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Int. J. Mol. Sci. 2010, 11(11), 4506-4510; doi:10.3390/ijms11114506

Article
Insight into the Strong Antioxidant Activity of Deinoxanthin, a Unique Carotenoid in Deinococcus Radiodurans
Hong-Fang Ji
Shandong Provincial Research Center for Bioinformatic Engineering and Technique, Shandong University of Technology, Zibo 255049, China; E-Mail: jhf@sdut.edu.cn; Tel.:+86-533-278-0271; Fax: +86-533-278-0271
Received: 23 October 2010; in revised form: 3 November 2010 / Accepted: 7 November 2010 /
Published: 10 November 2010

Abstract

: Deinoxanthin (DX) is a unique carotenoid synthesized by Deinococcus radiodurans, one of the most radioresistant organisms known. In comparison with other carotenoids, DX was proven to exhibit significantly stronger reactive oxygen species (ROS)-scavenging activity, which plays an important role in the radioresistance of D. radiodurans. In this work, to gain deeper insights into the strong antioxidant activity of DX, the parameters characterizing ROS-scavenging potential were calculated by means of quantum chemical calculations. It was found that DX possesses lower lowest triplet excitation energy for its unique structure than other carotenoids, such as β-carotene and zeaxanthin, which endows DX strong potential in the energy transfer-based ROS-scavenging process. Moreover, the H-atom donating potential of DX is similar to zeaxanthin according to the theoretical homolytic O-H bond dissociation enthalpy. Thus, the large number of conjugated double bonds should be crucial for its strong antioxidant activity.
Keywords:
deinoxanthin; lowest triplet excitation energy; bond dissociation enthalpy; density functional theory

1. Introduction

Deinococcus radiodurans is a red-pigmented, nonphotosynthetic bacterium well known for its resistance to ionizing radiation [13]. It has been demonstrated that cellular antioxidants make important contributions to the radioresistance of D. radiodurans besides the efficient and accurate DNA repair strategy [4,5]. Among nonenzymic antioxidants, carotenoids possess efficient reactive oxygen species (ROS) scavenging capacity [6]. It is interesting to note that D. radiodurans synthesizes a unique ketocarotenoid, deinoxanthin (DX, Figure 1), as its major carotenoid [79]. DX was proven to exhibit significantly stronger ROS scavenging ability than other known carotenoids, such as β-carotene (BC, Figure 1) and zeaxanthin (ZX, Figure 1) [9], and the strong antioxidant effect of DX plays an important role in the radioresistance of D. radiodurans [9]. Therefore, it is interesting to explore the mechanistic underpinnings underlying the higher antioxidant potential of DX relative to other carotenoids. In the present work, by means of quantum chemical calculations, the parameters to characterize the antioxidant potential of DX, including the lowest triplet excitation energy (ET1) and homolytic O-H bond dissociation enthalpy (BDE), were estimated. The theoretical results further our understanding of the higher ROS-scavenging activities of DX compared to BC and ZX.

2. Calculation Methods

The structures of DX, BC and ZX were fully optimized by hybrid density functional theory (DFT) [10,11] and B3LYP [1214] functional with 6–31G(d) Gaussian basis set. The nature of the stationary point was ascertained by performing harmonic frequency calculations. The lowest triplet state energies (ET1s) of DX, BC and ZX were calculated by time-dependent DFT (TD-DFT) formalism [1517] with the same basis set. To ensure the accuracy of the results, the O-H BDEs of DX and ZX were estimated using a combined method labeled as (RO)B3LYP/6-311+G(2d,2p)//AM1/AM1, which takes advantage of accuracy and economy [1821]. As the hydroxyls of DX and ZX are not conjugated with the polyene chain, which should influence little on the O-H bond dissociation reactions, only one double bond in the polyene chain is reserved while the rest was replaced by a methyl when estimating the O-H BDEs of DX and ZX. The two hydroxyl groups of ZX are equivalent and only one is considered. The O-H BDE was estimated according to the following equation, O-H BDE = Hr + HhHp [1821], in which, Hr is the enthalpy of radical generated through H-abstraction reaction, Hh is the enthalpy of H-atom, −0.49765 hartree, and Hp is the enthalpy of parent molecule.

All calculations were performed using Gaussian 03 package of programs [22].

3. Results and Discussion

Carotenoids are efficient singlet oxygen (1O2) quenchers. Owing to the rather low ET1 of carotenoids, 1O2 can be quenched through energy transfer (Equation 1); generating triplet excited state carotenoids and ground state oxygen (3O2).

Car ( S 0 ) + 1 O 2 Car ( T 1 ) + 3 O 2

The 1O2 quenching capability is a good indicator of the ET1. Table 1 lists the TD-B3LYP/6-31G(d) estimated ET1 of DX, BC and ZX. The theoretically predicted ET1s of BC and ZX are close to the experimental value [23,24], which verifies the methodology.

