The Rieske Fe/S protein of the cytochrome b6/f complex in chloroplasts: missing link in the evolution of protein transport pathways in chloroplasts?
The Rieske Fe/S protein, a nuclear-encoded subunit of the cytochrome b(6)/f complex in chloroplasts, is retarded in the stromal space after import into the chloroplast and only slowly translocated further into the thylakoid membrane system. As shown by the sensitivity to nigericin and to specific competitor proteins, thylakoid transport takes place by the DeltapH-dependent TAT pathway. The Rieske protein is an untypical TAT substrate, however. It is only the second integral membrane protein shown to utilize this pathway, and it is the first authentic substrate without a cleavable signal peptide. Transport is instead mediated by the NH(2)-terminal membrane anchor, which lacks, however, the twin-arginine motif indicative of DeltapH/TAT-dependent transport signals. Furthermore, transport is affected by sodium azide as well as by competitor proteins for the Sec pathway in chloroplasts, demonstrating for the first time some cross-talk of the two pathways. This might take place in the stroma where the Rieske protein accumulates after import in several complexes of high molecular mass, among which the cpn60 complex is the most prominent. These untypical features suggest that the Rieske protein represents an intermediate or early state in the evolution of the thylakoidal protein transport pathways.
Molik
S
S
Institut für Pflanzenphysiologie, Martin-Luther-Universität Halle-Wittenberg, Weinbergweg 10, D-06120 Halle (Saale), Germany.
Karnauchov
I
I
Weidlich
C
C
Herrmann
R G
RG
Klösgen
R B
RB
D020816:Amino Acid Motifs; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001667:Binding, Competitive; D060365:Chloroplast Proteins; D002736:Chloroplasts / Q000378:metabolism*; D003573:Cytochrome b Group / Q000378:metabolism*; D045346:Cytochrome b6f Complex; D014450:Electron Transport Complex III; D019143:Evolution, Molecular; D006863:Hydrogen-Ion Concentration; D007506:Iron-Sulfur Proteins / Q000378:metabolism* / Q000502:physiology*; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000378:metabolism; D009550:Nigericin / Q000494:pharmacology; D010940:Plant Proteins; D011485:Protein Binding; D021381:Protein Transport; D018724:Spinacia oleracea / Q000378:metabolism; D020524:Thylakoids / Q000378:metabolism
D000900:Anti-Bacterial Agents; D060365:Chloroplast Proteins; D003573:Cytochrome b Group; D007506:Iron-Sulfur Proteins; D008565:Membrane Proteins; D010940:Plant Proteins; C037989:Rieske iron-sulfur protein; D045346:Cytochrome b6f Complex; D014450:Electron Transport Complex III; D009550:Nigericin