Carcinogenic Metabolic Activation Process of Naphthalene by the

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Carcinogenic Metabolic Activation Process of Naphthalene by the Cytochrome P450 Enzyme 1B1: A Computational Study Lei Bao, Wen Liu, Yanwei Li, Xueyu Wang, Fei Xu, Zhongyue Yang, Yue Yue, Chenpeng Zuo, Qingzhu Zhang, and Wenxing Wang Chem. Res. Toxicol., Just Accepted Manuscript • DOI: 10.1021/acs.chemrestox.8b00297 • Publication Date (Web): 22 Feb 2019 Downloaded from http://pubs.acs.org on February 25, 2019

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Chemical Research in Toxicology

Carcinogenic Metabolic Activation Process of Naphthalene by the Cytochrome P450 Enzyme 1B1: A Computational Study Lei Bao‡, Wen Liu‡, Yanwei Li*‡, Xueyu Wang‡, Fei Xu※, Zhongyue Yang§, Yue Yue‡, Chenpeng Zuo‡, Qingzhu Zhang*‡, Wenxing Wang‡ ‡

Environment Research Institute, Shandong University, Qingdao 266237, P. R. China

※

Shenzhen Research Institute of Shandong University, Shenzhen 518057, P. R. China §

Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States

Keywords QM/MM, DFT, Naphthalene, Cytochrome P450 Enzyme 1B1, Electrophilic addition, Epoxidation _________________________________________________________ *Corresponding authors. E-mail: [email protected], [email protected]

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Chemical Research in Toxicology 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Abstract The metabolic activation and transformation of naphthalene by cytochrome P450 enzyme (CYP 1B1) plays an important role in its potential carcinogenicity. The process has been explored by a quantum mechanics/molecular mechanics (QM/MM) computational method. Molecular dynamic simulations were performed to explore the interaction between naphthalene and CYP 1B1. Naphthalene involves α- and β-carbon, the electrophilic addition of which would result in different reaction pathways. Our computational results show that both additions on α- and β-carbon can generate naphthalene 1,2-oxide. The activation barrier for the addition on β-carbon is higher than that for the α-carbon by 2.6 kcal∙mol-1, which is possibly caused by the proximity between β-carbon and the iron-oxo group of Cpd I in the system. We also found that naphthalene 1,2-oxide is unstable and the O-C bond cleavage easily occur by cellular hydronium ion, hydroxyl radical / anion, then it will convert to the potential ultimate carcinogen 1,2-naphthoquinone. The results demonstrate and inform the detailed process of generating naphthalene 1,2-oxide and new predictions for its conversion.



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Introduction

Polycyclic aromatic hydrocarbons (PAHs) are volatile organic pollutants produced from the incomplete combustion or biosynthesis of wood, petroleum, and other organic materials1. They are formed by the condensation of two or more benzene rings or cyclopentadiene2. Most of PAHs are identified as early human environmental carcinogens. For instance, the most “simple” PAHs in structure, naphthalene, is classified as a category of 2B carcinogen by the International Agency for Research on Cancer (IARC) of the World Health Organization. Naphthalene is the main contributor of air pollution caused by PAHs3, 4. Naphthalene is easily accumulated in the sediment and organic matter5, and can migrate in the environment6. Once absorbed by flora and fauna and entering the food chain7, naphthalene may cause severe human health issues. Besides its presence in the atmosphere, naphthalene is also one of the main components of the mothball and can affect the indoor environment directly or indirectly8. Previous

studies

have

confirmed

that

alveolar/bronchiolar adenomas effects in

naphthalene

exerts

male mice after two

pulmonary years of

naphthalene-absorption toxicology tests, and carcinogenic activity was found in female mice9. Later, it was found that the toxicity of naphthalene depends on the biological activity of its metabolites, which are potentially carcinogenic to humans. Cytochrome enzymes (P450 enzymes) play an important role in the oxidation of naphthalene10-12. Besides naphthalene, most PAHs are activated by P450 enzymes in the human body. There are numerous types of P450 enzymes, among which the A, B,


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F subfamilies are most responsible for generating carcinogenic metabolites, with CYP1A1, CYP1B1, and CYP2F1 being several representatives13-16. However, there are still uncertainties in the carcinogenicity of naphthalene. Studies show that the tumor inducing effect was not obvious during the course that naphthalene or any of its metabolites caused genetic damage17. The metabolic mechanism of naphthalene catalyzed by the P450 enzymes has been proposed: the initial metabolite is proposed to be 1,2-napthalene epoxide18, which can be detoxified through glutathione metabolism19, meanwhile, it can also be converted to naphthoquinone producing carcinogenic toxicity by P450 enzymes, epoxide hydrolase or aldehydes reductase12,

20

. Although experiments have

conjectured or verified some naphthalene metabolites (naphthalene 1,2-oxide, 1,2-naphthoquinone) and their interactions with DNA21-23, the detailed process for the formation of naphthalene 1,2-oxide has not been fully resolved18, 24, 25. The activation mechanism of naphthalene in human P450 enzymes is thus of great importance to understand. Theoretical calculation provides an effective approach to elucidate the atomic-level molecular mechanism. Particularly, extensive computational studies have been performed to understand the roles of P450 enzymes26. Both QM and QM/MM methods have been widely used in studying P450 enzymes. Combined QM and QM/MM simulations on the catalytic activation of benzene by P450 enzymes suggested that two intermediates, epoxides and ketones/phenols, may coexist27, 28. The epoxide intermediates are carcinogenic metabolites. Ketones/phenols are formed through a so-called NIH (National Institutes of Health) pathway where a proton



