Topa quinone

Klinman JP. 2003. The multi-functional topa-quinone copper amine oxidases. Biochim Biophys Acta 1647 131. 

M. Mure, S.A. Mills, J.P. Klinman, Catalytic mechanism of the topa quinone containing copper amine oxidases. Biochemistry 41 (2002) 9269-9278. 

S. Hirota, T. Iwamoto, S. Kishishita, T. Okajima, O. Yamauchi, K. Tanizawa, Spectroscopic observation of intermediates formed during the oxidative half-reaction of copper/topa quinone-containing phenylethylamine oxidase, Biochemistry 40 (2001) 15789-15796. 

Turowski P. N. McGuirl M. A. Dooley D. M. Intramolecular electron transfer rate between active-site copper and topa quinone in pea seedling amine oxidase. J. Biol. Chem. 1993, 268, 17680-17682. 

Matsuzaki, R., Fukui, T., Sato, H., Ozaki, Y., and Tanizawa, K., 1994, Generation of the TOPA quinone cofactor in bacterial monoamine oxidase by cupric ion-dependent autooxidation of a specific tyrosyl residue, EEBS Lett. 351 360n364. 

Moenne-Loccoz, P., Nakamura, N., Steinebach, V., Duine, J. A., Mure, M., Klinman, J. P., and Sanders-Loehr, J., 1995, Characterisation of the TOPA quinone cofactor in amine oxidase from Escherichia coli by resonance Raman spectroscopy, 1995 Biochemistry 34 7020n7026. 

Mu, D., Janes, S. M., Smith, A. J., Brown, D. E., Dooley, D. M., and Klinman, J. P., 1992, Tyrosine codon corresponds to TOPA quinone at the active site of copper amine oxidases, J. Biol. Chem. 267 7979n7982. 

Ruggiero, C. E., and Dooley, D. M., 1999, Stoichiometry of the TOPA quinone biogenesis reaction in copper amine oxidases, Biochemistry 38 2892n2898. 

Figure 6 Post-translationally generated cofactors provide functional groups to allow catalysis. The mechanisms of TOPA quinone in amine oxidases, MiO in deaminases, and pyruvamide in decarboxyiases are shown.

Structure of the active center. The active centers of this dimeric enzyme are so well embedded into its protein structure that they are inaccessible to the solvent. The two centers are situated approximately 30 A apart from each other but connected by /3-strands. The active center consists of a type 2 copper center and a cofactor. Sequence comparisons have established that the residues His 8, His 246, and His 357 coordinate the copper ions in both yeast and plants (e.g., lentil seeds) [120,122]. The participating cofactor is typical for amine oxidases, diamine oxidases, and lysyl oxidases but has not yet been found in any other protein - 2,4,5-trihydroxy-phenylalanine quinone [123, 124] (also known as TOPA-quinone, TPQ or 6-hydroxy-DOPA quinone), an internal cofactor which is created by post-translational modification of the tyrosine in position 387 [120]. The consensus sequence of the amino acids neighboring the TOPA cofactor are conserved in all known amine oxidases - Asn-TOPA-Asp/Glu [113,120, 123,125-127]. The positions of the histidine ligands relative to TOPA quinone are conserved in all known amine oxidases as well. The chain lengths of the amine oxidase monomers vary according to the organism of origin 692 residues in yeast [128], 762 in bovine serum amine oxidase [128,129] and 569 in the enzyme from lentil seeds [120,130]. 

Fig. 17. Synthesis of the TOPA quinone cofactor in amine oxidases. From Cai and Klinman 1994 [113] with permission...

Fig. 18. Catalytic cycle of the amine oxidases. Only TOPA quinone is required for catalysis copper functions solely as a cofactor in its synthesis. From [28] with permission...

The postulated catalytic mechanism of amine oxidases starts from the qui-none form of the cofactor (Fig. 17). The distal oxygen atom is replaced by an amino group in a transamination reaction. The amine is then re-oxidized by molecular oxygen to the original quinone. The copper ion is not involved directly in catalysis but is only a cofactor in the synthesis of TOPA quinone (Fig. 18). 

Galactose oxidase (EC 1.1.3.9) differs significantly from the other non-blue oxidases. The enzyme (from the fungus Dactylium dendroides) consists of a single peptide chain of 639 amino acids [152] and has a molecular mass of 68 kD [30]. The active center contains a single type 2 copper center. It has neither additional, dissociable prosthetic groups nor TOPA quinone, the typical cofactor of the other non-blue oxidases [153]. 

