Properties of the high‐spin heme of MauG are altered by binding of preMADH at the protein surface 40 Å away

The diheme enzyme MauG catalyzes oxidative post-translational modifications of a protein substrate, precursor protein of methylamine dehydrogenase (preMADH), that binds to the surface of MauG. The high-spin heme iron of MauG is located 40 Å from preMADH. The ferric heme is an equilibrium of five- and six-coordinate states. PreMADH binding increases the proportion of five-coordinate heme three-fold. On reaction of MauG with H2O2 both hemes become FeIV. In the absence of preMADH the hemes autoreduce to ferric in a multistep process involving multiple electron and proton transfers. Binding of preMADH in the absence of catalysis alters the mechanism of autoreduction of the ferryl heme. Thus, substrate binding alters the environment in the distal heme pocket of the high-spin heme over very long distance

Properties Of The High-Spin Heme Of Maug Are Altered By Binding Of Premadh At The Protein Surface 40 Å Away

The diheme enzyme MauG catalyzes oxidative post-translational modifications of a protein substrate, precursor protein of methylamine dehydrogenase (preMADH), that binds to the surface of MauG. The high-spin heme iron of MauG is located 40 Å from preMADH. The ferric heme is an equilibrium of five- and six-coordinate states. PreMADH binding increases the proportion of five-coordinate heme three-fold. On reaction of MauG with H2O2 both hemes become FeIV. In the absence of preMADH the hemes autoreduce to ferric in a multistep process involving multiple electron and proton transfers. Binding of preMADH in the absence of catalysis alters the mechanism of autoreduction of the ferryl heme. Thus, substrate binding alters the environment in the distal heme pocket of the high-spin heme over very long distance

A T67A Mutation In The Proximal Pocket Of The High-Spin Heme Of Maug Stabilizes Formation Of A Mixed-Valent Fe\u3csup\u3eIi\u3c/sup\u3e/Fe\u3csup\u3eIii\u3c/sup\u3e State And Enhances Charge Resonance Stabilization Of The Bis-Fe\u3csup\u3eIv\u3c/sup\u3e State

The diheme enzyme MauG catalyzes a six-electron oxidation required for posttranslational modification of a precursor of methylamine dehydrogenase (preMADH) to complete the biosynthesis of its protein-derived tryptophan tryptophylquinone (TTQ) cofactor. One heme is low-spin with ligands provided by His205 and Tyr294, and the other is high-spin with a ligand provided by His35. The side chain methyl groups of Thr67 and Leu70 are positioned at a distance of 3.4 Å on either side of His35, maintaining a hydrophobic environment in the proximal pocket of the high-spin heme and restricting the movement of this ligand. Mutation of Thr67 to Ala in the proximal pocket of the high-spin heme prevented reduction of the low-spin heme by dithionite, yielding a mixed-valent state. The mutation also enhanced the stabilization of the charge-resonance-transition of the high-valent bis-FeIV state that is generated by addition of H2O2. The rates of electron transfer from TTQ biosynthetic intermediates to the high-valent form of T67A MauG were similar to that of wild-type MauG. These results are compared to those previously reported for mutation of residues in the distal pocket of the high-spin heme that also affected the redox properties and charge resonance transition stabilization of the high-valent state of the hemes. However, given the position of residue 67, the structure of the variant protein and the physical nature of the T67A mutation, the basis for the effects of the T67A mutation must be different from those of the mutations of the residues in the distal heme pocket

Carboxyl Group Of Glu113 Is Required For Stabilization Of The Diferrous And Bis-Fe\u3csup\u3eIv\u3c/sup\u3e States Of Maug

