Seong et al. Appl Biol Chem (2019) 62:62 https://doi.org/10.1186/s13765-019-0469-6 INVITED REVIEW Open Access Enzymatic defuorination of fuorinated compounds Hyeon Jeong Seong†, Seong Woo Kwon†, Dong‑Cheol Seo, Jin‑Hyo Kim* and Yu‑Sin Jang* Abstract Fluorine‑containing compounds are widely used because they have properties required in textiles and coatings for electronic, automotive, and outdoor products. However, fuorinated compounds do not easily break down in nature, which has resulted in their accumulation in the environment as well as the human body. Recently, the enzymatic defuorination of fuorine‑containing compounds has gained increasing attention. Here, we review the enzymatic defuorination reactions of fuorinated compounds. Furthermore, we review the enzyme engineering strategies for cleaving C–F bonds, which have the highest dissociation energy found in organic compounds. Keywords: C–F bond, Defuorination, Fluorine, Perfuorinated compound Introduction and the corresponding enzymes, have not been well Because perfuorinated compounds (PFCs) repel both elucidated. water and oil, they are used as durable repellent treat- On the other hand, fuorinated compounds such as ments for textiles such as outdoor clothes and for home fuoroacetate and 5′-fuoro-5′-deoxyadenosine have been products such as carpets [1]. In addition, PFCs are widely identifed as natural products in nature [10, 11], dem- used in the production of fuoropolymers such as polyte- onstrating the existence of a biosynthesis pathway for trafuoroethylene (trade name, Tefon), which is widely fuorinated compounds in organisms [12]. A representa- used in coatings for electronic, automotive, and outdoor tive pathway of this type is the C–F bond forming reac- products [2]. tion catalyzed by Streptomyces cattleya fuorinase, which However, PFCs are harmful to both the natural envi- converts inorganic NaF into fuorinated compounds [10, ronment and humans as like other well-known pollut- 13, 14]. Fluorinase, 5′-fuoro-5′-deoxyadenosine syn- ants [1, 3–6]. Furthermore, PFCs are persistent materials thase, catalyzes the conversion of S-adenoxyl methio- that do not readily break down in natural environments nine to 5′-fuoro-5′-deoxyadenosine in S. cattleya (Fig. 1). [2]. Some PFCs accumulate in the human body, leading In addition to our knowledge of the enzymes catalyz- to an increase over time of the residual concentration of ing fuorination reactions, previous studies have also PFCs in the blood and organs [7]. For these reasons, the identifed enzymes involved in defuorination reactions biological decomposition of PFCs has gained increasing [15–19]. attention in recent times. Te biological transformation Here, we review the defuorination reactions of ali- of fuorotelomer alcohols (a type of PFC) was well sum- phatic and aromatic compounds containing fuorine by marized in several review papers [8, 9]. Nevertheless, native enzymes, including fuoroacetate dehalogenase, the biological pathways underlying PFC decomposition, fuoroacetate-specifc defuorinase, 4-fuorobenzo- ate dehalogenase, defuorinating enoyl-CoA hydratase/ *Correspondence: [email protected]; [email protected] hydrolase, 4-fuorophenol monooxygenase, and perox- †Hyeon Jeong Seong and Seong Woo Kwon contributed equally to this ygenase-like LmbB2. Furthermore, we review recently work developed enzyme engineering strategies for C–F bond Department of Agricultural Chemistry and Food Science Technology, Division of Applied Life Science (BK21 Plus Program), Institute cleavage, which give insights into the decomposition of of Agriculture & Life Science (IALS), Gyeongsang National University, fuorinated compounds. In this review, we do not discuss Jinju 52828, Republic of Korea rarely studied enzymes involved in the biotransformation © The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Seong et al. Appl Biol Chem (2019) 62:62 Page 2 of 8 Fig. 1 The fuorination reaction catalyzed by 5′‑fuoro‑5′‑deoxyadenosine synthase known as fuorinase [13, 14] Fig. 2 The catalytic triad Asp104, His271, and Asp128 on fuoroacetate dehalogenase [15] pathway, such as pyruvate dehydrogenase, maleylacetate parameters (kcat and KM) of Burkholderia fuoroacetate reductase, and enol-lactone isomerase [20–22]. dehalogenase have been known as 9.1 mM and 35 s−1 for fuoroacetate at 30 °C, while 15 mM and 1.5 s−1 for chlo- Defuorination by native enzymes roacetate [27]. Fluoroacetate dehalogenase Te frst three dimensional structure of fuoroacetate Although the dissociation energy of C–F bond is among dehalogenase was determined from Burkholderia sp. FA1 