Light-dependent D1 protein synthesis and translocation is regulated by reaction center II. Reaction center II serves as an acceptor for the D1 precursor.

N Adir,S Shochat,I Ohad

doi:10.1016/s0021-9258(19)38381-4

N Adir, S Shochat + Show 1 more

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https://doi.org/10.1016/s0021-9258(19)38381-4

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Abstract

Light induces an irreversible modification of the photosystem II reaction center (RCII) affecting specifically one of its major components, the D1 protein (Ohad, I., Adir, N., Koike, H., Kyle, D. J., and Inoue, Y. I. (1990) J. Biol. Chem. 265, 1972-1979) which is degraded and replaced continuously (turnover). The turnover rate of D1 is related to light intensity. Evidence is presented showing that RCII translocates from the site of damage in the grana (appressed) domain of the chloroplast membranes to unappressed membrane domains where the D1 precursor protein (pD1) is translated and becomes integrated into RCII. Several forms of RCII (a, a*, and b) were identified on the basis of their electrophoretic mobility. pD1 was found only in the a and b forms in the unappressed membranes. Processing of pD1 occurs after its integration into RCII. Mature D1 appeared mostly in the a form of RCII and following its translocation to the appressed membrane domains also in the a* form. Thus the light intensity-dependent synthesis of D1 protein is related to the availability of modified RCII which serves as an acceptor for pD1. The shuttling of RCII between the two membrane domains may represent a control mechanism of thylakoid membrane protein synthesis.

Highlights

In cells exposed to growth light intensity, most of the RCII is localized in the granal fraction as detected by antibodies against the 47-kDa Dl and D2 polypeptides (Fig. 1, control lanes)
Based on the data presented in this work we propose that following its light-induced modification [6, 12], RCII dissociates in uiuo from the light-harvesting antennae in the granal membrane domain [23] as an assembled complex and appears to translocate to the unappressed membrane domains where it serves as an acceptor for the newly synthesized pD1
The contention that light enhances translocation of RCII to the unappressed membrane regions as an assembled complex is essential to this conclusion and is based on the fact that neither pD1 nor the Dl, D2, or 47-kDa polypeptides of RCII could be detected as free running polypeptides in the second dimension electrophoresis

Summary

Introduction

The turnover rate of Dl is related to light intensity. Evidence is presented showing that RCII translocates from the site of damage in the grana (appressed) domain of the chloroplast membranes to unappressed membrane domains where the Dl precursor protein (pD1) is translated and becomes integrated into RCII. The light intensity-dependent synthesis of Dl protein is related to the availability of modified RCII which serves as an acceptor for pD1. The shuttling of RCII between the two membrane domains may represent a control mechanism of thylakoid membrane protein synthesis. The chloroplast-encoded Dl protein of the photosystem II reaction center (RCII)’ [1, 2] turns over in the light, but not in the dark, in higher plants [3] and in green algae [4]. The light-dependent degradation of Dl does not require simultaneous synthesis (4, ll), and the two processes

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