A Model Compound of the Novel Cofactor Tryptophan Tryptophylquinone of Bacterial Methylamine Dehydrogenases. Synthesis and Physicochemical Properties

Itoh, Shinobu; Ogino, Masao; Haranou, Shigenobu; Terasaka, Tadashi; Ando, Takehiro; Komatsu, Mitsuo; Ohshiro, Yoshiki; Fukuzumi, Shunichi; Kano, Kenji

doi:10.1021/ja00110a004

Cited by 68 publications

(88 citation statements)

References 4 publications

(6 reference statements)

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“…disproportionates more rapidly) in AADH than in MADH. The conclusion that the semiquinone in MADH and AADH is unprotonated is consistent with results obtained with the TTQ model compound (16). This conclusion is also reasonable because semiquinones typically exhibit pK a values Ͻ6.…”

Section: Discussionsupporting

confidence: 88%

“…The reduced cofactor is TTQH Ϫ . A pK a Ͼ 8.5 is expected for organic O-quinols and consistent with the pK a for the TTQ model compound of 10.1 (16). In the model compound, however, both hydroxyls are protonated.…”

Section: Resultssupporting

confidence: 75%

“…A similar value was reported for MADH from bacterium W3A1 (15). Recently, the redox properties of a TTQ model compound were reported (16). It exhibited an E m value similar to that of MADH at pH 7.5.…”

supporting

confidence: 82%

“…An important aim of this study is to determine how the protein influences the redox properties of the TTQ prosthetic group and whether this influences the catalytic properties of the protein-bound quinone in the quinoprotein. Itoh et al (16) performed a detailed analysis of the redox properties of a model compound of TTQ in which methyl groups are present at the positions where the rings are covalently attached to the protein. Differences in the redox properties of the protein-bound TTQ in MADH and the model compound may be interpreted in the context of the known crystal structure of MADH (17,18).…”

Section: Discussionmentioning

confidence: 99%

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Redox Properties of Tryptophan Tryptophylquinone Enzymes

Zhu

Davidson

1998

Journal of Biological Chemistry

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The pH dependence of the redox potentials for the oxidized/reduced couples of methylamine dehydrogenase (MADH) and aromatic amine dehydrogenase (AADH) were determined. For each enzyme, a change of ؊30 mV/pH unit was observed, indicating that the two-electron transfer is linked to the transfer of a single proton. This result differs from what was obtained from redox studies of a tryptophan tryptophylquinone (TTQ) model compound for which the two-electron couple is linked to the transfer of two protons. This result also distinguishes the redox properties of the enzyme-bound TTQ from those of the membrane-bound quinone components of respiratory and photosynthetic electron transfer chains that transfer two protons per two electrons. This difference is attributed to the accessibility of TTQ to solvent in the enzymes. One of the quinol hydroxyls is shielded from solvent and thus is not protonated. The unusual property of TTQ enzymes of stabilizing the anionic form of the reduced quinol is important for the reaction mechanism of MADH because it allows stabilization of physiologically important reaction intermediates. Examination of the extent to which disproportionation of the MADH and AADH semiquinones occurred as a function of pH revealed that the equilibrium concentration of semiquinone increased with pH. This indicates that the proton transfer is linked to the semiquinone/quinol couple. Therefore, the quinol is singly protonated, and the semiquinone is unprotonated and anionic. It was also shown that the oxidation-reduction midpoint potential for AADH is 20 mV less positive than that of MADH over the range of pH values that was studied and that the TTQ semiquinone of AADH was less stable than that of MADH. This may be explained by differences in the active site environments of the two enzymes, which modulate their respective redox properties.Redox reactions involving proteins are ubiquitous processes that are fundamental to respiration, photosynthesis, and reactions of intermediary metabolism. Enzyme-bound quinones and flavins are important cofactors of oxidoreductases that function in biological catalysis and electron transfer. These prosthetic groups, as well as membrane-bound components of respiratory electron transfer chains, are particularly important because they are able to couple the two-electron oxidation of substrates to single electron carriers during metabolism and respiration.Methylamine dehydrogenase (MADH; reviewed in Ref. 1) 1 catalyzes the oxidation of methylamine in the periplasm of many methylotrophic and autotrophic bacteria to form ammonia and formaldehyde concomitant with the two-electron reduction of its redox cofactor (Reaction 1). MADH isan H 2 L 2 heterotetramer with subunit molecular masses of 47 and 15 kDa. The tryptophan tryptophylquinone (TTQ; Fig. 1) (2) prosthetic group, which is located on each small subunit, is derived from two tryptophan side chains that are covalently cross-linked and contain an orthoquinone function through a post-translational modification. In autotrophic bacte...

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Section: Discussionsupporting

confidence: 88%

Section: Resultssupporting

confidence: 75%

supporting

confidence: 82%

Section: Discussionmentioning

confidence: 99%

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Redox Properties of Tryptophan Tryptophylquinone Enzymes

Zhu

Davidson

1998

Journal of Biological Chemistry

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“…Since the mixing of mCPBA and tryptophan does not produce the modified tryptophan, a ferryl porphyrin radical cation generated in the reaction of F43W/H64L Mb with mCPBA is presumably a catalytic species to form 6-hydroxytryptophan either directly or via the epoxidation followed by hydrolysis (Scheme 3). Previous studies using Fremy's salt as the oxidant indicate that 6-hydroxy-3-methylindole is readily oxidized to yield 3-methylindole 2,6-and 6,7-dione, and 6,7-dione is reported to be a minor product due to its instability (yield of 3-methylindole 2,6-dione ϭ 63%, 6,7-dione ϭ 7%) (22). We expect that 6-hydroxytryptophan could further be oxidized with mCPBA (Scheme 3A) or compound I (Scheme 3B) by overall four electron oxidation to produce the 2,6-dihydro-2,6-dioxoindole substructure.…”

