University of Groningen Flavoprotein oxidases Dijkman, Willem P.; de Gonzalo, Gonzalo; Mattevi, Andrea; Fraaije, Marco W. Published in: Applied Microbiology and Biotechnology DOI: 10.1007/s00253-013-4925-7 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: 2013 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Dijkman, W. P., de Gonzalo, G., Mattevi, A., & Fraaije, M. W. (2013). Flavoprotein oxidases: classification and applications. Applied Microbiology and Biotechnology, 97(12), 5177-5188. https://doi.org/10.1007/s00253-013-4925-7 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: 28-09-2021 Appl Microbiol Biotechnol (2013) 97:5177–5188 DOI 10.1007/s00253-013-4925-7 MINI-REVIEW Flavoprotein oxidases: classification and applications Willem P. Dijkman & Gonzalo de Gonzalo & Andrea Mattevi & Marco W. Fraaije Received: 13 February 2013 /Revised: 10 April 2013 /Accepted: 11 April 2013 /Published online: 3 May 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract This review provides an overview of oxidases reactions. Known oxidative enzyme classes are the oxi- that utilise a flavin cofactor for catalysis. This class of dases, oxygenases and dehydrogenases. Oxygenases require oxidative flavoenzymes has shown to harbour a large num- reducing equivalents [e.g. NAD(P)H] and molecular oxy- ber of biotechnologically interesting enzymes. Applications gen for activity, while dehydrogenases utilise organic co- range from their use as biocatalysts for the synthesis of enzymes (for example pyrroloquinoline quinone, quinones pharmaceutical compounds to the integration in biosensors. or NAD+) as electron acceptors. The coenzyme dependence Through the recent developments in genome sequencing, of these enzymes can compromise cost-effective biotechno- the number of newly discovered oxidases is steadily grow- logical applications. Instead of (often expensive) coen- ing. Recent progress in the field of flavoprotein oxidase zymes, oxidases merely require molecular oxygen as discovery and the obtained biochemical knowledge on these oxidant (electron acceptor) for catalysis. This feature makes enzymes are reviewed. Except for a structure-based classi- them valuable enzymes for industrial applications that fication of known flavoprotein oxidases, also their potential range from oxidase-based biosensors to their application in recent biotechnological applications is discussed. as biocatalysts in the synthesis of valuable chemicals. For an organism, however, oxidases are much less favourable. Keywords Flavoproteins . Oxidases . Biocatalysis . By the direct reduction of molecular oxygen, electrons are Biosensors . Flavin . Oxygen lost and cannot be used in subsequent metabolic events, as in the case of dehydrogenases. Another physiological rele- vant issue concerning oxidases is their inherent reactivity Introduction to produce reduced dioxygen species. While some oxidases are capable to reduce dioxygen to harmless water, most Selective oxidations are often key in synthetic routes to- oxidases generate instead hydrogen peroxide as by-product, wards valuable chemicals. Chemical oxidation methods typ- and even in some cases, the even more toxic superoxide − ically require harsh conditions and polluting reagents and O2 is formed. The features above provide logic for why often suffer from poor chemoselectivity and enantioselectivity. oxidases are relatively rare enzymes. Nature, on the other hand, has come up with a versatile set of Most oxidases rely on a tightly bound cofactor for their enzymes performing a wide variety of selective oxidation activity, and only a few examples of cofactor independent oxidases have been described (Fetzner and Steiner 2010). W. P. Dijkman : G. de Gonzalo : M. W. Fraaije (*) This is due to the fact that amino acids are very poor in Molecular Enzymology Group, Groningen Biomolecular Sciences mediating redox reactions. To equip enzymes with oxidising and Biotechnology Institute, University of Groningen, power, nature has evolved several different redox cofactors. Nijenborgh 4, For oxidases, there is a bias towards two types of cofactors 9747 AG Groningen, The Netherlands e-mail: [email protected] resulting in two main oxidase families. One family utilises URL: www.rug.nl/staff/m.w.fraaije/research copper in mono- and trinuclear centers or a copper atom combined with a quinone cofactor. The reader is refereed to A. Mattevi many reviews on this topic (Guengerich 2012; Ridge et al. Department of Biology and Biotechnology, University of Pavia, Via Ferrata 1, 2008). This review will focus on the other major oxidase 27100 Pavia, Italy family: the flavin-containing oxidases. 