Structural Organization of Photosystem I Polypeptides

Xu, Qiang; Chitnis, Vaishali P.; An, Kuznetsov; Chitnis, Parag R.

doi:10.1007/978-94-009-0173-5_251

Cited by 9 publications

(8 citation statements)

References 10 publications

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“…Thermolysin is well suited for this purpose because it is highly active at starch-gelatinization temperatures, and has also been shown to effectively hydrolyze hydrophobic proteins located at the surfaces of chloroplasts and other subcellular organelles (Cline et al, 1984;Xu and Chitnis, 1995). Upon extended incubation of intact starch granules with thermolysin at subgelatinization temperatures, we found that zeins were selectively removed from the starch granule surface.…”

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confidence: 62%

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Surface Localization of Zein Storage Proteins in Starch Granules from Maize Endosperm1

Mu-Forster

Wasserman

1998

Plant Physiology

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Starch granules from maize (Zea mays) contain a characteristic group of polypeptides that are tightly associated with the starch matrix (C. Mu-Forster, R. Huang, J.R. Powers, R.W. Harriman, M. Knight, G.W. Singletary, P.L. Keeling, B.P. Wasserman [1996] Plant Physiol 111: 821-829). Zeins comprise about 50% of the granule-associated proteins, and in this study their spatial distribution within the starch granule was determined. Proteolysis of starch granules at subgelatinization temperatures using the thermophilic protease thermolysin led to selective removal of the zeins, whereas granule-associated proteins of 32 kD or above, including the waxy protein, starch synthase I, and starch-branching enzyme IIb, remained refractory to proteolysis. Granule-associated proteins from maize are therefore composed of two distinct classes, the surface-localized zeins of 10 to 27 kD and the granule-intrinsic proteins of 32 kD or higher. The origin of surface-localized delta-zein was probed by comparing delta-zein levels of starch granules obtained from homogenized whole endosperm with granules isolated from amyloplasts. Starch granules from amyloplasts contained markedly lower levels of delta-zein relative to granules prepared from whole endosperm, thus indicating that delta-zein adheres to granule surfaces after disruption of the amyloplast envelope. Cross-linking experiments show that the zeins are deposited on the granule surface as aggregates. In contrast, the granule-intrinsic proteins are prone to covalent modification, but do not form intermolecular cross-links. We conclude that individual granule intrinsic proteins exist as monomers and are not deposited in the form of multimeric clusters within the starch matrix.

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confidence: 62%

“…Hydrolysis was conducted at 64°C, or as indicated, for defined intervals, and reactions were terminated by the addition of EDTA to 20 mm (Cline et al, 1984;Xu and Chitnis, 1995). Starch granules were recovered by centrifugation at 13,000g for 5 min.…”

Section: Protease Digestion Of Starch Granulesmentioning

confidence: 99%

Surface Localization of Zein Storage Proteins in Starch Granules from Maize Endosperm1

Mu-Forster

Wasserman

1998

Plant Physiology

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“…Each figure is representative of two independent determinations. per P700 reaction center (Xu et al, 1995;Chitnis, 1996). In addition, the PSI complex contains approximately 100 chlorophyll a molecules, several ␤-carotene molecules, two phylloquinone molecules, and three [4Fe-4S] clusters.…”

Section: Discussionmentioning

confidence: 99%

Characterization of Two Photosynthetic Mutants of Maize1

1999

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We describe here the biochemical characteristics of the hcf44 and hcf47 (high chlorophyll fluorescence) mutants of maize (Zea mays L.). Both mutants were sensitive to high light intensities, exhibiting reduced growth and fluorescence intensity. Electron transport through the mutants' photosystem (PS) I and PSII reaction centers was reduced and NADP ؉ photoreduction was absent. Western analysis revealed that the hcf44 mutant was missing some or all of the PsaC, PsaD, and PsaE polypeptides of the PSI reaction center, and reverse transcriptase-polymerase chain reaction demonstrated that this loss was the result of a posttranscriptional event. The hcf47 mutant had reduced levels of many PSI and PSII polypeptides. These data indicate a possible defect in the synthesis or assembly of the PsaC subunit in the hcf44 mutant, whereas the hcf47 mutant may have a more general defect in the biogenesis of photosynthetic membranes. Our results demonstrate the coordinated assembly of the peripheral proteins into the PSI complexes of higher plants and demonstrate the in vivo requirement of PsaC, PsaD, and PsaE subunits for the function of PSI in higher plants.

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“…This result indicates that the mutant PsaD subunit has a lower affinity to the PSI complexes. PsaD interacts with PsaC, PsaL, and the extramembrane loops of PsaB (Xu et al, 1994a(Xu et al, , 1995aArmbrust et al, 1996;Jansson et al, 1996;Sun et al, 199%). Among these interactions, we propose that PsaD-PsaC interactions are not altered by the mutations based on the following results.…”

Section: Discussionmentioning

confidence: 99%

The PsaD Subunit of Photosystem I (Mutations in the Basic Domain Reduce the Level of PsaD in the Membranes)

Chitnis

1997

Plant Physiology

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The PsaD subunit of photosystem I (PSI) is a peripheral protein that provides a docking site for ferredoxin and interacts with the PsaB, PsaC, and PsaL subunits of PSI. We used site-directed mutagenesis to determine the function of a basic region in PsaD of the cyanobacterium Synechocystis sp. PCC 6803. We generated five mutant strains in which one or more charged residues were altered. Western blotting showed that replacement of lysine (Lys)-74 with glutamine or glutamic acid led to a substantial decrease in the level of PsaD in the membranes. The mutant PSI complexes showed reduced NADP+ photoreduction activity mediated by ferredoxin; the decrease in activity correlated with the reduced level of PsaD. Using protein synthesis inhibitors we showed that the degradation rates of the mutant and wild-type PsaD were similar, indicating a defect in the assembly of the mutant protein. Treatment of the mutant PSI complexes with a different concentration of Nal showed that the mutations decreased affinity between PsaD and the transmembrane components of PSI. With glutaraldehyde, the mutant and wild-type PsaD proteins could be cross-linked with PsaC, but the PsaD-PsaL cross-linked product was reduced drastically when arginine-72, Lys-74, and Lys-76 were mutated simultaneously. These studies demonstrate that the basic residues in the central region of PsaD, especially Lys-74, are crucial in the assembly of PsaD into the PSI complex.

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Structural Organization of Photosystem I Polypeptides

Cited by 9 publications

References 10 publications

Surface Localization of Zein Storage Proteins in Starch Granules from Maize Endosperm1

Surface Localization of Zein Storage Proteins in Starch Granules from Maize Endosperm1

Characterization of Two Photosynthetic Mutants of Maize1

The PsaD Subunit of Photosystem I (Mutations in the Basic Domain Reduce the Level of PsaD in the Membranes)

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