Synthesis and characterization of de novo designed peptides modelling the binding sites of [4Fe–4S] clusters in photosystem I

Abstract

Photosystem I (PS I) converts the energy of light into chemical energy via transmembrane charge separation. The terminal electron transfer cofactors in PS I are three low-potential [4Fe–4S] clusters named F X, F A and F B, the last two are bound by the PsaC subunit. We have modelled the F A and F B binding sites by preparing two apo-peptides (maquettes), sixteen amino acids each. These model peptides incorporate the consensus [4Fe–4S] binding motif along with amino acids from the immediate environment of the iron–sulfur clusters F A and F B. The [4Fe–4S] clusters were successfully incorporated into these model peptides, as shown by optical absorbance, EPR and Mössbauer spectroscopies. The oxidation–reduction potential of the iron–sulfur cluster in the F A-maquette is − 0.44 ± 0.03 V and in the F B-maquette is − 0.47 ± 0.03 V. Both are close to that of F A and F B in PS I and are considerably more negative than that observed for other [4Fe–4S] model systems described earlier (Gibney, B. R., Mulholland, S. E., Rabanal, F., and Dutton, P. L. Proc. Natl. Acad. Sci. U.S.A. 93 (1996) 15041–15046). Our optical data show that both maquettes can irreversibly bind to PS I complexes, where PsaC-bound F A and F B were removed, and possibly participate in the light-induced electron transfer reaction in PS I.