5178 Appl Microbiol Biotechnol (2013) 97:5177–5188 Flavin cofactors can be present as flavin adenine dinu- different oxidation reactions with exquisite chemoselectivity, cleotide (FAD) or, less often, as flavin mononucleotide regio- and/or enantioselectivity while merely using molecular (FMN) (Macheroux et al. 2011). In most flavoprotein oxi- oxygen as oxidant. The best-known flavoprotein oxidase is dases, the flavin is the sole cofactor, but in some oxidases, probably glucose oxidase, which has been produced and either FAD or FMN works in concert with another cofactor. applied already for several decades (Bankar et al. 2009). Other The catalytic cycle of flavoprotein oxidases consists of two known examples of applied oxidases are D-amino acid oxidase half reactions. In the reductive half reaction (step 1, Fig. 1), (Pollegioni et al. 2008), employed in synthesis of antibiotics, the organic substrate is oxidised by a two-electron transfer, and monoamine oxidases, used for the preparation of which results in a fully reduced flavin (hydroquinone), and enantiopure fine chemicals (Turner 2011). However, in the the oxidised product or product intermediate. For this half last decade, a large number of flavoprotein oxidases with other reaction, and analogous to nicotinamide-catalysed oxida- substrate scopes and reactivities have been discovered (Winter tions, a proper positioning of the substrate with respect to and Fraaije 2012). From detailed biochemical studies on these the reactive N5 atom of the flavin cofactor is required novel oxidases, new insights have been obtained on the cata- (Fraaije and Mattevi 2000). Regeneration of the oxidised lytic properties of these enzymes. Besides oxidases that are cofactor by dioxygen takes places in the subsequent oxida- able to catalyse relatively simple oxidations (for example the tive half reaction, which is a far-from-trivial reaction (steps oxidation of alcohols to aldehydes or ketones), also more 2 and 3, Fig. 1). In fact, the ability to use molecular oxygen complex oxidative reactions can be catalysed [for example as electron acceptor sets flavoprotein oxidases apart from all oxidative C–C bond formation by reticuline oxidase other flavoproteins. The reaction is spin forbidden because (Winkler et al. 2008)]. The architecture of the active site the electrons in dioxygen are in a triplet state. This restric- of each oxidase clearly determines its substrate acceptance tion is overcome by a stepwise electron transfer (Mattevi profile and oxidation reactivity. Moreover, the active site 2006). The redox potential of the oxidised flavin–hydroqui- also contains the structural requirements to allow oxygen none flavin couple varies between −400 and +120 mV in a to reach the flavin and to facilitate dioxygen reduction by protein environment, which is much lower than the potential the reduced cofactor (Baron et al. 2009). In some cases, of the dioxygen–hydrogen peroxide couple. As a result, the active site entails even an additional catalytic property: flavin-mediated oxidations that involve dioxygen as elec- It catalyses the formation of a covalent flavin-protein tron acceptor are thermodynamically favourable. Yet, the bond. By this, the flavin cofactor is covalently tethered protein microenvironment around the flavin cofactor deter- to the protein, preventing dissociation and increasing the mines how efficiently dioxygen can be utilised as electron redox potential (Fraaije et al. 1999) acceptor (Chaiyen et al. 2012). Comparison of the currently available flavoprotein oxi- The success of flavin-containing oxidases in biotechnolog- dase sequences and structures reveals that the oxidases ical applications is for a large part due to their interesting belong to several structurally distinct flavoprotein families. catalytic properties, as they can perform a wide variety of In this review, we provide an inventory of currently known Fig. 1 Catalytic cycle of the flavin cofactor in flavoprotein oxidases Appl Microbiol Biotechnol (2013) 97:5177–5188 5179 flavoprotein oxidases. Based