the highest found in nature, defuorination of fuoroac- in 2009 [15]. Te catalytic triad was identifed as Asp104, etate was identifed in microorganisms, such as Burk- His271, and Asp128 (Fig. 2). Carboxyl group of Asp104 holderia, Pseudomonas, Delftia, Rhodopseudomonas, and was suggested as a nucleophile to attack the alpha carbon Moraxella [23–26]. Te C–F bond on fuoroacetate can on fuoroacetate in an SN2 reaction. By this nucleophilic be cleaved by fuoroacetate dehalogenase in such micro- attack, fuoride ion is released from fuoroacetate, while organisms [15]. Fluoroacetate dehalogenase functions to enzyme–substrate (ES) ester intermediate is formed. the cleavage of C–Cl bond as well as C–F bond. Kinetic In subsequent, the resulting ES ester intermediate is Seong et al. Appl Biol Chem (2019) 62:62 Page 3 of 8 hydrolyzed by H2O which is the second nucleophile acti- defuorination reaction [30]. Furthermore, the pocket vated by His271. In a later study using quantum mechan- is delicately balanced for fuorine, the smaller halogen ical/molecular mechanical (QM/MM) calculations, it is atom, for the selectivity of fuoroacetate [30]. revealed that two Arg residues at 105th and 108th posi- tions are interacted with carboxyl group of fuoroacetate Fluoroacetate‑specifc defuorinase by hydrogen bond [28]. His149, Trp150, and Tyr212 sta- Fluoroacetate-specifc defuorinase has been identifed bilize fuorine atom via hydrogen bond, which results in in mammals that lives in area where plants capable of reduction of activation energy [28]. forming fuoroacetate grow [16]. Tese mammals detox- In terms of the substrate specifcity of fuoroacetate ify fuoroacetate by fuoroacetate-specifc defuorinase. dehalogenase, the importance of Trp150 was asserted by Fluoroacetate-specifc defuorinase has been purifed mutation of the amino acid residue [15]. Te Trp150Phe from liver cytosol in mouse and rat [31, 32]. Te defuori- mutation resulted in the complete loss of defuorination nation mechanism of fuoroacetate-specifc defuori- activity without the lack of dechlorination activity [15]. nase is difer from that of fuoroacetate dehalogenase: In a later study using docking simulation and QM/MM glutathione is involved in the defuorination reaction by calculations, it was suggested that the conformational fuoroacetate-specifc defuorinase (Fig. 3). Fluoroace- change for SN2 reaction is favorable in C–F bond rather tate-specifc defuorinase showed similar characteristics than C–Cl bond [27, 29]. In the simulation, chloroacetate to glutathione S-transferase (GST) theta and zeta classes did not form the reactive conformation for S N2 reac- in liver cytosol (GSTT and GSTZ, respectively) [33, 34]. tion, because of the longer C–Cl bond [27]. In another Te defnition of fuoroacetate-specifc defuorinase study, crystal structures of a Rhodopseudomonas palus- is still controversial. In a recent study, GSTZ (exactly tris fuoroacetate dehalogenase was determined along GSTZ1C) has showed the highest fuoroacetate-specifc the defuorination reaction of fuoroacetate [30]. In such defuorinase among all GST isozymes, which is just 3% study, Chan and coworkers reported a halide pocket to of the total activity of fuoroacetate-specifc defuorinase support three hydrogen bonds which stabilize the fuo- determined in cytosol [35]. Kinetic parameters (V max ride ion in the fuoroacetate dehalogenase-mediated and KM) of fuoroacetate-specifc defuorinase activity Fig. 3 Defuorination mechanism of fuoroacetate by fuoroacetate‑specifc defuorinase [31–34] Seong et al. Appl Biol Chem (2019) 62:62 Page 4 of 8 in rat cytosol have been reported as 27.7 mmol F −/mg Defuorination of 4-fuorobenzoate and 2-fuoroben- protein/h and 3.8 mM for fuoroacetate [35]. In another zoate is catalyzed by 4-fuorobenzoate dehalogenase study, novel fuoroacetate-specifc defuorinase, FSD1 [17] and defuorinating enoyl-CoA hydratase/hydrolase was isolated from rat hepatic cytosol [32]. FSD1 showed [18], respectively. However, the defuorination mecha- 81% of the total cytosolic activity of fuoroacetate-specifc nism of two enzymes is quite difer from each other. In defuorinase, without GST activity [32]. FSD1 showed the reaction catalyzed by 4-fuorobenzoate dehalogenase, about 60% similarity to sorbitol dehydrogenase in amino defuorination of 4-fuorobenzoate is directly conducted acid sequence, although defuorination activity of sorbi- without the structural transformation, which was sug- tol dehydrogenase has not been reported [32]. gested by Oltmanns and coworkers [17]. Te research group determined fuoride ion and trace amounts of Enzymes