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University of Groningen Discovery of a Eugenol Oxidase From University of Groningen Discovery of a eugenol oxidase from Rhodococcus sp strain RHA1 Jin, J.F.; Mazon, H.; van den Heuvel, R.H.H.; Janssen, D.B.; Fraaije, M.W. Published in: Febs Journal DOI: 10.1111/j.1742-4658.2007.05767.x IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2007 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Jin, J. F., Mazon, H., van den Heuvel, R. H. H., Janssen, D. B., & Fraaije, M. W. (2007). Discovery of a eugenol oxidase from Rhodococcus sp strain RHA1. Febs Journal, 274(9), 2311 - 2321. https://doi.org/10.1111/j.1742-4658.2007.05767.x Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 23-09-2021 Discovery of a eugenol oxidase from Rhodococcus sp. strain RHA1 Jianfeng Jin1, Hortense Mazon2, Robert H. H. van den Heuvel2, Dick B. Janssen1 and Marco W. Fraaije1 1 Laboratory of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, the Netherlands 2 Department of Biomolecular Mass Spectrometry, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, the Netherlands Keywords A gene encoding a eugenol oxidase was identified in the genome from Rho- covalent flavinylation; eugenol; flavin; dococcus sp. strain RHA1. The bacterial FAD-containing oxidase shares oxidase; Rhodococcus 45% amino acid sequence identity with vanillyl alcohol oxidase from the fungus Penicillium simplicissimum. Eugenol oxidase could be expressed at Correspondence M. W. Fraaije, Laboratory of Biochemistry, high levels in Escherichia coli, which allowed purification of 160 mg of Groningen Biomolecular Sciences and eugenol oxidase from 1 L of culture. Gel permeation experiments and Biotechnology Institute, University of macromolecular MS revealed that the enzyme forms homodimers. Eugenol Groningen, Nijenborgh 4, 9747 AG oxidase is partly expressed in the apo form, but can be fully flavinylated by Groningen, The Netherlands the addition of FAD. Cofactor incorporation involves the formation of a Fax: +31 50 3634165 covalent protein–FAD linkage, which is formed autocatalytically. Modeling Tel: +31 50 3634345 using the vanillyl alcohol oxidase structure indicates that the FAD cofactor E-mail: [email protected] is tethered to His390 in eugenol oxidase. The model also provides a struc- (Received 8 January 2007, revised 21 tural explanation for the observation that eugenol oxidase is dimeric February 2007, accepted 2 March 2007) whereas vanillyl alcohol oxidase is octameric. The bacterial oxidase effi- )1 ciently oxidizes eugenol into coniferyl alcohol (KM ¼ 1.0 lm, kcat ¼ 3.1 s ). doi:10.1111/j.1742-4658.2007.05767.x Vanillyl alcohol and 5-indanol are also readily accepted as substrates, whereas other phenolic compounds (vanillylamine, 4-ethylguaiacol) are converted with relatively poor catalytic efficiencies. The catalytic effi- ciencies with the identified substrates are strikingly different when com- pared with vanillyl alcohol oxidase. The ability to efficiently convert eugenol may facilitate biotechnological valorization of this natural aromatic compound. The flavoenzyme vanillyl alcohol oxidase (VAO, event [5,6]. As well as oxidizing alcohols, the fungal EC 1.1.3.38) from Penicillium simplicissimum is active enzyme is also able to perform amine oxidations, enan- on a range of phenolic compounds [1,2]. It contains a tioselective hydroxylations, and oxidative ether-clea- covalently linked FAD cofactor, and the holoprotein vage reactions [7,8]. Several substrates can serve as forms stable octamers. VAO was the first histidyl- vanillin precursors (e.g. vanillyl alcohol, vanillyl amine FAD-containing flavoprotein for which the crystal and creosol) [9,10]. Recently, VAO has been used in structure was determined [3], and serves as a prototype metabolic engineering experiments with the aim of cre- for a specific flavoprotein family [4]. Mutagenesis stud- ating a bacterial whole cell biocatalyst that is able to ies have shown that the covalent flavin–protein bond is form vanillin from eugenol [11,12]. However, VAO is crucial for efficient catalysis, and that covalent flaviny- poorly expressed in bacteria, resulting in a relatively lation of the apoprotein proceeds via an autocatalytic low intracellular VAO activity [12] and low yields of Abbreviations EUGO, eugenol oxidase; PCMH, p-cresol methylhydroxylase (EC 1.17.99.1); VAO, vanillyl alcohol oxidase (EC 1.1.3.38). FEBS Journal 274 (2007) 2311–2321 ª 2007 The Authors Journal compilation ª 2007 FEBS 2311 Discovery of a eugenol oxidase J. Jin et al. purified VAO when Escherichia coli is used as the ture, about 160 mg of yellow-colored recombinant