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

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We have shown previously that a mutant which contained the alteration 448R → 448S (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., Mash, 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 μM) and chloride-limiting (<20 μM) conditions. When placed under chloride-limiting conditions, both the control strain K3 and R448S cells exhibit a loss of steady-state oxygen evolution, with t1/2 of 16 and 17 rain, 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 (t1/2 of 308 and 50 s, respectively). This may indicate a defect at the low-affinity, rapidly exchanging chloride-binding site [Lindberg, K., and Andréasson, 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 S3 state and a greatly increased lifetime of the S3 state. Under chloride-limiting conditions, the proportion of reaction centers in both the S2 and S3 states increases significantly, and there is a marked increase in the lifetime of the S2 state. These alterations are not observed in the control strain K3. Our observations support the hypothesis that 448R 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.

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