transfer between carbons of benzene is involved. Another study indicates that the proton may also shift to the porphyrin ring29. A recent new study shows that the epoxidation intermediate channel is more advantageous than the phenolic intermediate30. In the study of P450 enzyme-activated metabolism of polybrominated diphenyl ethers, the NIH channel was found to be a competitive pathway with the epoxidation channel31, 32. Moreover, the significance of P450 enzymes metabolically activating pollutants or drugs through hydroxylation and epoxidation have been revealed in recent studies33-36. Here we applied the “state-of-the-art” QM/MM method to study the metabolic activation of naphthalene in human P450 enzymes to understand how carcinogenic intermediate metabolite naphthalene 1,2-oxide is generated. The results highlight that the activation mainly involves two steps: electrophilic addition and epoxidation. This provide mechanistic understanding to the metabolic carcinogenic activation of condensed-ring compounds. We also investigated the reactions of the intermediate naphthalene 1,2-oxide with ubiquitous cellular H2O molecule and OH radical in the simulated enzyme environment to verify its instability by DFT-only method. These will inform further carcinogenicity of naphthalene, helping us introspect the environmental effects and health risks for naphthalene.

Computational Details

Molecular Dynamics Simulation

Since there is no crystal structure of naphthalene and CYP1B1 complexes, the


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model was built on the basis of the human cytochrome CYP1B1 and α-naphthoflavone complexes obtained from the protein database (www.rcsb.org, PDB code 3PM0, a resolution of 2.7 Å), α-naphthoflavone contains a naphthalene and is a reliable initialized structure that can be modified, namely, its other part is removed to get the substrate naphthalene. The Cpd I is the active specie of the active center of the CYP1B1 enzyme26. The CHARMM force field37-39 was used to add the hydrogen atoms required for the crystal structure, and the enzyme complex was dissolved in a water model (TIP3P)40 with a radius of 35 Å. After the energy was optimized, the water molecules in the system were randomly substituted with sodium ion to neutralize the entire system. The entire system was heated from absolute zero to 298.15 K within 50 ps, and then reached thermal equilibrium at a time node (1 fs/step) of about 500 ps. Afterwards, a stochastic boundary molecular dynamics (SBMD) simulation of 20 ns was performed at 298.15 K, which utilizes an NVT ensemble for conformation sampling41. During the SBMD simulation, the entire system was free to move and the coordinates are not limited, so that it was consistent with the position in the crystal structure. And the frog-jumping algorithm of the CHARMM program and the Langevin temperature coupling method was used to perform the reaction fitting. Different time nodes were randomly selected from molecular dynamics simulations for subsequent QM/MM calculations.

QM/MM Calculation

The computations were performed on the ChemShell36 platform42, which



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integrates the program Turbomole43 and DL-POLY44. The charge shift model45 and the electrostatic embedding method46 were applied during QM/MM calculations. Using the trace geometry optimization to do the transition state search, a single-point energy calculation and potential energy analysis are completed. The energy calculations were performed on the LACV3P+*(Fe)/B3LYP-D3/6-311++G**(C, H, O, N, S) level, which can well reproduce the experimental results from previous studies47-49. For the entire system, density functionals and basis set and methods were used in peer-relevant research work and proved to be feasible29,

31, 50

. All these

allowed us to better analyze the mechanism of action and the reaction pathway of naphthalene and its derivatives and the CYP 1B1 enzyme. About 15 conformations were randomly selected from 20 ns trajectory for the QM/MM calculations. The QM region included a heme group (codenamed Cpd I) with no substituent on the porphyrin ring, cysteine attached to the porphyrin ring, and the substrate naphthalene (codenamed NAP). The MM region contained about 23000 atoms, and the QM region contained approximately 75 atoms of which the number of unpaired electrons is 1.

DFT Calculation

Structural optimization and energy calculations were carried out using the Gaussian09 program at two levels of theory method. For geometry optimization of reaction species, the B3LYP functional with a basis set of 6-31G** (C, H, O), and for single-point energy calculations, a high-level basis set, 6-311++G** (C, H, O) was implemented. Frequency calculations were performed at the B3LYP/6-31G** level to


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characterize atomic vibration modes and obtain zero-point energies (ZPE). Solvation effects were evaluated with the PCM continuum-solvation (water) model51 at the same level of theory in geometry optimization and energy calculation. Some works that utilized the implicit solvent model in DFT calculations of interaction between Cpd I and organic pollutants have justified its reliability in reflecting the situation in enzyme52, 53. We also compared the performance of M062X and B3LYP, the results showed that B3LYP performed more prominent than M062X in estimating geometry and energy (detail in table S1 of the Supporting Information, SI).

Results and Discussion

Molecular Dynamics

MD simulations were performed for 20 ns. The distances of Fe-O, O-C3 and O-C4 fluctuate around 1.63, 3.30 and 4.00 Å (SI Figure S1), which is consistent with previous studies54-56. No restrains were applied during the molecular dynamics simulations which allow us to probe whether there are large translations and rotations of naphthalene in the active center of human P450. Balthelt et al. pointed out that there were two different binding modes (Face-on and Side-on) for benzene in the active site of human P450, and they also showed that these two modes share similar activation energies (~20.0 kcal∙mol-1)27. However, naphthalene is much larger than benzene, its translations and rotations are limited to a certain range of areas. As shown in Figure 1, residues such as Gly, Ala, Phe, Ile, Leu, Thr, Val, Asp are within 5 Å of the



naphthalene ring, and the maximum distance between any two carbons of the naphthalene ring is 5.04 Å. Thus, naphthalene must overcome strong steric hindrance and electrostatic effects to make large rotations. Changes in the spatial conformation of the system suggest that other PAHs having more benzene rings than naphthalene may also be difficult to undergo large positional change during the catalysis by P450 enzymes. Through the MD study, the basic structural requirements of naphthalene binding in the active center of CYP1B1 have been revealed.