The ET1s of the three carotenoids are lower than the deactivation energy of 1O2 (0.97 eV), which indicates that they are 1O2 quenchers. Moreover, the ET1 of DX is approximately 0.1 eV lower relative to those of BC and ZX. The lower ET1 of DX will make the energy transfer process more favorable energetically, relative to the other two carotenoids, which is consistent with the experimental finding that DX possesses stronger 1O2 quenching ability than BC and ZX [9]. Moreover, it was reported that the 1O2 quenching enhanced as the number of conjugated double bonds in the polyene chain of carotenoids increased, by examining various naturally occurring carotenoids [25]. Thus, it can be inferred that the higher 1O2 quenching ability of DX than that of other carotenoids should mainly arise from its extended conjugated double bonds system.

The direct H-atom transfer is one of the most important radical-scavenging processes [1821]. Taking RO· as an example, the direct H-atom transfer process can be represented as follows.

CarOH  +  RO    CarO   +  ROH

Among the three carotenoids, DX and ZX possess hydroxyls as potential H-atom donors in their structures. O-H BDE acts as an appropriate parameter to characterize the H-atom donating ability [1821]. The O-H BDE of the hydroxyl in the six-membered ring of DX is calculated to be about 101.92 kcal/mol, and that of the butyl hydroxyl at the end of the polyene chain is about 104.71 kcal/mol. This indicates that on thermodynamic grounds the hydroxyl in the six-membered ring should play a predominant role in the H-atom transfer-based ROS scavenging processes of DX. Moreover, the theoretical O-H BDE of ZX is about 101.74 kcal/mol. The close O-H BDEs between DX and ZX imply that they possess similar H-atom donating potential thermodynamically.

Collectively, the extended conjugated double bonds system of DX seems crucial for its strong ROS-scavenging activity. The larger number of conjugated double bonds means DX possesses lower ET1, and thus higher 1O2 quenching potential through energy transfer, in comparison with BC and ZX. The strong ROS scavenging ability of DX renders this unique carotenoid great potential in antioxidant therapy application.

This work was supported in part by the National Natural Science Foundation of China (Grant No.30700113).

