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An intermediate membrane subfraction in cyanobacteria is involved in an assembly network for Photosystem II biogenesis.

ABSTRACT: Early steps in the biogenesis of Photosystem II (PSII) in the cyanobacterium Synechocystis sp. PCC 6803 are thought to occur in a specialized membrane fraction that is characterized by the specific accumulation of the PSII assembly factor PratA and its interaction partner pD1, the precursor of the D1 protein of PSII. Here, we report the molecular characterization of this membrane fraction, called the PratA-defined membrane (PDM), with regard to its lipid and pigment composition and its association with PSII assembly factors, including YCF48, Slr1471, Sll0933, and Pitt. We demonstrate that YCF48 and Slr1471 are present and that the chlorophyll precursor chlorophyllide a accumulates in the PDM. Analysis of PDMs from various mutant lines suggests a central role for PratA in the spatial organization of PSII biogenesis. Moreover, quantitative immunoblot analyses revealed a network of interdependences between several PSII assembly factors and chlorophyll synthesis. In addition, formation of complexes containing both YCF48 and Sll0933 was substantiated by co-immunoprecipitation experiments. The findings are integrated into a refined model for PSII biogenesis in Synechocystis 6803.

SUBMITTER: Rengstl B

PROVIDER: S-EPMC3122249 | biostudies-literature | 2011 Jun

REPOSITORIES: biostudies-literature

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An intermediate membrane subfraction in cyanobacteria is involved in an assembly network for Photosystem II biogenesis.

Rengstl Birgit B Oster Ulrike U Stengel Anna A Nickelsen Jörg J

The Journal of biological chemistry 20110429 24

Early steps in the biogenesis of Photosystem II (PSII) in the cyanobacterium Synechocystis sp. PCC 6803 are thought to occur in a specialized membrane fraction that is characterized by the specific accumulation of the PSII assembly factor PratA and its interaction partner pD1, the precursor of the D1 protein of PSII. Here, we report the molecular characterization of this membrane fraction, called the PratA-defined membrane (PDM), with regard to its lipid and pigment composition and its associati ...[more]

PMID: 21531723

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Project description:Oxygen (O2), a dominant element in the atmosphere and an essential molecule for most life on Earth, is produced by the photosynthetic oxidation of water. However, metabolic activity can cause the generation of reactive O2 species (ROS) that can damage lipids, proteins, nucleic acids, and threaten cell viability. To identify and characterize mechanisms that allow cells to cope with the potentially negative effects of O2 reactivity, we performed a high-throughput O2 sensitivity screen on a genome-wide insertional mutant library of the unicellular alga Chlamydomonas reinhardtii. This screen led to the identification of several genes that, when disrupted, alter the cell's sensitivity to O2 in the light. One of these genes encodes a protein designated Rubisco methyltransferase 2 (RMT2). Although this protein has homology to methyltransferases, it has not yet been demonstrated to catalyze methyltransferase reactions. Furthermore, the rmt2 mutant has not been observed to be compromised for the level of Rubisco (first enzyme of Calvin-Benson Cycle; CBC), although the mutant cells were light sensitive, which is reflected by a marked decrease in the level of photosystem I (PSI), with much less of an impact on the other photosynthetic complexes; this mutant also shows upregulation of genes encoding the Ycf3 and Ycf4 proteins, which are associated with the biogenesis of PSI. The RMT2 protein has a chloroplast targeting sequence predicted by PredAlgo and PB-Chlamy1,2, and rescue of the mutant with a wild-type (WT) copy of the gene fused to the mNeonGreen fluorophore indicates that the protein is within the chloroplast and appears to be enriched in/around the pyrenoid (an intrachloroplast compartment, potentially hypoxic, that is found in many algae that contain the CO2-fixing enzyme Rubisco), but we also observe it more dispersed throughout the stroma. These results suggest that RMT2 may serve an important role in the biogenesis of PSI and that PSI biogenesis may be enriched around or within the pyrenoid, which may reflect the impact of O2/reactive O2 species on the efficiency with which PSI can assemble.

Dataset Information

An intermediate membrane subfraction in cyanobacteria is involved in an assembly network for Photosystem II biogenesis.

Publications

An intermediate membrane subfraction in cyanobacteria is involved in an assembly network for Photosystem II biogenesis.

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