Electrophilic Addition

Based on the molecular dynamic trajectories, 15 conformations were selected (every 1~2 ns) for the following QM/MM calculations. Naphthalene has two different carbons: Cα and Cβ (correspond respectively as C4 and C3 in SI Figure S2). No experimental and theoretical studies have been performed to reveal the atomic detail of the naphthalene oxidation process57. It has been reported that the low-energy reaction channels of the Cpd I electrophilic attacking on the benzene molecule occur in the doublet state under the catalysis of P450 enzymes29. Here the results were confirmed that doublet state is much lower when attacking on either C3 or C4 for naphthalene. In order to understand the intrinsic catalytic preference, 15 conformations for Cpd I attacking on C4 and C3 were calculated, which result in 30 reaction pathways. The lowest energy path of attacking C4 occurs in the snapshot taken at the 10 ns, the activation energy fluctuates between 14.6-27.9 kcal∙mol-1 (Table 1). And the lowest energy barrier path of C3 is 15


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ns, the activation energy fluctuates between 11.5-16.8 kcal∙mol-1 (Table 1). Noticeably, energetics computed from one single snapshot is unable to reflect the reaction process catalyzed by enzymes. Statistical distribution of the two 15 pathways shows that these energy barriers have distributional stability and feasibility. We found that the barriers of two addition paths have a distribution interval respectively, the major barriers of addition on C4 are 20-26 kcal∙mol-1, the major barriers of addition on C3 are 12-15 kcal∙mol-1 (SI Figure S3, a, b). Then Boltzmann averaging barrier (SI Method S1) for attacking on C3 is 12.5 kcal∙mol-1, and that for C4 is 15.1 kcal mol-1, the average activation energy of attacking on C3 is generally lower than C4 of 2.6 kcal∙mol-1. As for bond distance and bond angle, MD and QM/MM calculation show that the variation trend of O-C4 distance is relatively proportional to that of O-C3 distance (Figure 2, a), meanwhile, the variation of Fe-O-C4 angle is relatively proportional to that of Fe-O-C3 angle (Figure 2, b). The size of two angles increase with O approaching C3 and C4 (Figure 2, c, d), and no strong correlation is found between the barrier and distance or angle. There are some deviations of distance angle relationship between QM/MM and MD in the four graphs. Electronic property is also an important factor affecting electrophilic reactions. The negative atomic charge usually leads to relatively strong electron withdrawing ability that promotes electrophilic process58, 59. The whole electrophilic attack process in the snapshot taken at 10 ns was further probed (Figure 3) from electronic structure perspective. The overall charge (calculated detail is showed with SI Method S2) of C3 is more negative than that of C4 indicating that the bound Cpd I is more possible to



electrophilically attack on C3. The charge comparing of all the selected snapshots are shown with SI Figure S2, d. For comparison, we have optimized the naphthalene molecule respectively in vacuum, water and active site in the same base group (SI Figure S2 a, b) and find that both the charge of C4 and C3 are positive than that in the P450 enzyme active site (SI Figure S2, c). This also reflects that the electronic properties of naphthalene were influenced by the enzyme when it enters the enzymatic system. More electronic data and analysis are provided in SI table S2, S3. Thus, it is concluded that C3 and C4 are two potent competitive targets in the electrophilic addition of Cpd I attacking on the naphthalene based on our calculation. We also need to mention that the initial PDB structure used in this study could have impact on the conclusion, albeit that molecular dynamics simulation has been carried out. Although the X-ray crystal structure is stable (and should be the most stable)60, it is not necessarily the only stable conformation. In this respect, therefore, the initial PDB structure may exert an influence, but it isn’t the focus of our research. Considering the balance between computational cost and conformational selection, we also may not have explored all the conformations of the initial structure. Our computation offers a perspective that the conformation of enzymatic active center influences strongly the reaction mechanism.

Epoxidation Strategies

After determining the process of electrophilic addition from Cpd I to naphthene, the next question is how the naphthalene epoxidation actually happens. This is also an


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important step in the activation of naphthalene metabolism, like the xenobiotic metabolism of other compounds53, 61. The formation of naphthalene 1,2-oxide metabolic intermediates was shown in scheme 1. There are two possible pathways to form the final product: IM-1→P or IM-2→P (Scheme 1). The energy barriers required for the formation of naphthalene 1,2-oxide at C4 site are lower than those at C3 for the two epoxides. For the 10 ns snapshot, the epoxidation barrier at C4 is -0.3 kcal∙mol-1, while at C3 it is 2.4 kcal∙mol-1. For the snapshot taken at the 15 ns, the epoxidation barrier at C 4 is 2.8 kcal∙mol-1, while at C3 it is 8.2 kcal∙mol-1 (Figure 4). The epoxidation process of the two snapshots may be a diffusion-controlled reaction, as the barrier is below or close to the upper limit of enzyme-substrate reaction62, 63 The results show that naphthalene 1,2-oxide can be generated from both additive sites with comparable energetics. It also suggests that the formation of 1,2-napthalene epoxide is rapid under the catalysis of Cpd I. In addition, it is worth mentioning that neither of the two lowest barrier paths captured naphthalene 2,3-oxide, the intermediate isn’t also observed in experiments11, 12. Other hydroxylation routes for both snapshots are also calculated. The activation energy required for H atom migrating to the porphyrin ring is higher than that for epoxidation, and there is a competitive relationship between NIH (H atom shift to C atom of ortho-position) and epoxidation pathway (SI Figure S4). The supplementary barriers diagram of the quartet state is shown in SI Figure S5. The naphthalene 1,2-oxide can be converted without the catalysis of P450 enzyme64. Here we calculated the ring-opening course of naphthalene 1,2-oxide under



