The atypical iron-coordination geometry of cytochrome f remains unchanged upon binding to plastocyanin, as inferred by XAS

Abstract

The transient complex between cytochrome f and plastocyanin from the cyanobacterium Nostoc sp. PCC 7119 has been analysed by X-ray Absorption Spectroscopy in solution, using both proteins in their oxidized and reduced states. Fe K-edge data mainly shows that the atypical metal coordination geometry of cytochrome f, in which the N-terminal amino acid acts as an axial ligand of the heme group, remains unaltered upon binding to its redox partner, plastocyanin. This fact suggests that cytochrome f provides a stable binding site for plastocyanin and minimizes the reorganization energy required in the transient complex formation, which could facilitate the electron transfer between the two redox partners.Keywords Cytochrome f AE Electron transfer AE Metalloproteins AE Plastocyanin AE Transient complexes AE X-ray absorption spectroscopy Abbreviations Cf water-soluble fragment of cytochrome f ET electron transfer EXAFS extended X-ray absorption fine structure FT Fourier transform Pc plastocyanin XANES X-ray absorption near edge structure XAS X-ray absorption spectroscopy XRD X-Ray diffraction DE 0 internal potential correction Dr change in the distance between the metal and ligand atoms r Debye-Waller parameter related to the system dynamic disorder

The cytochrome f–plastocyanin complex as a model to study transient interactions between redox proteins

“…The cyanobacterial Nostoc C f –Pc complex has been analyzed by X‐ray absorption spectroscopy (XAS). Both Fe and Cu K‐edge XAS measurements of free and bound redox proteins have been studied in solution, using either the oxidized or reduced species [42,43].…”

Electrostatic strain and concerted motions in the transient complex between plastocyanin and cytochrome f from the cyanobacterium Phormidium laminosum

“…Force field parameters corresponding to the oxidised copper site were those developed by Comba and Remenyi [38]. For the reduced heme moiety, Banci's parameters [39] were used, and a harmonic force of 200 kcal mol − 1 Å − 2 -with an equilibrium distance of 2.44 Å -was applied to the bond between Fe and the N terminus of Cf acting as the sixth ligand, to account for the stiffness of this bond observed by X-ray absorption values [40]. Counter-ions were added and all systems were solvated with TIP3P water molecules [41] (see Table SI-1 in Supplementary information), using the TLEAP module of AMBER.…”