References

  1. Daly, MJ; Minton, KW. Interchromosomal recombination in the extremely radioresistant bacterium Deinococcus radiodurans. J. Bacteriol 1995, 177, 5495–5505. [Google Scholar]
  2. Cox, MM; Battista, JR. Deinococcus radiodurans—the consummate survivor. Nat. Rev. Microbiol 2005, 3, 882–892. [Google Scholar]
  3. Slade, D; Lindner, AB; Paul, G; Radman, M. Recombination and replication in DNA repair of heavily irradiated Deinococcus radiodurans. Cell 2009, 136, 1044–1055. [Google Scholar]
  4. Ghosal, D; Omelchenko, MV; Gaidamakova, EK; Matrosova, VY; Vasilenko, A; Venkateswaran, A; Zhai, M; Kostandarithes, HM; Brim, H; Makarova, KS; Wackett, LP; Fredrickson, JK; Daly, MJ. How radiation kills cells: survival of Deinococcus radiodurans and Shewanella oneidensis under oxidative stress. FEMS Microbiol. Rev 2005, 29, 361–375. [Google Scholar]
  5. Markillie, LM; Varnum, SM; Hradecky, P; Wong, K. Targeted mutagenesis by duplication insertion in the radioresistant bacterium Deinococcus radiodurans: radiation sensitivities of catalase (katA) and superoxide dismutase (sodA) mutants. J. Bacteriol 1999, 181, 666–669. [Google Scholar]
  6. Paiva, SA; Russell, RM. Beta-carotene and other carotenoids as antioxidants. J. Am. Coll. Nutr 1999, 18, 426–433. [Google Scholar]
  7. Lemee, L; Peuchant, E; Clerc, M; Brunner, M; Pfander, H. Deinoxanthin: A new carotenoid isolated from Deinococcus radiodurans. Tetrahedron 1997, 53, 919–926. [Google Scholar]
  8. Saito, T; Ohyama, Y; Ide, H; Ohta, S; Yamamoto, O. A carotenoid pigment of the radioresistant bacterium Deinococcus radiodurans. Microbios 1998, 95, 79–90. [Google Scholar]
  9. Tian, B; Xu, Z; Sun, Z; Lin, J; Hua, Y. Evaluation of the antioxidant effects of carotenoids from Deinococcus radiodurans through targeted mutagenesis, chemiluminescence, and DNA damage analyses. Biochim. Biophys. Acta 2007, 1770, 902–911. [Google Scholar]
  10. Hohenberg, P; Kohn, W. Inhomogeneous electron gas. Phys. Rev 1964, 136, B864–B871. [Google Scholar]
  11. Kohn, W; Sham, LJ. Self-consistent equations including exchange and correlation effects. Phys. Rev 1965, 140, A1133–A1138. [Google Scholar]
  12. Lee, C; Yang, W; Parr, RG. Development of the Colle-Salvetti correlation energy formula into a functional of the electron density. Phys. Rev. B 1988, 37, 785–789. [Google Scholar]
  13. Becke, AD. A new mixing of Hartree-Fock and local density-functional theories. J. Chem. Phys 1993, 98, 1372–1377. [Google Scholar]
  14. Stephens, PJ; Devlin, FJ; Chabalowski, CF; Frisch, MJ. Ab Initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields. J. Phys. Chem 1994, 98, 11623–11627. [Google Scholar]
  15. Stratmann, RE; Scuseria, GE; Frisch, MJ. An efficient implementation of time-dependent density-functional theory for the calculation of excitation energies of large molecules. J. Chem. Phys 1998, 109, 8218–8224. [Google Scholar]
  16. Bauernschmitt, R; Ahlrichs, R. Treatment of electronic excitations within the adiabatic approximation of time dependent density functional theory. Chem. Phys. Lett 1996, 256, 454–464. [Google Scholar]
  17. Casida, ME; Jamorski, C; Casida, KC; Salahub, DR. Molecular excitation energies to high-lying bound states from time-dependent density-functional response theory: characterization and correction of the time-dependent local density approximation ionization threshold. J. Chem. Phys 1998, 108, 4439–4449. [Google Scholar]
  18. Zhang, HY. Structure-activity relationships and rational design strategies for radical-scavenging antioxidants. Curr. Comput. Aided Drug Des 2005, 1, 257–273. [Google Scholar]
  19. Wright, JS; Johnson, ER; DiLabio, GA. Predicting the activity of phenolic antioxidants: theoretical methods, analysis of substituent effects, and application to major families of antioxidants. J. Am. Chem. Soc 2001, 123, 1173–1183. [Google Scholar]
  20. Ji, HF; Zhang, HY; Shen, L. A theoretical elucidation of radical-scavenging power of cyanindin. Nat. Prod. Commun 2006, 1, 229–235. [Google Scholar]
  21. Ji, HF; Zhang, HY; Shen, L. Proton dissociation is important to understanding structure-activity relationships of gallic acid antioxidants. Bioorg. Med. Chem. Lett 2006, 16, 4095–4098. [Google Scholar]
  22. Frisch, MJ; Trucks, GW; Schlegel, HB; Scuseria, GE; Robb, MA; Cheeseman, JR; Montgomery, JA; Vreven, T; Kudin, KN; Burant, JC; Millam, JM; Iyengar, SS; Tomasi, J; Barone, V; Mennucci, B; Cossi, M; Scalmani, G; Rega, N; Petersson, GA; Nakatsuji, H; Hada, M; Ehara, M; Toyota, K; Fukuda, R; Hasegawa, J; Ishida, M; Nakajima, T; Honda, Y; Kitao, O; Nakai, H; Klene, M; Li, X; Knox, JE; Hratchian, HP; Cross, JB; Adamo, C; Jaramillo, J; Gomperts, R; Stratmann, RE; Yazyev, O; Austin, AJ; Cammi, R; Pomelli, C; Ochterski, JW; Ayala, PY; Morokuma, K; Voth, GA; Salvador, P; Dannenberg, JJ; Zakrzewski, VG; Dapprich, S; Daniels, AD; Strain, MC; Farkas, O; Malick, DK; Rabuck, AD; Raghavachari, K; Foresman, JB; Ortiz, JV; Cui, Q; Baboul, AG; Clifford, S; Cioslowski, J; Stefanov, BB; Liu, G; Liashenko, A; Piskorz, P; Komaromi, I; Martin, RL; Fox, DJ; Keith, T; Al-Laham, MA; Peng, CY; Nanayakkara, A; Challacombe, M; Gill, PMW; Johnson, B; Chen, W; Wong, MW; Gonzalez, C; Pople, JA. Gaussian 03; Gaussian, Inc: Pittsburgh, PA, USA, 2003. [Google Scholar]
  23. Haley, JL; Fitch, AN; Goyal, R; Lambert, C; Truscott, TG; Chacon, JN; Stirling, D; Schalch, W. The S1 and T1 energy levels of all-trans-.-carotene. J Chem Soc Chem Commun 1992, 1175–1176. [Google Scholar]
  24. Wang, C; Tauber, MJ. High-yield singlet fission in a zeaxanthin aggregate observed by picosecond resonance Raman spectroscopy. J. Am. Chem. Soc 2010, 132, 13988–13991. [Google Scholar]
  25. Hirayama, O; Nakamura, K; Hamada, S; Kobayasi, Y. Singlet oxygen quenching ability of naturally occurring carotenoids. Lipids 1994, 29, 149–150. [Google Scholar]
Ijms 11 04506f1 1024
Figure 1. Chemical structures of deinoxanthin, β-carotene and zeaxanthin.

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Figure 1. Chemical structures of deinoxanthin, β-carotene and zeaxanthin.
Ijms 11 04506f1 1024
Table Table 1. Theoretically estimated lowest triplet excitation energies (ET1) of deinoxanthin (DX), β-carotene (BC) and zeaxanthin (ZX) (in eV).

Click here to display table

Table 1. Theoretically estimated lowest triplet excitation energies (ET1) of deinoxanthin (DX), β-carotene (BC) and zeaxanthin (ZX) (in eV).
DXBCZX
Theoretical data0.690.800.80
Experimental data-0.88 [23]0.87 [24]
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