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the action of hydroxyl radical (one of important reactive oxygen species (ROS) in living systems65, 66) and water molecule, hydronium ion67, 68

(easily forming by a

proton and water molecule ) and hydroxyl anion that are ubiquitous in vivo. The Naphthalene 1,2-oxide opens ring with the aid of hydronium ion or hydroxyl radical / anion, by either O-C3 bond or O-C4 bond cleavage. The activation barrier of O-C3 or O-C4 bond cleavage by hydroxyl radical is around 14 kcal∙mol-1 (about 2 kcal∙mol-1 higher than by hydroxyl anion, SI Table S4). Notably, the ring-opening process involving hydronium ion is barrierless, and the intermediate can quickly generate 1,2-hydro-1,2-naphthalenediol when it further combines with hydroxyl anion (Figure 5). As for the process involving hydroxyl radical, the H atom of hydroxyl carbon can shift to carbonyl radicals on adjacent carbon in the second step involved a water molecule. Then they produce 1/2-hydro-1,2-naphthalenediol radical, both of the two reactions require energy barrier that are not more than 10.0 kcal∙mol-1. The two free radicals will finally convert to 1,2-naphthalenediol with the participation of hydroxyl radical, and the process is barrierless (Figure 5). We also found that the naphthalene 1,2-oxide ring cannot be opened spontaneously. In brief, naphthalene 1,2-oxide can easily generate 1,2-hydro-1,2-naphthalenediol by hydronium ion and hydroxyl anion and then convert to 1,2-naphthalenediol probably by catechol reductase12, it also may directly form 1,2-naphthalenediol in the cell where hydroxyl radical and water is abundant (SI Scheme S1). Then them finally produce genotoxic 1,2-naphthoquinone. Our calculations confirm that hydronium ion, hydroxyl radical / anion and water may be involved in the carcinogenic metabolic activation of naphthalene, and show that the


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metabolic intermediate naphthalene 1,2-oxide are unstable with a half-life of above 1~5 ms, which explains why it hard to be detected or isolated in experiment 69. These computations were done using implicit solvent model. More accurate and realistic models would be expected to establish under explicit solvent environment70, 71.

Toxicological Implication

The work focuses on the process of naphthalene to naphthalene 1,2-oxide catalyzed by P450 enzymes. It has been found that the ability to form epoxides through two additive sites is comparable, that is, in this computation the Cβ has a narrowly advantage over Cα. Therefore, we think the reason should be considered is that the spatial structure of pollutants in the enzyme system has certain effects on their metabolic activation, and the enzyme in turn may change the properties of pollutants to a certain extent. 1,2-naphthalenediol is formed from naphthalene 1,2-oxide under the action of epoxide hydrolase and catechol reductase, it also be generated with participation of OH radical and H2O molecule though our study. Experiments had reports on P450 enzymes metabolizing naphthalene. Ross et al72 pointed out that CYP 1B1 plays a key role for the activation of carcinogen PAHs. Hall et al73 claimed naphthalene holds a low level of metabolites generated 1- and 2-naphthol in the CYP 101B1 system. Fukami et al64 reported that CYP 2A13 oxidize naphthalene efficiently, the major primarily is 1-naphtol, not 2-naphthol, Shimada et al69 stated that CYP 2A6 could involve in the process and CYP 1A2, 1B1, 3A4 and so on have a role in oxidizing



naphthalene. CYP 3A4 is the most effective P450 isoform for 2-naphthol production and CYP 1A2 is the most efficient for producing dihydrodiol and 1-naphthol through the work of Cho et al74. Different subfamilies have different metabolic orientation, the formation of ultimate carcinogen naphthoquinone may be in a multi-enzyme environment. And some work demonstrated that naphthalene and its derivatives could interact rapidly with CYP 1B175-77. The process of naphthalene 1,2-oxide formation and conversion maybe efficient, which is confirmed by our computation. The addition behavior to differ-property carbon to generate the intermediate need further experimental investigation. The carcinogenic and metabolic activation of foreign pollutants may occur under a combination of different conditions in a complex human environment, so more factors need to be considered in future studies. Our next work is to study the interaction between 1,2-naphthoquinone and DNA to explore the reaction mechanism at the molecular level in view of the uncertainty of carcinogenesis of naphthalene. This current calculation not only provide a detailed description of the formation process of naphthalene 1,2-oxide, but also provide new predictions for its conversion. The results serve as a basis for future studies on the carcinogenesis and activation of naphthalene.

Acknowledgements

The work was financially supported by National Natural Science Foundation of China (Nos. 21577082, 21507073 and 91644214), the National Major Science and


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Technology

Program

for

Water

Pollution

Control

and

Treatment

(No.

2017ZX07202-002), Young Scholars Program of Shandong University (No. 2018WLJH54) and Taishan Scholars (No. ts201712003), Shenzhen science and technology research and development funds (JCYJ20160510165106371).

Supporting Information

The comparison of activation barrier of bond(O-C3) cleavage under basis B3LYP and M062X

(Table

S1),

two

supplementary

description

of

methods

of

Boltzmann-weighted Average and Charge Distribution Analysis (Method S1, S2), RMSD and distance variations analysis of MD simulation (Figure S1), NPA charge of naphthalene (Figure S2), distribution analysis of attacking energy barriers(Figure S3), other related potential energy profiles(Figure S4, S5), the process of ring-opening of naphthalene 1,2-oxide and formation of 1,2-naphthalenediol scheme (Figure S6), electronics data of the addition process(Table S2, S3), energy barriers of the ring-opening of naphthalene 1,2-oxide under the effect of hydroxide ion (Table S4), and Cartesian coordinates for all reaction species in snapshot 10ns. Two links of dynamic graph of MD and the process of epoxide formation in two addition modes in snapshot 10ns.S

References (1) Howsam, M. and Jones, K. C. (1998) Sources of PAHs in the environment. Springer 137-174. (2) Kim, K. H., Jahan, S. A., Kabir, E. and Brown, R. J. (2013) A review of airborne polycyclic aromatic hydrocarbons (PAHs) and their human health effects. Environ. Int. 60, 71-80.



