Is the 9 kDa thylakoid membrane phosphoprotein functionally and structurally analogous to the ‘H’ subunit of bacterial reaction centres?

Packham, Nigel K.

doi:10.1016/0014-5793(88)80835-4

Cited by 27 publications

(11 citation statements)

References 41 publications

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“…Such a role would assume the location of the 9-kDa protein in the close proximity of the D1 protein where it could directly affect the QB site. We have not, however, found sufficient sequence homology between the Synechocystis 6803 PsbH protein and the reaction center H-subunit of purple photosynthetic bacteria to suggest these proteins evolved directly from a common ancestral protein as proposed by Packham (1988).…”

Section: Discussionmentioning

confidence: 80%

Further characterization of the psbH locus of Synechocystis sp. PCC 6803: Inactivation of psbH impairs QA to QB electron transport in photosystem 2

Mayes¹,

Dubbs²,

Vass³

et al. 1993

Biochemistry

101

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The psbH gene encodes a small protein which copurifies with photosystem 2. In the cyanobacterium Synechocystis sp. PCC 6803, psbH is located upstream of the cytochrome b6-f complex genes petC and petA. In striking contrast, in the genomes of plant chloroplasts, psbH is cotranscribed with petB and petD, encoding the other two major subunits of the cytochrome b6-f complex. We report that in Synechocystis sp. PCC 6803 monocistronic psbH and dicistronic petCA transcripts are probably initiated separately, each from DNA regions bearing some similarity to Escherichia coli sigma 70 promoters. Synechocystis sp. PCC 6803 psbH null mutants were generated by cartridge mutagenesis. Studies using a rapid screening procedure involving in situ complementation showed that the PsbH protein is not absolutely required for the assembly of a functionally active photosystem 2 complex since psbH insertion and deletion strains were able to grow photoautotrophically. The rate of photoautotrophic growth was, however, slower than the wild type, and studies of oxygen evolution, chlorophyll fluorescence, and thermoluminescence indicated that this reduction in growth rate is probably due mainly to an impairment in electron flow from QA to QB. We conclude, therefore, that the PsbH protein is not an absolute requirement for photosystem 2 activity but that it functions to optimize electron flow between the two secondary plastoquinone acceptors by interacting with the QB site on the D1 protein.

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Section: Discussionmentioning

confidence: 80%

Further characterization of the psbH locus of Synechocystis sp. PCC 6803: Inactivation of psbH impairs QA to QB electron transport in photosystem 2

Mayes¹,

Dubbs²,

Vass³

et al. 1993

Biochemistry

101

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“…There have been many functions proposed for the phosphorylated form such as protection of the protein from chloroplast aminopeptidases as a means of stabilizing the PSII complex [33]. It has also been suggested that phosphorylation of PSII-H, after having supported plastoquinone interaction and reduction at the QB site, would change the conformation of the QB pocket to reduce plastoquinone binding [35]. Finally, phosphorylation of the PSII-H protein (along with the other Photosystem II proteins) has been proposed to be involved with increasing the charge repulsion against phosphorylated LHC apoproteins, triggering the dissociation of the peripheral antenna complexes and thereby regulating light energy utilization [3,4].…”

Section: Discussionmentioning

confidence: 99%

The psbB gene cluster of the Chlamydomonas reinhardtii chloroplast: sequence and transcriptional analyses of psbN and psbH

Johnson

Schmidt

1993

Plant Mol Biol

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We have sequenced and characterized the complete psbB gene cluster of Chlamydomonas reinhardtii chloroplast DNA. Although the petB and petD genes are located elsewhere, the sequential order of psbB, ORF31, psbN and psbH is identical to that of the psbB operon in higher plants. Also, intergenic non-coding regions are much larger in the Chlamydomonas gene cluster. Northern blot analyses indicate the formation of dicistronic transcripts of psbB and ORF31 and monocistronic transcripts of psbN and psbH. It is unclear whether a psbB operon is transcribed to yield a large polycistronic precursor but northern blot analysis with total RNA from cells grown at 15 degrees C does not detect an increased complexity of the transcripts, as has been found in studies of the psbB operon of higher plants. From primer extension and nuclease protection assays, it is apparent that 5' and 3' processing of the primary psbH transcript results in the accumulation of a heterogenous population of mRNAs. Northern blot analyses reveal transcription of Chlamydomonas psbN and show that its mRNA is much larger than that identified in liverwort and pea. The sequence identities of the PSII-H and PSII-N polypeptides as compared to their vascular plant counterparts is 50 to 62%. While the amino acid sequences of PSII-H and PSII-N proteins are significantly conserved, the mass of PSII-H from Chlamydomonas is significantly larger.

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“…Packham (1988) proposed that PSII-H is the PSII counterpart to the H subunit of reaction centers of photosynthetic www.plantphysiol.org on May 11, 2018 -Published by Downloaded from Copyright © 1997 American Society of Plant Biologists. All rights reserved.…”

Section: Discussionmentioning

confidence: 99%

Requirement for the H Phosphoprotein in Photosystem II of Chlamydomonas reinhardtii

et al. 1997

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To dissect the expression of the psbB gene cluster of the Chlamydomonas reinhardtii chloroplast genome and to assess the role of the photosystem II H-phosphoprotein (PSII-H) in the biogenesis and/or stabilization of PSII, an aadA gene cassette conferring spectinomycin resistance was employed for mutagenesis. Disruption of the gene cluster has no effect on the abundance of transcripts of the upstream psbB/T locus. Likewise, interruption of psbB/T and psbH with a strong transcriptional terminator from the rbcL gene does not influence transcript accumulation. Thus, psbB/T and psbH may be independently transcribed, and the latter gene seems to have its own promoter in C. reinhardtii. In the absence of PSII-H, translation and thylakoid insertion of chloroplast PSII core proteins is unaffected, but PSII proteins do not accumulate. Because the deletion mutant also exhibits PSII deficiency when dark-grown, the effect is unrelated to photoinhibition. Turnover of proteins B and C of PSII and the polypeptides PSII protein A and PSII protein D is faster than in wild-type cells but is much slower than that observed in other PSII-deficient mutants of C. reinhardtii, suggesting a peripheral location of PSII-H in PSII. The role of PSII-H on PSII assembly was examined by sucrose gradient fractionation of pulse-labeled thylakoids; the accumulation of high-molecular-weight forms of PSII is severely impaired in the psbH deletion mutant. Thus, a primary role of PSII-H may be to facilitate PSII assembly/stability through dimerization. PSII-H phosphorylation, which possibly occurs at two sites, may also be germane to its role in regulating PSII structure, stabilization, or activity.

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Is the 9 kDa thylakoid membrane phosphoprotein functionally and structurally analogous to the ‘H’ subunit of bacterial reaction centres?

Cited by 27 publications

References 41 publications

Further characterization of the psbH locus of Synechocystis sp. PCC 6803: Inactivation of psbH impairs QA to QB electron transport in photosystem 2

Further characterization of the psbH locus of Synechocystis sp. PCC 6803: Inactivation of psbH impairs QA to QB electron transport in photosystem 2

The psbB gene cluster of the Chlamydomonas reinhardtii chloroplast: sequence and transcriptional analyses of psbN and psbH

Requirement for the H Phosphoprotein in Photosystem II of Chlamydomonas reinhardtii

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