The diheme enzyme MauG catalyzes a six-electron oxidation required for post-translational modification of a precursor of methylamine dehydrogenase (preMADH) to complete the biosynthesis of its protein-derived tryptophan tryptophylquinone (TTQ) cofactor. Crystallographic studies have implicated Glu113 in the formation of the bis-FeIV state of MauG, in which one heme is FeIVî - O and the other is FeIV with His-Tyr axial ligation. An E113Q mutation had no effect on the structure of MauG but significantly altered its redox properties. E113Q MauG could not be converted to the diferrous state by reduction with dithionite but was only reduced to a mixed valence FeII/FeIII state, which is never observed in wild-type (WT) MauG. Addition of H2O2 to E113Q MauG generated a high valence state that formed more slowly and was less stable than the bis-FeIV state of WT MauG. E113Q MauG exhibited no detectable TTQ biosynthesis activity in a steady-state assay with preMADH as the substrate. It did catalyze the steady-state oxidation of quinol MADH to the quinone, but 1000-fold less efficiently than WT MauG. Addition of H 2O2 to a crystal of the E113Q MauG-preMADH complex resulted in partial synthesis of TTQ. Extended exposure of these crystals to H2O2 resulted in hydroxylation of Pro107 in the distal pocket of the high-spin heme. It is concluded that the loss of the carboxylic group of Glu113 disrupts the redox cooperativity between hemes that allows rapid formation of the diferrous state and alters the distribution of high-valence species that participate in charge-resonance stabilization of the bis-Fe IV redox state. © 2013 American Chemical Society

Carboxyl Group of Glu113 Is Required for Stabilization of the Diferrous and Bis-Fe^IV States of MauG

The diheme enzyme MauG catalyzes a six-electron oxidation required for post-translational modification of a precursor of methylamine dehydrogenase (preMADH) to complete the biosynthesis of its protein-derived tryptophan tryptophylquinone (TTQ) cofactor. Crystallographic studies have implicated Glu113 in the formation of the bis-Fe^IV state of MauG, in which one heme is Fe^IVO and the other is Fe^IV with His-Tyr axial ligation. An E113Q mutation had no effect on the structure of MauG but significantly altered its redox properties. E113Q MauG could not be converted to the diferrous state by reduction with dithionite but was only reduced to a mixed valence Fe^II/Fe^III state, which is never observed in wild-type (WT) MauG. Addition of H₂O₂ to E113Q MauG generated a high valence state that formed more slowly and was less stable than the bis-Fe^IV state of WT MauG. E113Q MauG exhibited no detectable TTQ biosynthesis activity in a steady-state assay with preMADH as the substrate. It did catalyze the steady-state oxidation of quinol MADH to the quinone, but 1000-fold less efficiently than WT MauG. Addition of H₂O₂ to a crystal of the E113Q MauG-preMADH complex resulted in partial synthesis of TTQ. Extended exposure of these crystals to H₂O₂ resulted in hydroxylation of Pro107 in the distal pocket of the high-spin heme. It is concluded that the loss of the carboxylic group of Glu113 disrupts the redox cooperativity between hemes that allows rapid formation of the diferrous state and alters the distribution of high-valence species that participate in charge-resonance stabilization of the bis-Fe^IV redox state

FAPbI\u3csub\u3e3\u3c/sub\u3e Perovskite Films Prepared by Solvent Self-Volatilization for Photovoltaic Applications

Developing a simple method to synthesize the perovskite layer without the antisolvent technique can facilitate the industrial production of perovskite solar cells (PSCs). Limited progress has been made for the antisolvent-free method on formamidinium lead triiodide perovskite layers because of the phase stability issue. Here, we use N-methyl pyrrolidone (NMP) as an additive to inhibit the nonperovskite phase of FAPbI3 to fabricate the formamidinium iodide (FAI)–PbI2–NMP intermediate phase via the self-volatilization of volatile solvent 2-methoxyethanol instead of the traditional antisolvent method. The high-quality pure α phase of FAPbI3 films is obtained by phase transition via annealing. The photovoltaic properties of the perovskite films affected by different NMP amounts are studied. The corresponding PSCs show a PCE of 20.1% compared to 15.6% for the PSCs fabricated with the classical antisolvent technique. The unencapsulated devices exhibit ∼75% efficiency of their initial PCE values after 35 days of storage. This method can be used in the scalable production of PSCs because of high reproducibility and easy operation