(3) Samanta, S. K., Singh, O. V. and Jain, R. K. (2002) Polycyclic aromatic hydrocarbons: environmental pollution and bioremediation. Trends Biotechnol. 20, 243-248. (4) Xu, F., Shi, X., Zhang, Q. and Wang, W. (2016) Mechanism for the growth of polycyclic aromatic hydrocarbons from the reactions of naphthalene with cyclopentadienyl and indenyl. Chemosphere 162, 345-54. (5) Xing, B. (2001) Sorption of naphthalene and phenanthrene by soil humic acids. Environ. Pollut. 111, 303-309. (6) Lunde, G. and Bjorseth, A. L. F. (1977) Polycyclic aromatic hydrocarbons in long-range transported aerosols. Nature 268, 518. (7) Simonich, S. L. and Hites, R. A. (1994) Importance of vegetation in removing polycyclic aromatic hydrocarbons from the atmosphere. Nature 370, 49. (8) World Health Oganization. (2010) WHO guidelines for indoor air quality: selected pollutants. (9) Abdo, K. M., Eustis, S. L., McDonald, M., Jokinen, M. P., Adkins, B. and Haseman, J. K. (1992) Naphthalene: A Respiratory Tract Toxicant and Carcinogen for Mice. Inhal. Toxicol. 4, 393-409. (10) Brusick, D., Small, M. S., Cavalieri, E. L., Chakravarti, D., Ding, X., Longfellow, D. G., Nakamura, J., Rogan, E. C. and Swenberg, J. A. (2008) Possible genotoxic modes of action for naphthalene. Regul. Toxicol. Pharmacol. 51, S43-50. (11) Buckpitt, A., Boland, B., Isbell, M., Morin, D., Shultz, M., Baldwin, R., Chan, K., Karlsson, A., Lin, C. and Taff, A. (2002) Naphthalene-induced respiratory tract toxicity: metabolic mechanisms of toxicity. Drug Metab. Rev. 34, 791-820. (12) Schreiner, C. (2003) Genetic Toxicity of Naphthalene: A Review. J. Toxicol. Chem. Environ. Health B 6, 161-183. (13) Go, R. E., Hwang, K. A. and Choi, K. C. (2015) Cytochrome P450 1 family and cancers. J. Steroid Biochem. Mol. Bio. 147, 24-30. (14) Guengerich, F. P. (2015) Human cytochrome P450 enzymes. Springer 523-785. (15) Nelson, D. R., Kamataki, T., Waxman, D. J., Guengerich, F. P., Estabrook, R. W., Feyereisen, R., Gonzalez, F. J., Coon, M. J., Gunsalus, I. C. and Gotoh, O. (1993) The P450 superfamily: update on new sequences, gene mapping, accession numbers, early trivial names of enzymes, and nomenclature. DNA Cell Biol. 12, 1-51. (16) Shimada, T., Oda, Y., Gillam, E. M. J., Guengerich, F. P. and Inoue, K. (2001) Metabolic activation of polycyclic aromatic hydrocarbons and other procarcinogens by cytochromes P450 1A1 and P450 1B1 allelic variants and other human cytochromes P450 in Salmonella typhimurium NM2009. Drug Metab. Dispos. 29, 1176-1182. (17) Bailey, L. A., Nascarella, M. A., Kerper, L. E. and Rhomberg, L. R. (2016) Hypothesis-based weight-of-evidence evaluation and risk assessment for naphthalene carcinogenesis. Crit. Rev. Toxicol. 46, 1-42. (18) Jerina, D. M., Daly, J. W., Witkop, B., Zaltzman-Nirenberg, P. and Udenfriend, S. (1970) 1, 2-Naphthalene oxide as an intermediate in the microsomal hydroxylation of naphthalene. V. Biochemistry 9, 147-156. (19) Buckpitt, A. R. and Bahnson, L. S. (1986) Naphthalene metabolism by human lung microsomal enzymes. Toxicology 41, 333-341. (20) Saeed, M., Higginbotham, S., Rogan, E. and Cavalieri, E. (2007) Formation of