Galactose oxidase, as well as the other non-blue oxidases, avoids the necessity of an external cofactor by creating an internal cofactor via modification of a residue of its own peptide chain. The amino acid residue which is modified in all cases is a tyrosine. While the amine oxidases produce TOPA quinone, galactose oxidase forms a thioether bond between the tyrosine and a cysteine residue. This modified tyrosine is the site which carries the free radical. 

COPPER/TOPA QUINONE-CONTAINING AMINE OXIDASES - RECENT RESEARCH DEVELOPMENTS... 

Fig. (I). Topa quinone as a part of the cofactor consensus amino acid sequence in the active site of copper amine oxidases [4],...

The results were further confirmed by resonance Raman spectrometry on comparing the spectra of phenylhydrazone and p-nitrophenylhydrazone of bovine plasma amine oxidase with the derivatized pentapeptides of the active site and the model compound. All these spectra showed great similarity in position (wavenumber) and spectral band intensity, while the spectrum of a PQQ model compound differed markedly [45]. Similar experiments confirmed the presence of topa quinone in porcine kidney, pea seedling and Arthrobacter PI amine oxidases. Moreover, the experimental data obtained for intact enzymes excluded the possibility of an artificial topa quinone formation during the proteolysis and peptide isolation [45]. 

Later, the presence of topa quinone was accordingly confirmed in the amine oxidases from porcine serum and kidney and pea seedling by resonance Raman spectrometry of active-site labeled peptides [48]. Comparison of amino acid sequences of these peptides with the sequences of those from bovine plasma and H. polymorpha amine oxidases demonstrated the presence of a consensus sequence Asp-TPQ-Asp/Glu as shown in Fig. (1). Using the pH-dependent shift of the absorption maximum of the enzyme p-nitrophenylhydrazone, which is considered to be a reliable indirect proof, the presence of topa quinone was also shown... 

Recently, the cofactor peptides have also been isolated from semicarbazide-sensitive amine oxidases purified from bovine and porcine aortas [52], sequenced and confirmed to contain the topa quinone. The same topa quinone consensus sequence was also found in the primary structures of amine oxidases from human kidney [53], human retina [54] and rat colon [55], so called amiloride-binding proteins , and amine oxidase from human placenta [56] that shows 81% identity with bovine plasma amine oxidase [57], bovine lung amine oxidase [58], and amine oxidases from pea and lentil seedlings [59,60], chick pea seedlings [61], and Arabidopsis thaliana [62] obtained by the molecular cloning of respective DNAs. 

In the amine oxidase from Escherichia coli, the topa quinone was confirmed by a detailed analysis of the cofactor dipeptide X-Asp [67] and the resonance Raman spectrometry of the enzyme and its derivatives[68,69]. The primary structure of the enzyme also contains the cofactor consensus sequence [70]. More bacterial genes were shown to encode proteins containing the topa quinone consensus sequence, such as amine oxidase from Klebsiella aerogenes [71], phenethylamine oxidase and histamine oxidase from Arthrobacter globiformis [72,73], and methylamine oxidase from Arthrobacter strain PI [74]. Amino acid sequences around the position of the cofactor for selected amine oxidases from various sources are given in Table 1. 

Table 1. Alignment of amino acid sequences of several copper amine oxidase around the position of topa quinone. The sequences were obtained by translation the corresponding cDNAs except for the enzymes from porcine kidney and porcine serum and the benzylamine oxidase from Hansenula polymorpha where they were determined by automated Edman degradation of peptides. Homologous consensus sequence around the cofactor is underlined, the tyrosyl precursor of topa quinone is shown as y.

Fig. (3). Mechanism of the substrate oxidation by copper amine oxidases [29]. The scheme shows the roles of copper, topa quinone cofactor and proton abstracting base (Asp) in the catalytic cycle. The oxidized enzyme (a) reacts with an amine substrate giving a Schiff base formation at C-5 of the TPQ (b-c), followed by proton abstraction (d). After hydrolysis and release of the aldehyde, an aminoresorcinol species is formed (e), and the reduced cofactor is reoxidized by molecular oxygen via Cu(I)-semiquinone intermediate (/).

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