Expression of Anabaena PCC 7937 plastocyanin in Synechococcus PCC 7942 enhances photosynthetic electron transfer and alters the electron distribution between photosystem I and cytochrome-c oxidase.
The petE gene encoding plastocyanin precursor protein from the cyanobacterium Anabaena PCC 7937 was introduced in the cyanobacterial host strain Synechococcus PCC 7942. The host normally only uses cytochrome c553 as Photosystem I (PS I) donor. The heterologous gene was efficiently expressed using the inducible Escherichia coli trc promoter. Accumulation of plastocyanin protein depended on the presence of Cu2+. The protein was accurately targeted to the thylakoid lumen, from which it could be isolated in the mature form. Redox difference spectroscopy proved the presence of a Cu2+ ion in the holoenzyme. Isolated heterologous plastocyanin was functional in reconstitution of in vitro electron transfer to PS I. The presence of Anabaena plastocyanin in Synechococcus thylakoid membranes increased PS I electron transfer rate 2.5 times. Analysis of P700 redox and PS II fluorescence transients in vivo showed a faster electron transfer through PS I because of enhanced electron supply in the presence of plastocyanin. In addition, the distribution of electrons between photosynthetic and respiratory electron transfer changed. Plastocyanin preferentially donates electrons to PS I rather than to the respiratory cytochrome-c oxidase complex and is not functionally equivalent to cytochrome c553.
Department of Molecular Cell Biology, University of Utrecht, The Netherlands.
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D
Geerts
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Schubert
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de Vrieze
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Borrias
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Matthijs
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Weisbeek
D017033:Anabaena / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000378:metabolism*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli; D018014:Gene Transfer Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045331:Photosystem I Protein Complex; D010970:Plastocyanin / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D013045:Species Specificity
D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010970:Plastocyanin; D003576:Electron Transport Complex IV