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depurinating N3adenine and N7guanine adducts after reaction of 1,2-naphthoquinone or enzyme-activated 1,2-dihydroxynaphthalene with DNA: Implications for the mechanism of tumor initiation by naphthalene. Chem. Biol. Interact. 165, 175-88. (21) Klotz, K. and Angerer, J. (2016) Quantification of naphthoquinone mercapturic acids in urine as biomarkers of naphthalene exposure. J. Chromatogr. B 1012-1013, 89-96. (22) Kuusimaki, L., Peltonen, Y., Mutanen, P., Peltonen, K. and Savela, K. (2004) Urinary hydroxy-metabolites of naphthalene, phenanthrene and pyrene as markers of exposure to diesel exhaust. Int. Arch. Occup. Environ. Health 77, 23-30. (23) Ohnishi, S., Hiraku, Y., Hasegawa, K., Hirakawa, K., Oikawa, S., Murata, M. and Kawanishi, S. (2018) Mechanism of oxidative DNA damage induced by metabolites of carcinogenic naphthalene. Mutat. Res. 827, 42-49. (24) Guengerich, F. P. (2007) Cytochrome p450 and chemical toxicology. Chem. Res. Toxicol. 21, 70-83. (25) Zhang, X. and Li, S. (2017) Expansion of chemical space for natural products by uncommon P450 reactions. Nat. Prod. Rep. 34, 1061-1089. (26) Shaik, S., Cohen, S., Wang, Y., Chen, H., Kumar, D. and Thiel, W. (2010) P450 Enzymes: Their Structure, Reactivity, and Selectivity—Modeled by QM/MM Calculations. Chem. Rev. 110, 949-1017. (27) Bathelt, C. M., Mulholland, A. J. and Harvey, J. N. (2008) QM/MM modeling of benzene hydroxylation in human cytochrome P450 2C9. J. Phys. Chem. A 112, 13149-13156. (28) Bathelt, C. M., Ridder, L., Mulholland, A. J. and Harvey, J. N. (2004) Mechanism and structure-reactivity relationships for aromatic hydroxylation by cytochrome P450. Org. Biomol. Chem. 2, 2998-3005. (29) de Visser, S. P. and Shaik, S. (2003) A proton-shuttle mechanism mediated by the porphyrin in benzene hydroxylation by cytochrome P450 enzymes. J. Am. Chem. Soc. 125, 7413-7424. (30) Gupta, R., Li, X. X., Cho, K. B., Guo, M., Lee, Y. M., Wang, Y., Fukuzumi, S. and Nam, W. (2017) Tunneling Effect That Changes the Reaction Pathway from Epoxidation to Hydroxylation in the Oxidation of Cyclohexene by a Compound I Model of Cytochrome P450. J. Phys. Chem. Lett. 8, 1557-1561. (31) Fu, Z., Wang, Y., Chen, J., Wang, Z. and Wang, X. (2016) How PBDEs Are Transformed into Dihydroxylated and Dioxin Metabolites Catalyzed by the Active Center of Cytochrome P450s: A DFT Study. Environ. Sci. Technol. 50, 8155-63. (32) Wang, X., Wang, Y., Chen, J., Ma, Y., Zhou, J. and Fu, Z. (2012) Computational toxicological investigation on the mechanism and pathways of xenobiotics metabolized by cytochrome P450: a case of BDE-47. Environ. Sci. Technol. 46, 5126-33. (33) Amaya, G. M., Durandis, R., Bourgeois, D. S., Perkins, J. A., Abouda, A. A., Wines, K. J., Mohamud, M., Starks, S. A., Daniels, R. N. and Jackson, K. D. (2018) Cytochromes P450 1A2 and 3A4 Catalyze the Metabolic Activation of Sunitinib. Chem. Res. Toxicol. 31, 570-584. (34) Hankinson, O. (2016) The role of AHR-inducible cytochrome P450s in metabolism of polyunsaturated fatty acids. Drug Metab. Rev. 48, 342-350. (35) Jaladanki, C. K., Shaikh, A. and Bharatam, P. V. (2017) Biotransformation of Isoniazid by Cytochromes P450: Analyzing the Molecular Mechanism using Density Functional Theory.



Chem. Res. Toxicol. 30, 2060-2073. (36) Lábas, A., Krámos, B. and Oláh, J. (2017) Combined Docking and Quantum Chemical Study on CYP-Mediated Metabolism of Estrogens in Man. Chem. Res. Toxicol. 30, 583-594. (37) Brooks, B. R., Brooks Iii, C. L., Mackerell Jr, A. D., Nilsson, L., Petrella, R. J., Roux, B. t., Won, Y., Archontis, G., Bartels, C. and Boresch, S. (2009) CHARMM: the biomolecular simulation program. J. Comput. Chem. 30, 1545-1614. (38) Brooks, B. R., Bruccoleri, R. E., Olafson, B. D., States, D. J., Swaminathan, S. a. and Karplus, M. (1983) CHARMM: a program for macromolecular energy, minimization, and dynamics calculations. J. Comput. Chem. 4, 187-217. (39) Karplus, M. and McCammon, J. A. (2002) Molecular dynamics simulations of biomolecules. Nat. Struct. Mol. Biol. 9, 646. (40) Jorgensen, W. L., Chandrasekhar, J., Madura, J. D., Impey, R. W. and Klein, M. L. (1983) Comparison of simple potential functions for simulating liquid water. J. Chem. Phy. 79, 926-935. (41) Brooks Iii, C. L. and Karplus, M. (1983) Deformable stochastic boundaries in molecular dynamics. J. Chem. Phy. 79, 6312-6325. (42) Sherwood, P., de Vries, A. H., Guest, M. F., Schreckenbach, G., Catlow, C. R. A., French, S. A., Sokol, A. A., Bromley, S. T., Thiel, W. and Turner, A. J. (2003) QUASI: A general purpose implementation of the QM/MM approach and its application to problems in catalysis. J. Mol. Struct.: THEOCHEM 632, 1-28. (43) Ahlrichs, R., Bär, M., Häser, M., Horn, H. and Kölmel, C. (1989) Electronic structure calculations on workstation computers: The program system turbomole. Chem. Phys. Lett. 162, 165-169. (44) Smith, W. and Forester, T. R. (1996) DL_POLY_2.0: A general-purpose parallel molecular dynamics simulation package. J. Mol. Graph. 14, 136-141. (45) De Vries, A. H., Sherwood, P., Collins, S. J., Rigby, A. M., Rigutto, M. and Kramer, G. J. (1999) Zeolite structure and reactivity by combined quantum-chemical-classical calculations. J. Phys. Chem. B 103, 6133-6141. (46) Bakowies, D. and Thiel, W. (1996) Hybrid models for combined quantum mechanical and molecular mechanical approaches. J. Phys. Chem. 100, 10580-10594. (47) Lonsdale, R., Harvey, J. N. and Mulholland, A. J. (2010) Inclusion of dispersion effects significantly improves accuracy of calculated reaction barriers for cytochrome P450 catalyzed reactions. J. Phys. Chem. Lett. 1, 3232-3237. (48) Lonsdale, R., Harvey, J. N. and Mulholland, A. J. (2012) Effects of dispersion in density functional based quantum mechanical/molecular mechanical calculations on cytochrome P450 catalyzed reactions. J. Chem. Theory Comput. 8, 4637-4645. (49) Rydberg, P., Lonsdale, R., Harvey, J. N., Mulholland, A. J. and Olsen, L. (2014) Trends in predicted chemoselectivity of cytochrome P450 oxidation: B3LYP barrier heights for epoxidation and hydroxylation reactions. J. Mol. Graph. Model. 52, 30-35. (50) Altun, A., Breidung, J. r., Neese, F. and Thiel, W. (2014) Correlated Ab Initio and Density Functional Studies on H2 Activation by FeO+. J. Chem. Theory Comput. 10, 3807-3820. (51) Tomasi, J. and Persico, M. (1994) Molecular interactions in solution: an overview of


