Structural Basis of Efficient Electron Transport between Photosynthetic Membrane Proteins and Plastocyanin in Spinach Revealed Using Nuclear Magnetic Resonance

Abstract

In the photosynthetic light reactions of plants and cyanobacteria, plastocyanin (Pc) plays a crucial role as an electron carrier and shuttle protein between two membrane protein complexes: cytochrome b 6 f (cyt b 6 f) and photosystem I (PSI). The rapid turnover of Pc between cyt b 6 f and PSI enables the efficient use of light energy. In the Pc-cyt b 6 f and Pc-PSI electron transfer complexes, the electron transfer reactions are accomplished within <10 24 s. However, the mechanisms enabling the rapid association and dissociation of Pc are still unclear because of the lack of an appropriate method to study huge complexes with short lifetimes. Here, using the transferred cross-saturation method, we investigated the residues of spinach (Spinacia oleracea) Pc in close proximity to spinach PSI and cyt b 6 f, in both the thylakoid vesicle-embedded and solubilized states. We demonstrated that the hydrophobic patch residues of Pc are in close proximity to PSI and cyt b 6 f, whereas the acidic patch residues of Pc do not form stable salt bridges with either PSI or cyt b 6 f, in the electron transfer complexes. The transient characteristics of the interactions on the acidic patch facilitate the rapid association and dissociation of Pc.

Transition metals in plant photosynthesis

“…Mutational analyses in Pc from spinach have revealed that the hydrophobic residues surrounding the Cu 2+ /Cu + ion, such as Leu12 and Ala90 and the acidic residues located adjacent to the hydrophobic patch, such as Asp42, Glu43, Asp44, Glu45, Glu59, Glu60, and Asp61 are important for Pc-PSI electron transport in eukaryotic plants [39][40][41][42][43][44] and Pc-cyt b 6 f. 32,40,45,46 The hydrophobic patch residues of Pc are in close proximity to PSI and cyt b 6 f complex, whereas the acidic patch residues of Pc do not form stable salt bridges with either PSI or cyt b 6 f complex, in the electron transfer complexes. 47 The transient characteristics of the interactions on the acidic patch facilitate the rapid association and dissociation of Pc.…”

Nanodomains of Cytochromeb 6 fand Photosystem II Complexes in Spinach Grana Thylakoid Membranes

“…An NMR study of the complex between cytochrome f and plastocyanin from the cyanobacterium Nostoc showed that the binding interface involves hydrophobic residues with charged residues at the edge (Díaz-Moreno et al, 2005). A more recent NMR study of the Pc-cytb 6 f interaction using spinach components, including SG membranes, showed that there is an initial, loose electrostatic interaction and the subsequent formation of an electron transfer complex relies on hydrophobic interactions (Ueda et al, 2012).…”

NMR as a tool to investigate the structure, dynamics and function of membrane proteins

“…56 This method has been applied to identify the precise binding interface between a chemokine and the GPCR CXCR4 or plastocyanin and photosynthetic membrane proteins and provides mechanistic insight into these respective interactions. 57–58 More traditional NMR chemical shift perturbation and resonance line-broadening approaches have been employed to detect the interaction of arrestin with rhodopsin. 59 Since ssNMR methods have no principle limitations on size, both protein partners can be directly observed by exploring creative isotope labeling strategies in combination with specific ssNMR pulse schemes.…”