Tuning Radical Relay Residues by Proton Management Rescues Protein Electron Hopping

Yee, Estella F.; Dzikovski, Boris; Crane, Brian R.

doi:10.1021/jacs.9b05715

Cited by 14 publications

(11 citation statements)

References 179 publications

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“…[ 50–52 ] Tryptophan is an oxidizable aromatic residue whose redox activity is involved in photosynthetic water splitting, nucleic acid biosynthesis, and cell signaling, acting as a hole carrier. It plays a major role in proton‐coupled electron transfer, [ 53,54 ] and mediates photoinduced long‐range ET in photolyase [ 55,56 ] and in dye‐modified Az mutants. [ 57,58 ] In plants cryptochrome, the ET rate is modified by two orders of magnitude by ATP binding and by pH modulating the electronic coupling of a Trp residue.…”

Section: Resultsmentioning

confidence: 99%

Distance and Potential Dependence of Charge Transport Through the Reaction Center of Individual Photosynthetic Complexes

López-Ortiz

Zamora

Giannotti

et al. 2021

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Charge separation and transport through the reaction center of photosystem I (PSI) is an essential part of the photosynthetic electron transport chain. A strategy is developed to immobilize and orient PSI complexes on gold electrodes allowing to probe the complex's electron acceptor side, the chlorophyll special pair P700. Electrochemical scanning tunneling microscopy (ECSTM) imaging and current–distance spectroscopy of single protein complex shows lateral size in agreement with its known dimensions, and a PSI apparent height that depends on the probe potential revealing a gating effect in protein conductance. In current–distance spectroscopy, it is observed that the distance‐decay constant of the current between PSI and the ECSTM probe depends on the sample and probe electrode potentials. The longest charge exchange distance (lowest distance‐decay constant β) is observed at sample potential 0 mV/SSC (SSC: reference electrode silver/silver chloride) and probe potential 400 mV/SSC. These potentials correspond to hole injection into an electronic state that is available in the absence of illumination. It is proposed that a pair of tryptophan residues located at the interface between P700 and the solution and known to support the hydrophobic recognition of the PSI redox partner plastocyanin, may have an additional role as hole exchange mediator in charge transport through PSI.

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Section: Resultsmentioning

confidence: 99%

Distance and Potential Dependence of Charge Transport Through the Reaction Center of Individual Photosynthetic Complexes

López-Ortiz

Zamora

Giannotti

et al. 2021

Small

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“…These findings should have far-reaching implications for biological ET reactions. For instance, the redox-active residues, especially Tyr and Trp, , are widely involved in biologically important proteins such as PSII, ,,− Ribonucleotide reductase (RNR), − LPMO, , and peroxidases. ,, In these proteins, the redox-active Tyr or Trp residues usually have H-bonding interactions with adjacent basic residues (e.g., Asp, Glu, His). In such cases, the adjacent base may mediate the ET/PCET process or stabilize the cation radical intermediate via H-bonding interactions. ,− Such a regulation would depend on the p K a of redox-active residues.…”

Section: Discussionmentioning

confidence: 99%

Understanding the Key Roles of pH Buffer in Accelerating Lignin Degradation by Lignin Peroxidase

Fang

Feng

Jiang

et al. 2023

JACS Au

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pH buffer plays versatile roles in both biology and chemistry. In this study, we unravel the critical role of pH buffer in accelerating degradation of the lignin substrate in lignin peroxidase (LiP) using QM/MM MD simulations and the nonadiabatic electron transfer (ET) and proton-coupled electron transfer (PCET) theories. As a key enzyme involved in lignin degradation, LiP accomplishes the oxidation of lignin via two consecutive ET reactions and the subsequent C−C cleavage of the lignin cation radical. The first one involves ET from Trp171 to the active species of Compound I, while the second one involves ET from the lignin substrate to the Trp171 radical. Differing from the common view that pH = 3 may enhance the oxidizing power of Cpd I via protonation of the protein environment, our study shows that the intrinsic electric fields have minor effects on the first ET step. Instead, our study shows that the pH buffer of tartaric acid plays key roles during the second ET step. Our study shows that the pH buffer of tartaric acid can form a strong H-bond with Glu250, which can prevent the proton transfer from the Trp171-H •+ cation radical to Glu250, thereby stabilizing the Trp171-H •+ cation radical for the lignin oxidation. In addition, the pH buffer of tartaric acid can enhance the oxidizing power of the Trp171-H •+ cation radical via both the protonation of the proximal Asp264 and the second-sphere H-bond with Glu250. Such synergistic effects of pH buffer facilitate the thermodynamics of the second ET step and reduce the overall barrier of lignin degradation by ∼4.3 kcal/mol, which corresponds to a rate acceleration of 10 3 -fold that agrees with experiments. These findings not only expand our understanding on pH-dependent redox reactions in both biology and chemistry but also provide valuable insights into tryptophanmediated biological ET reactions.

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“…For instance, the redox-active residues, especially Tyr and Trp, 96,97 are widely involved in biologically important proteins such as PSII, 2,4,14,15,98,99 Ribonucleotide reductase (RNR), [100][101][102] LPMO, 103,104 and peroxidases. 102,105,106 In these proteins, the redox-active Tyr or Trp residues usually form H-bonding interactions with adjacent bases (e.g. Asp, Glu, His).…”

Section: Discussionmentioning

confidence: 99%

pH Accelerates the Long-Range Electron Transfer for Lignin Degradation via Second-Sphere H-Bonding Interactions

Fang

Feng

Jiang

et al. 2022

Preprint

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pH plays versatile roles in both biology and chemistry. For instance, pH can regulate the long-range electron transfer (ET) in many proteins. However, the mechanistic basis of many pH-dependent long-range ET processes remain unclear. In this study, we unravel the critical role of pH in accelerating the long-range ET in lignin peroxidase (LiP) using QM/MM MD simulations and the nonadiabatic ET and PCET theories. As a key enzyme involved in lignin degradation, LiP accomplishes the one-electron oxidation of lignin via two consecutive long-range ET reactions: the first one involves ET from Trp171 to the active species of Compound I, affording the Trp171 radical species, while the second one involves ET from the lignin substrate to the Trp171 radical, affording the lignin cation radical species. Our study demonstrates that pH can remarkably modulate the mechanism and kinetics of both ET reactions. Specifically, in the absence of the pH buffer of tartaric acid, our study shows that the first ET leads to a neutral Trp• radical, agreeing with the EPR experiments. Surprisingly, the addition of the tartaric acid stabilizes the Trp-H•+ cation radical via second-sphere H-bonding interactions and accelerates the ET rate for lignin oxidation by several orders of magnitude. These findings are consistent with the experimental information available, which not only expand our understanding on pH-dependent ET reactions in both biology and chemistry, but also provide valuable insights on tryptophan-mediated biological ET reactions.

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Tuning Radical Relay Residues by Proton Management Rescues Protein Electron Hopping

Cited by 14 publications

References 179 publications

Distance and Potential Dependence of Charge Transport Through the Reaction Center of Individual Photosynthetic Complexes

Distance and Potential Dependence of Charge Transport Through the Reaction Center of Individual Photosynthetic Complexes

Understanding the Key Roles of pH Buffer in Accelerating Lignin Degradation by Lignin Peroxidase

pH Accelerates the Long-Range Electron Transfer for Lignin Degradation via Second-Sphere H-Bonding Interactions

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