Page 20 of 28

Page 21 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


methods based on continuous distributions of the solvent. Chem. Rev. 94, 2027-2094. (52) Fu, Z., Wang, Y., Wang, Z., Xie, H. and Chen, J. (2015) Transformation pathways of isomeric perfluorooctanesulfonate precursors catalyzed by the active species of P450 enzymes: in silico investigation. Chem. Res. Toxicol. 28, 482-489. (53) Zhang, J., Ji, L. and Liu, W. (2015) In silico prediction of cytochrome P450-mediated biotransformations of xenobiotics: a case study of epoxidation. Chem. Res. Toxicol. 28, 1522-1531. (54) Rao, F., Chen, Z., Zhou, D., Kang, Y., Guo, L. and Xue, Y. (2018) DFT investigation on the metabolic mechanisms of theophylline by cytochrome P450 monooxygenase. J. Mol. Graph. Model. 84, 109-117. (55) Schöneboom, J. C. and Thiel, W. (2004) The resting state of P450cam: a QM/MM study. J. Phys. Chem. B 108, 7468-7478. (56) Wang, X., Chen, J., Wang, Y., Xie, H. and Fu, Z. (2015) Transformation pathways of MeO-PBDEs catalyzed by active center of P450 enzymes: a DFT investigation employing 6-MeO-BDE-47 as a case. Chemosphere 120, 631-636. (57) Preuss, R., Angerer, J. and Drexler, H. (2003) Naphthalene: an environmental and occupational toxicant. Int. Arch. Occup. Environ. Health 76, 556-576. (58) Gasteiger, J. and Marsili, M. (1980) Iterative partial equalization of orbital electronegativity—a rapid access to atomic charges. Tetrahedron 36, 3219-3228. (59) Wu, W., Wu, Z., Rong, C., Lu, T., Huang, Y. and Liu, S. (2015) Computational study of chemical reactivity using information-theoretic quantities from density functional reactivity theory for electrophilic aromatic substitution reactions. J. Phys. Chem. A 119, 8216-8224. (60) Wang, A., Savas, U., Stout, C. D. and Johnson, E. F. (2011) Structural characterization of the complex between α-naphthoflavone and human cytochrome P450 1B1. J. Biol. Chem. 286, 5736-5743. (61) Kumar, D., Karamzadeh, B., Sastry, G. N. and de Visser, S. P. (2010) What factors influence the rate constant of substrate epoxidation by compound I of cytochrome P450 and analogous iron (IV)-oxo oxidants? J. Am. Chem. Soc. 132, 7656-7667. (62) Chou, K. C. and Zhou, G. P. (1982) Role of the protein outside active site on the diffusion-controlled reaction of enzymes. J. Am. Chem. Soc. 104, 1409-1413. (63) Kuo-Chen, C. (1976) The kinetics of the combination reaction between enzyme and substrate. Sci. Sin. 19, 505-528. (64) Fukami, T., Katoh, M., Yamazaki, H., Yokoi, T. and Nakajima, M. (2008) Human cytochrome P450 2A13 efficiently metabolizes chemicals in air pollutants: naphthalene, styrene, and toluene. Chem. Res. Toxicol. 21, 720-725. (65) Halliwell, B. (1991) Reactive oxygen species in living systems: source, biochemistry, and role in human disease. Am. J. Med. 91, S14-S22. (66) Ray, P. D., Huang, B. W. and Tsuji, Y. (2012) Reactive oxygen species (ROS) homeostasis and redox regulation in cellular signaling. Cell. Signal. 24, 981-990. (67) Borosky, G. L. and Laali, K. K. (2007) Oxidized metabolites from benzo [a] pyrene, benzo [e] pyrene, and aza-benzo [a] pyrenes. A computational study of their carbocations formed by epoxide ring opening reactions. Org. Biomol. Chem. 5, 2234-2242. (68) Borosky, G. L. and Laali, K. K. (2010) Oxidized metabolites from cyclopenta-fused polycyclic aromatic hydrocarbons (CP-PAHs). A DFT model study of their carbocations