Section: H Nmr Chemical Shifts (␦ In Ppm) Of Trp-43 Of the Intact Wdrmentioning

confidence: 99%

Oxidative Modification of Tryptophan 43 in the Heme Vicinity of the F43W/H64L Myoglobin Mutant

Hara¹,

Ueno²,

Ozaki³

et al. 2001

Journal of Biological Chemistry

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The F43W/H64L myoglobin mutant was previously constructed to investigate the effects of electron-rich tryptophan residue in the heme vicinity on the catalysis, where we found that Trp-43 in the mutant was oxidatively modified in the reaction with m-chloroperbenzoic acid (mCPBA). To identify the exact structure of the modified tryptophan in this study, the mCPBAtreated F43W/H64L mutant has been digested stepwise with Lys-C achromobacter and trypsin to isolate two oxidation products by preparative fast protein liquid chromatography. The close examinations of the 1 H NMR spectra of peptide fragments reveal that two forms of the modified tryptophan must have 2,6-disubstituted indole substructures. The 13 C NMR analysis suggests that one of the modified tryptophan bears a unique hydroxyl group in stead of the NH 2 group at the amino-terminal. The results together with mass spectrometry (MS)/MS analysis (30 Da increase in mass of Trp-43) indicate that oxidation products of Trp-43 are 2,6-dihydro-2,6-dioxoindole and 2,6-dihydro-2-imino-6-oxoindole derivatives. Our finding is the first example of the oxidation of aromatic carbons by the myoglobin mutant system. Myoglobin (Mb), 1 a carrier of molecular oxygen, can perform oxidation reactions in the presence of hydrogen peroxide (H 2 O 2 ), although the activity is not as great as that of peroxidase (1-3). The accumulated biochemical and biophysical data allow us to utilize Mb as a heme enzyme model system, and various myoglobin mutants have been constructed to elucidate structure-function relationship on the activation of peroxides (3-5). For example, F43H/H64L Mb, one of the distal histidine relocation mutants, exhibits the enhanced reactivity with H 2 O 2 and the longer lifetime of an active intermediate, a ferryl porphyrin radical cation (OϭFe IV porphyrin ⅐ ϩ ) (6). Therefore as the results, the F43H/H64L mutant is able to catalyze the sulfoxidation and epoxidation reaction at the rate comparable with the values of peroxidases.On the other hand, cytochromes P-450 (P-450) catalyze the hydroxylation of a wide variety of substrates, including hydrocarbons and polycyclic aromatic molecules (7,8). The variance in reactivity of Mb and P-450 could arise from differences in the active site structure and the arrangement of functional amino acid residues. The crystal structure of P-450cam with d-camphor reveals that the substrate is tightly bound in the hydrophobic heme pocket through hydrogen bonding interaction with the hydroxyl group of Tyr-96 and the carbonyl oxygen of dcamphor (Fig. 1A) (9). The distance between the heme iron and C5 of d-camphor, the hydroxylation site, is 4.2 Å. On the contrary, the active site of myoglobin is exposed to the exterior and does not provide any specific interactions for accommodating a foreign substrate with high affinity (10). Therefore, it will be difficult for a ferryl porphyrin radical cation of Mb to hydroxylate a substrate molecule, which is not bound in an appropriate position nearby the heme. We hypothesize that a ferryl oxygen atom...

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Quinone Cofactors

Lang

Klinman

2013

Encyclopedia of Life Sciences

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Quinone cofactors are used by several classes of enzymes, which catalyse the oxidation of biogenic amines and alcohols, to help catalyse these reactions. Before 1990 only one cofactor, the peptide‐derived pyrroloquinoline quinone had been identified. During 1990–2001, however, four new quinone prosthetic groups derived from naturally occurring amino acids were discovered. The first protein‐derived, nondissociable cofactor identified was 2,4,5‐trihydroxyphenylalanine quinone, designated topaquinone (TPQ) in copper amine oxidases . The discovery of TPQ led to the identification of a series of new quinone cofactors, including lysine tyrosylquinone (LTQ) in lysyl oxidase, cysteine tryptophylquinone (CTQ) in quinohaemoprotein amine dehydrogenase and tryptophan tryptophylquinone (TTQ) in bacterial methylamine dehydrogenase . These cofactors contribute electrophillic capabilities (and stabilise free radical intermediates) that naturally occurring, unmodified amino acid side chains are unable to provide. Key Concepts: Quinone cofactors are a class of cofactors used by many enzymes to catalyse the oxidation of amines and alcohols. Five quinone cofactors have been characterised: PQQ, TPQ, LTQ, TTQ and CTQ. PQQ is a peptide‐derived cofactor that involves the expression of six genes located within an operon. TPQ is derived from a precursor tyrosine and requires only Cu 2+ and O 2 for biogenesis. LTQ is formed by the cross‐linking of a tyrosine residue and a lysine residue, also requiring only Cu 2+ and O 2 . TTQ is formed by the cross‐linking of two tryprophan resides, with MauG completing biogenesis. CTQ, the most recently discovered quinone cofactor, is formed by the cross‐linking of a cysteine reside and a tryptophan residue.

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A Model Compound of the Novel Cofactor Tryptophan Tryptophylquinone of Bacterial Methylamine Dehydrogenases. Synthesis and Physicochemical Properties

Cited by 68 publications

References 4 publications

Redox Properties of Tryptophan Tryptophylquinone Enzymes

Redox Properties of Tryptophan Tryptophylquinone Enzymes

Oxidative Modification of Tryptophan 43 in the Heme Vicinity of the F43W/H64L Myoglobin Mutant

Quinone Cofactors

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