expression host [13]. EUGO was purified. The purified enzyme migrated as In a quest for a bacterial VAO, we have searched a single band on SDS ⁄ PAGE, corresponding to a mass the sequenced bacterial genomes for VAO homologs. of about 58 kDa (Fig. 2, lane 4a). This agrees well Such a search is complicated by the fact that bacterial with the predicted mass of 58 681 Da (excluding the hydroxylases, p-cresol methylhydroxylase (PCMH) [14] FAD cofactor). A fluorescent band was visible when and eugenol hydroxylase [15,16], have been reported the gel was soaked in 5% acetic acid and placed under that show sequence identity with VAO. PCMH and UV light. This indicates that a flavin cofactor is cova- eugenol hydroxylase display similar substrate specifici- lently linked to the enzyme. Unfolding and precipita- ties when compared with VAO [16–18]. For VAO and tion by trichloroacetic acid resulted in formation of a PCMH, several crystal structures have been elucidated yellow protein aggregate, which confirms that the fla- showing that the respective active sites are remarkably vin cofactor is covalently bound to the protein. conserved [3,18]. This is in line with the overlapping The purified enzyme showed absorption maxima in substrate specificities. However, a major difference the visible region at 365 nm and 441 nm, and shoul- between VAO and the bacterial hydroxylases is the ders at 313 nm, 394 nm, and 461 nm (Fig. 3). Upon ability of VAO to use molecular oxygen as electron unfolding of the enzyme in 0.5% SDS, the absorption acceptor. Instead, the bacterial hydroxylases employ maximum at 441 nm slightly decreased in intensity and cytochrome domains to relay the electrons towards shifted to 450 nm. If it is assumed that the molar azurin as electron acceptor. Another difference absorption coefficient of the unfolded enzyme is com- between VAO and the bacterial hydroxylases is the parable to that of 8a-substituted FAD [20], a value of mode of binding of the FAD cofactor. In VAO, FAD 14.2 mm)1Æcm)1 can be calculated for the molar extinc- is covalently bound to a histidine, whereas the bacter- tion coefficient of the native enzyme. These spectral ial counterparts contain a tyrosyl-linked FAD cofactor characteristics are very similar to those of VAO [1], [3,19]. It has been shown that in PCMH, the electron indicating that the FAD cofactor is in a similar micro- transfer from the reduced flavin cofactor to the cyto- environment and histidyl-linked. The presence of a chrome subunit is facilitated by the covalent FAD–tyr- histidyl-linked FAD cofactor agrees with the model osyl linkage. For VAO, it has been demonstrated that that could be prepared of EUGO. The structural the covalent FAD–histidyl linkage induces a relatively model shows that His390 is in a similar position to the high redox potential, allowing the enzyme to use FAD-linking His422 in VAO (Fig. 4). molecular oxygen as electron acceptor [5]. It has been observed that most flavoprotein oxidases By surveying the available sequenced genomes, a can form a stable covalent adduct with sulfite. How- number of VAO homologs can be found: 25 bacterial ever, the purified enzyme did not form such a covalent and fungal homologs with sequence identity of sulfite–flavin adduct, as no spectral changes occurred > 30%. A putative VAO from Rhodococcus sp. strain upon incubation with 10 mm sulfite. A similar reluct- RHA1 was found to display sequence identity with ance to react with sulfite has been observed with a VAO (45%) (40% with PCMH). Sequence alignment selected number of flavoprotein oxidases, including with its characterized homologs revealed that it con- VAO from P. simplicissimum [1]. tains a histidine residue (His390) at the equivalent position of the FAD-binding histidine in VAO Catalytic properties of EUGO (Fig. 1). This suggested that this enzyme might repre- sent a bacterial VAO. In this article, we describe the Like VAO from P. simplicissimum, EUGO exhibits a production, purification and characterization of this wide substrate spectrum. Table 1 shows the steady- novel oxidase from Rhodococcus sp. strain RHA1. The state kinetic parameters of the bacterial oxidase with bacterial oxidase was found to be most active with all identified phenolic substrates. It is evident that eugenol, and hence has been named eugenol oxidase eugenol is the best substrate, and therefore we have (EUGO). named the enzyme eugenol oxidase. Aerobic incuba- tion of eugenol with EUGO led to full conversion into coniferyl alcohol, as judged by formation of a typical Results UV–visible spectrum indicative for this aromatic com- pound (Fig.
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