formed by epoxide ring opening. J. Phys. Org. Chem. 23, 810-818. (69) Shimada, T., Takenaka, S., Kakimoto, K., Murayama, N., Lim, Y.-R., Kim, D., Foroozesh, M. K., Yamazaki, H., Guengerich, F. P. and Komori, M. (2016) Structure-Function Studies of Naphthalene, Phenanthrene, Biphenyl, and Their Derivatives in Interaction with and Oxidation by Cytochromes P450 2A13 and 2A6. Chem. Res. Toxicol. 29, 1029-1040. (70) Yang, Z., Doubleday, C. and Houk, K. N. (2015) QM/MM protocol for direct molecular dynamics of chemical reactions in solution: The water-accelerated Diels-Alder reaction. J. Chem. Theory Comput. 11, 5606-5612. (71) Yang, Z., Yang, S., Yu, P., Li, Y., Doubleday, C., Park, J., Patel, A., Jeon, B., Russell, W. K. and Liu, H. (2018) Influence of water and enzyme SpnF on the dynamics and energetics of the ambimodal [6+4]/[4+2] cycloaddition. Proc. Natl. Acad. Sci. U. S. A., 115, E848–E855. (72) Roos, P. H. and Bolt, H. M. (2005) Cytochrome P450 interactions in human cancers: new aspects considering CYP1B1. Expert Opin. Drug Metab. Toxicol. 1, 187-202. (73) Hall, E. A., Sarkar, M. R. and Bell, S. G. (2017) The selective oxidation of substituted aromatic hydrocarbons and the observation of uncoupling via redox cycling during naphthalene oxidation by the CYP101B1 system. Catal. Sci. Technol. 7, 1537-1548. (74) Cho, T. M., Rose, R. L. and Hodgson, E. (2006) In vitro metabolism of naphthalene by human liver microsomal cytochrome P450 enzymes. Drug Metab. Dispos. 34, 176-183. (75) Shimada, T., Kim, D., Murayama, N., Tanaka, K., Takenaka, S., Nagy, L. D., Folkman, L. M., Foroozesh, M. K., Komori, M. and Yamazaki, H. (2013) Binding of diverse environmental chemicals with human cytochromes P450 2A13, 2A6, and 1B1 and enzyme inhibition. Chem. Res. Toxicol. 26, 517-528. (76) Shimada, T., Murayama, N., Tanaka, K., Takenaka, S., Imai, Y., Hopkins, N. E., Foroozesh, M. K., Alworth, W. L., Yamazaki, H. and Guengerich, F. P. (2008) Interaction of polycyclic aromatic hydrocarbons with human cytochrome P450 1B1 in inhibiting catalytic activity. Chem. Res. Toxicol. 21, 2313-2323. (77) Shimada, T., Tanaka, K., Takenaka, S., Foroozesh, M. K., Murayama, N., Yamazaki, H., Guengerich, F. P. and Komori, M. (2009) Reverse Type I Binding Spectra of Human Cytochrome P450 1B1 Induced by Flavonoid, Stilbene, Pyrene, Naphthalene, Phenanthrene, and Biphenyl Derivatives That Inhibit Catalytic Activity: A Structure-Function Relationship Study. Chem. Res. Toxicol. 22, 1325-1333.


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Figure and Table Captions

Figure 1. The area of within 5 Å of naphthalene (Nap) of the snapshot 10 ns, containing amino acid residues Gly, Ala, Phe, Ile, Leu, Thr, Val, Asp. The unit for bond distances is Å.



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Table 1. Activation barrier, Selected QM/MM bond distance and bond angle in the Reactant (R) in the total 15 snapshots of Rate-determining Step in the Process of Activation. Attack to C4 Time(ns)

Distance

Attack to C3 Angle

Barriers(kcal·mol-1)

Distance

Angle

(O-C3, Å)

(Fe-O-C3, º)

Barriers(kcal·mol-1) (O-C4, Å)

(Fe-O-C4, º)

2

21.4

3.31

152.2

11.6

3.00

130.3

4

24.2

3.18

148.2

16.1

3.07

125.6

5

27.9

3.20

149.1

13.9

3.05

126.7

6

26.8

3.20

152.0

16.8

2.93

129.9

7

23.2

3.16

148.8

12.9

3.01

125.6

8

17.8

3.39

147.6

14.3

3.11

127.3

9

25.5

3.45

146.0

15.6

3.12

126.7

10

13.5

3.26

151.2

12.2

3.09

125.9

11

21.4

3.45

146.9

13.4

3.12

127.7

12

26.4

3.49

147.0

12.2

3.19

127.6

13

19.9

3.58

147.6

13.0

3.10

131.7

14

23.5

3.42

146.4

12.6

3.03

128.0

15

24.1

3.57

145.8

11.5

3.16

128.8

16

23.0

3.60

148.9

13.0

2.87

128.1

18

27.9

3.31

148.8

14.9

2.98

129.5


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Figure 2. a, b, Distributions of distance (O-C4, Å) and distance (O-C3, Å), angle (Fe-O-C4, º) and angle (Fe-O-C3, º) during 20ns MD simulation of the CYP 1A1-naphthalene complex, representing by hollow dots, and solid square points represent distributions after QM/MM geometry optimization of the total 15 snapshots. c, d, Correlations of angle (Fe-O-C3, º) and distance (O-C3, Å), angle (Fe-O-C4, º) and distance (O-C4, Å) during 20ns MD simulation, representing by hollow dots, and solid square points represent correlations after QM/MM geometry optimization and are graded of neutral gray to obtained activation barrier.



Figure 3. Optimized structures of reactant (R), transition state (TS), Intermediate (IM), transition state of epoxidation (TSEPO), product of epoxidation (PEPO) involved in the two offensive approaches of QM region of the system at snapshot 10 ns. The black number represents atomic distance, and the red number represents NPA charge. The unit of atomic distance is Å.


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Scheme 1. The epoxidation strategies of naphthalene after the O atom of Cpd I bond with the C atom of the naphthalene

Figure 4. Potential energy profiles of doublet spin for the formation of epoxidation production from initiating reactants. All values are in kcal∙mol-1 relative to the reactants.



Figure 5. Potential energy profiles for the ring-opening of naphthalene 1,2-oxide production by hydroxyl radical and hydronium ion.


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Carcinogenic Metabolic Activation Process of Naphthalene by the

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