Insights into the binding behavior of native and non-native cytochromes to photosystem I from Thermosynechococcus elongatus

Abstract

The binding of photosystem I (PS I) from to the native cytochrome (cyt) and cyt from horse heart (cyt) was analyzed by oxygen consumption measurements, isothermal titration calorimetry (ITC), and rigid body docking combined with electrostatic computations of binding energies. Although PS I has a higher affinity for cyt than for cyt, the influence of ionic strength and pH on binding is different in the two cases. ITC and theoretical computations revealed the existence of unspecific binding sites for cyt besides one specific binding site close to P Binding to PS I was found to be the same for reduced and oxidized cyt Based on this information, suitable conditions for cocrystallization of cyt with PS I were found, resulting in crystals with a PS I:cyt ratio of 1:1. A crystal structure at 3.4-Å resolution was obtained, but cyt cannot be identified in the electron density map because of unspecific binding sites and/or high flexibility at the specific binding site. Modeling the binding of cyt to PS I revealed a specific binding site where the distance and orientation of cyt relative to P are comparable with cyt from purple bacteria relative to P This work provides new insights into the binding modes of different cytochromes to PS I, thus facilitating steps toward solving the PS I-cyt costructure and a more detailed understanding of natural electron transport processes.

Non-detergent isolation of a cyanobacterial photosystem I using styrene maleic acid alternating copolymers

“…Further, this shielding effect is more pronounced for divalent ions compared to monovalent ions of equivalent ionic strength, suggesting the ability of Mg 2+ can bridge negative charges on PSI sidechains. 88 We conclude that the decrease in reduction kinetics for PSI-SMALP and PSI-DDM in this buffer system are attributed to elevated pH and a lack of divalent ions, not the absence of the PsaF subunit ( Fig. 7A and B).…”

“…Recently in Te, binding energy between PSI and cyt 6 has been shown to be repulsive at low ionic strength and pH 8. 84,88 Kölsch et al demonstrate that this repulsion is caused in part by negatively charged side chains on the lumenal loop of PsaA and cyt 6 . Further, this shielding effect is more pronounced for divalent ions compared to monovalent ions of equivalent ionic strength, suggesting the ability of Mg 2+ can bridge negative charges on PSI sidechains.…”

“…The non-specic binding and lack of native electrostatics driving the interaction of these two proteins explains why the buffer effect seen with native cty 6 is absent in this experiment. 88 However, the fact that mitigating this variable allows for the reduction of PSI in the SMALP at nearly twice the rate as PSI-DDM may suggest that the translocation of the high energy electron through the protein complex following photoexcitation may be faster in the SMALP compared to DDM isolation, further investigation is needed to evaluate this hypothesis.…”

A precursor-approach in constructing 3D ITO electrodes for the improved performance of photosystem I-cyt c photobioelectrodes

“…Here, PSI-cyt c system could be transferred onto 3D inverse opal micro-ITO electrodes, in which high photocurrents could be achieved due to high loadings; however, the heterogeneous electron transfer constant was smaller than for the gold electrodes. 84 Insights into interactions between cyt c and PSI have been also provided in the study of Kölsch et al 297 In the study of Feifel et al, cyt c combination with enzymes has been investigated, and two enzymes, cellobiose dehydrogenase and laccase have been immobilized…”

Photosystem I Multilayers within Porous Indium Tin Oxide Cathodes Enhance Mediated Electron Transfer

“…Many strategies have been explored with aims of maximizing electron transfer between PSI and its host electrode . To enable DET, monolayers of PSI protein complexes have been coupled with various linking molecules and proteins, which help minimize the electrode‐protein separation distance and also provide an energetically favorable pathway for electron transfer . Most notably, the cytochrome complex (cyt c) has been used to attach PSI onto a variety of electrode materials …”