Organization of PSI Subunits in Thylakoid Membranes

Zilber, April; Wynn, R. Max; Webber, Andrew N.; Malkin, Richard

doi:10.1007/978-94-009-0511-5_352

Cited by 6 publications

(7 citation statements)

References 8 publications

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“…The 17.8-kD band that partitioned into the hydrophobic phase in Triton X-1 14 extraction experiments (36) is probably the intrinsic PSI-L subunit. The cleavage site is located in the loop between the second and third proposed transmembrane spans, indicating that this loop is stroma-exposed.…”

Section: Psi-ementioning

confidence: 96%

Organization and Topology of Photosystem I Subunits

Zilber¹,

Malkin²

1992

Plant Physiol.

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Intact spinach (Spinacia oleracea) thylakoid membranes were treated with various proteases and photosystem I (PSI) complexes were isolated from these membranes to define the membrane topology of specific PSI subunits. Trypsin treatment caused cleavage of the PSI-D and E subunits. Thermolysin treatment cleaved the PSI-D, E, H, and K subunits, and also caused limited degradation of the reaction center core PSI-A and B subunits. Pronase treatment produced the most dramatic results as the PSI-A and B subunits were cleaved to 47-, 45-, 26-, and 24-kilodalton products. In addition, pronase degraded the PSI-D, E, H, K, and L subunits. Proteolytic cleavage sites for several of the products were identified by amino acid sequencing. The results indicate that PSI-A, B, D, E, H, K, and L subunits all have stroma-exposed regions, and these findings are summarized in a model describing the subunit organization of PSI.

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Section: Psi-ementioning

confidence: 96%

Organization and Topology of Photosystem I Subunits

Zilber¹,

Malkin²

1992

Plant Physiol.

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“…8c, lane 3). Taken together, these results indicate that all the epitopes for the PSI-D antibodies probably lie between resi-exposure on the stromal surface of the membrane [7, 36, 71. In the case of PSI-D, tryptic cleavage after Lys-15 was also reported [37]. However, great care should be exercised in interpreting the results of proteolysis experiments in terms of inside/outside localization.…”

Section: Epitopes Mapping and Proteolysismentioning

confidence: 97%

Purification and membrane topology of PSI‐D and PSI‐E, two subunits of the photosystem I reaction center

Lagoutte

Valloni

1992

European Journal of Biochemistry

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Structural studies have been conducted on polypeptides PSI-D and PSI-E, whch are extrinsic but firmly bound to the photosystem I reaction center. These subunits are predicted to be involved in the correct interaction with soluble electron acceptor(s), like ferredoxin. We designed an original method to extract both polypeptides directly from thylakoid membranes and to purify them: a stepwise extraction with NaSCN followed by size fractionation and reverse-phase HPLC. Investigation of the in situ topology of PSI-D and PSI-E was undertaken using monoclonal antibody binding, controlled proteolysis, peptide sequencing and electron microscopy. The precise identification of numerous proteolytic sites indicates that the entire N-terminal regions of PSI-E (up to Glu15) and PSI-D (up to LyslS) are exposed to the medium. Partial mapping of the exposed epitopes was possible using purified fragments of each polypeptide. In the case of PSI-E, this mapping confirmed the accessibility of the N-terminal part, and suggested the need for another exposed sequence, probably located after Met39 in the second half of the protein. For PSI-D, this mapping revealed that the sequence between Met74 and Metl40, including the most basic amino acid clusters, is also partly accessible. These experiments provide the first detailed informations, although still partial, on the topology of these polypeptides. They give a preliminary basis for hypotheses concerning the sites of interaction with the soluble counterparts.

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“…Extraction of a membrane-protein by Triton X-114 or organic solvents depends on the overall hydrophobicity of the protein. Spinach PsaF partitions with Triton-X 114, indicating its hydrophobic nature (Zilber et al 1990;Tjus and Andersson 1991). The amino acid sequences of PsaF deduced from the gene sequences reveal two 27 moderately hydrophobic regions in this protein (Chitnis et al 1991).…”

Section: Psafmentioning

confidence: 99%

“…Biochemical studies have shown that two large subunits (PsaA and PsaB) and some low molecular weight subunits (PsaF, PsaL, PsaK, PsaG, PsaI, PsaJ, and PsaM) are integral membrane-proteins with highly hydrophobic transmembrane domains (Ortiz et al 1985;Zilber et al 1990;Tjus and Andersson 1991;Xu et al 1994c,e). PsaD, PsaC, PsaE, and PsaH are peripheral proteins on the stromal (cytoplasmic) side of photosynthetic membranes (Li et al 1991 a;Tjus and Andersson 1991;Lagoutte and Vallon 1992).…”

Section: Topology Of the Psi Complexmentioning

confidence: 99%

Function and organization of Photosystem I polypeptides

Chitnis

et al. 1995

Photosynth Res

119

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Photosystem I functions as a plastocyanin:ferredoxin oxidoreductase in the thylakoid membranes of chloroplasts and cyanobacteria. The PS I complex contains the photosynthetic pigments, the reaction center P700, and five electron transfer centers (A0, A1, FX, FA, and FB) that are bound to the PsaA, PsaB, and PsaC proteins. In addition, PS I complex contains at least eight other polypeptides that are accessory in their functions. Recent use of cyanobacterial molecular genetics has revealed functions of the accessory subunits of PS I. Site-directed mutagenesis is now being used to explore structure-function relations in PS I. The overall architecture of PSI complex has been revealed by X-ray crystallography, electron microscopy, and biochemical methods. The information obtained by different techniques can be used to propose a model for the organization of PS I. Spectroscopic and molecular genetic techniques have deciphered interaction of PS I proteins with the soluble electron transfer partners. This review focuses on the recent structural, biochemical and molecular genetic studies that decipher topology and functions of PS I proteins, and their interactions with soluble electron carriers.

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Organization of PSI Subunits in Thylakoid Membranes

Cited by 6 publications

References 8 publications

Organization and Topology of Photosystem I Subunits

Organization and Topology of Photosystem I Subunits

Purification and membrane topology of PSI‐D and PSI‐E, two subunits of the photosystem I reaction center

Function and organization of Photosystem I polypeptides

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