In Situ Effects of Mutations of the Extrinsic Cytochrome c550 of Photosystem II in Synechocystis sp. PCC6803
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- 作者：Zhaoliang Li ; Heather Andrews ; Julian J. Eaton-Rye ; and Robert L. Burnap
- 刊名：Biochemistry
- 出版年：2004
- 出版时间：November 9, 2004
- 年：2004
- 卷：43
- 期：44
- 页码：14161 - 14170
- 全文大小：255K
- 年卷期：v.43,no.44(November 9, 2004)
- ISSN：1520-4995
文摘
The H2O oxidizing domain of the cyanobacterial photosystem II (PSII) complex contains alow potential, c-type cytochrome termed c550 that is essential for the in vivo stability of the PSII complex.A mutant lacking cytochrome c550 (
psbV) in Synechocystis sp. PCC6803 has been further analyzed togetherwith a construct in which the distal axial heme iron ligand, histidine 92, has been substituted with amethionine (C550-H92M). Heme staining of SDS-PAGE showed that the C550-H92M mutation didnot disturb the accumulation and heme-binding properties of the cytochrome. In psbV cells, the numberof charge separating PSII centers was estimated to be 56% of the wild type, but of the existing centers,33% lacked photooxidizable Mn ions. C550-H92M did not discernibly affect the intrinsic PSII electron-transfer kinetics compared to the wild type nor did it exhibit a significant fraction of centers lackingphotooxidizable Mn; however, the number of charge separating PSII centers in mutant cells was 69% ofthe wild type. C550-H92M lost photoautotrophic growth ability in the absence of Ca2+, but its growthwas not affected by depletion of Cl-, which differs from psbV. Taken together, the results suggest thatin the absence of cytochrome c550 electron transfer on the donor side is retarded perhaps at the level ofYz to P680+ transfer, the heme ligand. His92 is not absolutely required for assembly of functional PSIIcenters; however, replacement by methionine prevents normal accumulation of PSII centers in the thylakoidmembranes and alters the Ca2+ requirement of PSII. The results are discussed in terms of currentunderstanding of the Ca2+ site of PSII.
psbV) in Synechocystis sp. PCC6803 has been further analyzed togetherwith a construct in which the distal axial heme iron ligand, histidine 92, has been substituted with amethionine (C550-H92M). Heme staining of SDS-PAGE showed that the C550-H92M mutation didnot disturb the accumulation and heme-binding properties of the cytochrome. In psbV cells, the numberof charge separating PSII centers was estimated to be 56% of the wild type, but of the existing centers,33% lacked photooxidizable Mn ions. C550-H92M did not discernibly affect the intrinsic PSII electron-transfer kinetics compared to the wild type nor did it exhibit a significant fraction of centers lackingphotooxidizable Mn; however, the number of charge separating PSII centers in mutant cells was 69% ofthe wild type. C550-H92M lost photoautotrophic growth ability in the absence of Ca2+, but its growthwas not affected by depletion of Cl-, which differs from psbV. Taken together, the results suggest thatin the absence of cytochrome c550 electron transfer on the donor side is retarded perhaps at the level ofYz to P680+ transfer, the heme ligand. His92 is not absolutely required for assembly of functional PSIIcenters; however, replacement by methionine prevents normal accumulation of PSII centers in the thylakoidmembranes and alters the Ca2+ requirement of PSII. The results are discussed in terms of currentunderstanding of the Ca2+ site of PSII.