloride-limiting conditions [Wu, J., Masri, N., Lee, W., Frankel, L. K., and Bricker, T. M. (1999) Plant Mol. Biol. 39, 381-386]. In this paper we have examined the function of the oxygen-evolving complex under chloride-sufficient (480 muM) and chloride-limiting (< 20 IM) conditions. When placed under chloride-limiting conditions, both the control strain K3 and R448S cells exhibit a loss of steady-state oxygen evolution, with t(1/2) of 16 and 17 min, respectively. Upon the addition of chloride, both recover their oxygen-evolving capacity relatively rapidly. However, R448S exhibits a much slower reactivation of oxygen evolution than does K3 (t(1/2) of 308 and 50 s, respectively). This may indicate a defect at the low-affinity, rapidly exchanging chloride-binding site [Lindberg, K., and Andreasson, L.-E. (1996) Biochemistry 35, 14259-14267]. Additionally, alterations in the distribution of S states and S-state lifetimes were observed. Under chloride-sufficient conditions, the R448S mutant exhibits a significant increase in the proportion of reaction centers in the S-3 state and a greatly increased lifetime of the S-3 state. Under chloride-limiting conditions, the proportion of reaction centers in both the S-2 and S-3 states increases significantly, and there is a marked increase in the lifetime of the S-2 state. These alterations are not observed in the control strain K3. Our observations support the hypothesis that R-448 of CP47 may participate in the formation of the binding domain for chloride in photosystem II and/or in the functional interaction with the 33 kDa protein with the photosystem.