Light-stimulated degradation of an unassembled Rieske FeS protein by a thylakoid-bound protease: the possible role of the FtsH protease.
Unassembled subunits of the cytochrome b6f complex as well as components of other unassembled chloroplastic complexes are rapidly degraded within the organelle. However, the mechanisms involved in these proteolytic processes are obscure. When the Rieske FeS protein (RISP) is imported into isolated chloroplasts in vitro, some of the protein does not property assemble with the cytochrome complex, as determined by its sensitivity to exogenous protease. When assayed in intact, lysed, or fractionated chloroplasts, the imported RISP was found to be sensitive to endogenous proteases as well. The activity responsible for degradation of the unassembled protein was localized to the thylakoid membrane and characterized as a metalloprotease requiring zinc ions for its activity. The degradation rate was stimulated by light, but no involvement of ATP or redox control was observed. Instead, when the RISP that was attached to thylakoid membranes was first illuminated on ice, degradation proceeded in either light or darkness at equal rates suggesting a light-induced conformational change making the protein prone to degradation. Antibodies raised against native FtsH, a bacterial, membrane-bound, ATP-dependent, zinc-stimulated protease, effectively inhibited degradation of the unassembled RISP, suggesting a role for the chloroplastic FtsH in this process.
Ostersetzer
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Department of Agricultural Botany, Hebrew University of Jerusalem, Rehovot, Israel.
Adam
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D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism; D003573:Cytochrome b Group / Q000378:metabolism; D045346:Cytochrome b6f Complex; D014450:Electron Transport Complex III; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D008027:Light; D008565:Membrane Proteins / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000378:metabolism; D018532:Pisum sativum; D010940:Plant Proteins / Q000378:metabolism; D011487:Protein Conformation; D012639:Seeds; D013696:Temperature; D015032:Zinc / Q000378:metabolism
D001426:Bacterial Proteins; D003573:Cytochrome b Group; D007506:Iron-Sulfur Proteins; D008565:Membrane Proteins; D010940:Plant Proteins; C037989:Rieske iron-sulfur protein; D045346:Cytochrome b6f Complex; D008666:Metalloendopeptidases; D000251:Adenosine Triphosphatases; D014450:Electron Transport Complex III; D015032:Zinc