Reconstitution of barley photosystem I with modified PSI-C allows identification of domains interacting with PSI-D and PSI-A/B

Helle Naver, M. Paul Scott, John H. Golbeck, Birger L. Møller, Henrik V. Scheller

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42 Scopus citations


The PSI-C subunit of photosystem I shows similarity to soluble 2[4Fe-4S] ferredoxins. Alignment analysis clearly shows that PSI-C contains an 8- residue internal loop and a 15-residue C-terminal extension that are absent in the ferredoxins. The remaining residues in PSI-C are likely to be folded in a way similar to the soluble 2[4Fe-4S] ferredoxins. Two modified PSI-C subunits lacking either the 8-residue loop or 10 residues of the C terminus were expressed in Escherichia coli and used to reconstitute a barley P700- F(X) core prepared to specifically lack PSI-C, PSI-D, and PSI-E. As shown by EPR spectroscopy, the modified proteins carry two [4Fe-4S] clusters with characteristics similar to those of native PSI-C. Western blot analysis of the reconstituted photosystem I complexes showed that the modified PSI-C proteins bind to the P700-F(X) core. Flash photolysis revealed that in photosystem I complexes reconstituted in the presence of PSI-D with the C- terminally deleted PSI-C, the F(A)/F(B) back-reaction was less efficiently restored than with wild-type PSI-C. The loop-deleted PSI-C was even less efficient. We attribute these differences to altered binding properties of the modified proteins. Comparison of reconstitutions performed in the presence and absence of PSI-D shows that the loop-deleted PSI-C is unable to bind without PSI-D, whereas the C-terminally deleted PSI-C binds only weakly with PSI-D. These results imply that the internal loop of PSI-C interacts with the PSI-A/B heterodimer and that the C terminus of PSI-C interacts with PSI-D.

Original languageEnglish (US)
Pages (from-to)8996-9001
Number of pages6
JournalJournal of Biological Chemistry
Issue number15
StatePublished - Apr 12 1996

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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