Synthesis and Assembly of the D1 Protein into Photosystem II: Processing of the C-Terminus and Identification of the Initial Assembly Partners and Complexes during Photosystem II Repair

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• 作者：Klaas J. van Wijk ; Margrit Roobol-Boza ; Reetta Kettunen ; Bertil Andersson ; and Eva-Mari Aro
• 刊名：Biochemistry
• 出版年：1997
• 出版时间：May 20, 1997
• 年：1997
• 卷：36
• 期：20
• 页码：6178 - 6186
• 全文大小：287K
• 年卷期：v.36,no.20(May 20, 1997)
• ISSN：1520-4995

文摘

In previous studies [van Wijk, K. J., Bingsmark, S.,Aro, E.-M., & Andersson, B. (1995) J.Biol. Chem. 270, 25685-25695; van Wijk, K. J., Andersson, B., &Aro, E.-M. (1996) J. Biol. Chem 271,9627-9636], we have demonstrated that D1 protein synthesized inisolated chloroplasts and thylakoidsis incorporated into the photosystem II (PSII) core complex. Bypulse-chase experiments in these invitro systems, followed by sucrose gradient fractionation ofsolubilized thylakoid membranes, it was shownthat this assembly proceeded stepwise; first the D1 protein wasincorporated to form a PSII reactioncenter complex (PSII rc), and through additional assembly steps thePSII core complex was formed. Inthis study, we have analyzed this assembly process in more detail, withspecial emphasis on the initialevents, through further purification and analysis of the assemblyintermediates by nondenaturing Deriphat-PAGE and by flatbed isoelectric focusing. The D2 protein was foundto be the dominant PSII reactioncenter protein initially associating with the new D1 protein. Thisstrongly suggests that the D2 proteinis the primary "receptor" or stabilizing component during ordirectly after synthesis of the D1 protein.After formation of the D1-D2 heterodimer, cytb₅₅₉ became attached, whereas thepsbI gene product wasassembled as a subsequent step, thereby forming a PSII reaction centercomplex. Subsequent formationof the PSII core occurred by binding of CP47 and then CP43 to the PSIIrc. The rapid radiolabeling ofa minor population of a PSII core subcomplex without CP43 indicatedthat an association of newlysynthesized D1 protein with a preexisting complex consisting of D2/cytb₅₅₉/psbI gene product/CP47waspossibly occurring, in parallel to the predominant sequential assemblypathway. The kinetics of synthesisand processing of the precursor D1 protein were followed in isolatedchloroplasts and were comparedwith its incorporation into PSII assembly intermediates. Noprecursor D1 protein was found in PSII corecomplexes, indicating either that incorporation into the PSII corecomplex facilitates the cleavage of theC-terminus or, more likely, that processing is more rapid than theassembly into the PSII core.