Identification and Characterization of the SecA Protein Homologue in the Cyanobacterium Synechococcus PCC7942

Nakai, Masaaki; Nohara, Tetsuya; Sugita, Daigo; Endo, Toshiya

doi:10.1006/bbrc.1994.1528

Cited by 45 publications

(47 citation statements)

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“…This is consistent with OE33 transport (20,21) and cytochrome f integration (54, 55) both being SecA-dependent. As with the Rieske protein, there may be sequential interactions between cytochrome f and different stromal factors (i.e.…”

Section: Cp-thylakoid Precursor Protein Interactionssupporting

confidence: 86%

“…In fact, several distinct routes for precursor targeting to the thylakoid membrane have been defined biochemically (15,18) and genetically (19). Particular precursors have been proposed to utilize one of the following pathways: 1) Sec A-dependent (20,21); 2) SRP-dependent (22); 3) ⌬pH-dependent (23, 24); and 4) "spontaneous integration" (25). Pathway selection by a thylakoid lumen-resident precursor seems to be a function of the thylakoid-targeting signal that it bears (26,27).…”

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confidence: 99%

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Chloroplast SRP54 Interacts with a Specific Subset of Thylakoid Precursor Proteins

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Henry

Mould

et al. 1997

Journal of Biological Chemistry

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Signal recognition particles (SRPs) have been identified in organisms as diverse as mycoplasma and mammals; in several cases these SRPs have been shown to play a key role in protein targeting. In each case the recognition of appropriate targeting signals is mediated by SRP subunits related to the 54-kDa protein of mammalian SRP (SRP54). In this study we have characterized the specificity of 54CP, a chloroplast homologue of SRP54 which is located in the chloroplast stroma. We have used a nascent chain cross-linking approach to detect the interactions of 54CP with heterologous endoplasmic reticulum-targeting signals. 54CP functions as a bona fide signal recognition factor which can discriminate between functional and non-functional targeting signals. Using a range of authentic thylakoid precursor proteins we found that 54CP discriminates between thylakoid-targeting signals, interacting with only a subset of protein precursors. Thus, the light-harvesting chlorophyll a/b-binding protein, cytochrome f, and the Rieske FeS protein all showed strong cross-linking products with 54CP. In contrast, no cross-linking to the 23-and 33-kDa proteins of the oxygen-evolving complex were detected. The selectivity of 54CP correlates with the hydrophobicity of the thylakoid-targeting signal and, in the case of light-harvesting chlorophyll a/b-binding protein, with previously determined transport/integration requirements. We propose that 54CP mediates the targeting of a specific subset of precursors to the thylakoid membrane, i.e. those with particularly hydrophobic signal sequences. The signal recognition particle (SRP)1 of mammalian cells is a ribonucleoprotein complex which promotes the signal sequence-dependent targeting of nascent precursor proteins to the endoplasmic reticulum (1-3). Mammalian SRP is composed of six polypeptides and a 7 S RNA, although only one of the polypeptides, the 54-kDa subunit (SRP54), binds to the hydrophobic endoplasmic reticulum (ER)-targeting signals (1-2). Functional homologues of SRP54 have been identified in many organisms and appear relatively conserved during evolution (4, 5). These proteins are usually found complexed with a 7 S-like RNA and the minimum requirement for SRP-dependent protein targeting seems to be a ribonucleoprotein particle composed of an SRP54-like protein and a 7 S-like RNA (6 -8), together with a cognate receptor for the SRP-precursor protein complex (3, 9, 10). Perturbation of SRP-dependent targeting pathways often leads to the accumulation of secretory proteins. However, in many cases only a subset of precursors accumulate while other proteins continue to be secreted normally (9,(11)(12)(13). This suggests that a discrete population of precursors preferentially utilize an SRP-dependent targeting pathway (1, 4, 13).The delivery of precursor proteins to the thylakoid membrane of chloroplasts is governed by thylakoid-targeting signals. These signals are clearly related to those which target proteins to the ER membrane of eukaroytes and the cytoplasmic membrane of prokaryotes....

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Section: Cp-thylakoid Precursor Protein Interactionssupporting

confidence: 86%

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confidence: 99%

Chloroplast SRP54 Interacts with a Specific Subset of Thylakoid Precursor Proteins

High

Henry

Mould

et al. 1997

Journal of Biological Chemistry

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“…Circumstantial evidence exists only for the Sec-dependent pathway, since genes encoding SecA and SecY have been identified in cyanobacterial genomes (Nakai et al, 1992(Nakai et al, , 1994Barbrook et al, 1993). In Escherichia coli, there have been indications also for an signal-recognition particle-dependent transport route (Miller et al, 1994) and a spontaneous membrane integration mechanism (Kuhn et al, 1986) which suggests that these pathways may also exist in cyanobacteria.…”

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confidence: 99%

Transport of CtpA Protein from the Cyanobacterium Synechocystis 6803 Across the Thylakoid Membrane in Chloroplasts

Karnauchov

Herrmann

Pakrasi

et al. 1997

European Journal of Biochemistry

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The CtpA protein in the cyanobacterium Synechocystis 6803 is a C-terminal processing protease that is essential for the assembly of the manganese cluster of the photosystem I1 complex. When fused to different chloroplast-targeting transit peptides, CtpA can be imported into isolated spinach chloroplasts and is subsequently translocated into the thylakoid lumen. Thylakoid transport is mediated by the cyanobacterial signal peptide which demonstrates that the protein transport machinery in thylakoid membranes is functionally conserved between chloroplasts and cyanobacteria. Transport of CtpA across spinach thylakoid membranes is affected by both nigericin and sodium azide indicating that the SecA protein and a transthylakoidal proton gradient are involved in this process. Saturation of the Sec-dependent thylakoid transport route by high concentrations of the precursor of the 33-kDa subunit of the oxygen-evolving system leads to a strongly reduced rate of thylakoid translocation of CtpA which demonstrates transport by the Sec pathway. However, thylakoid transport of CtpA is affected also by excess amounts of the 23-kDa subunit of the oxygen-evolving system, though to a lesser extent. This suggests that the cyanobactenal protein is capable of also interacing with components of the ApH-dependent route and that transport of a protein across the thylakoid membrane may not always be restricted to a single pathway.

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“…A second pathway is utilized by the major light-harvesting chlorophyll-binding protein of PSII and uses a homolog of the signal recognition particle involved in ER protein translocation . A third pathway is followed by a subset of proteins represented by OE33 and plastocyanin and makes use of at least one homolog of the bacterial Sec-dependent secretion pathway (Nakai et al, 1993(Nakai et al, , 1994Yuan et al, 1994). The fourth pathway, which is utilized by proteins such as OE23 and OE17, harvests the energy contained within the energy-rich transmembrane pH gradient to drive proteins across the thylakoid membrane into the lumen.…”

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Analysis of the Import of Carboxyl-Terminal Truncations of the 23-Kilodalton Subunit of the Oxygen-Evolving Complex Suggests That Its Structure Is an Important Determinant for Thylakoid Transport

Roffey

Theg

1996

Plant Physiology

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A series of deletions from the carboxyl terminus of the 23-kD subunit of the photosynthetic oxygen-evolving complex OE23 revealed that these truncations result i n various degrees of inhibition of translocation across thylakoid membranes and their subsequent assembly to the oxygen-evolving complex. lmport of in vitro translated precursors across the chloroplast envelopes was not inhibited by these truncations. Time-course studies of the import of truncated OE23 precursors into intact chloroplasts revealed that the stromal intermediate was subsequently translocated into the thylakoid lumen, where it was processed to a smaller size and rapidly degraded.I n contrast to the full-length OE23 intermediate, the truncated intermediate forms that accumulated in the stroma as a result of de-energization of thylakoid membranes could be found associated with the membrane rather than free in the stroma. Protease digestion experiments revealed that the deletions evidently altered the folded conformation of the protein. These results suggest that the carboxyl-terminal portion of the OE23 precursor is important for the maintenance of an optimal structure for import into thylakoids, implying that the efficient translocation of OE23 requires the protein to be correctly folded. In addition, the rapid degradation of the truncated forms of the processed OE23 within the lumen indicates that a protease (or proteases) active in the lumen can recognize and remove misfolded polypeptides.Within the chloroplast, the multisubunit PSII protein complex is the site of catalysis for the conversion of water to molecular oxygen as a result of photosynthetic electron transfer across thylakoid membranes. The minimal PSII preparation from eukaryotic photosynthetic membranes that is able to catalyze oxygen evolution consists of the 32-and 34-kD integral protein subunits known as D1 and D2, which make up the core of the reaction center; the a and p subunits of Cyt b559; the core antenna components CP43 and CP47; and severa1 other small polypeptides (reviewed by Debus, 1992;Vermaas, 1993). Most oxygen-evolving preparations also contain a 33-kD extrinsic protein (OE33), although its presence is not strictly required for this activity. Two additional extrinsic protein components of 23 and 17 kD (OE23 and OE17) also are associated with a more intact oxygen-evolving membrane preparation. The extrinsic subunits of the OEC, OE33,OE23, and OE17 are tightly bound to the lumen-exposed domains of the PSII complex. Loss of the OE23 and OE17 proteins has been correlated with lowered rates of oxygen evolution, but because depleted membranes retain the ability to catalyze water oxidation, these polypeptides are considered to have structural and regulatory roles, as opposed to catalytic functions, in oxygen evolution (Vermaas, 1993).The assembly of the OEC is of interest not only for its implications in mechanistic and regulatory aspects of oxygen evolution, but also because the multimeric PSII-OEC is formed with subunits encoded by both chloroplast and nuclear genes...

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Identification and Characterization of the SecA Protein Homologue in the Cyanobacterium Synechococcus PCC7942

Cited by 45 publications

References 0 publications

Chloroplast SRP54 Interacts with a Specific Subset of Thylakoid Precursor Proteins

Chloroplast SRP54 Interacts with a Specific Subset of Thylakoid Precursor Proteins

Transport of CtpA Protein from the Cyanobacterium Synechocystis 6803 Across the Thylakoid Membrane in Chloroplasts

Analysis of the Import of Carboxyl-Terminal Truncations of the 23-Kilodalton Subunit of the Oxygen-Evolving Complex Suggests That Its Structure Is an Important Determinant for Thylakoid Transport

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