Superoxide dismutase (SOD, EC 220.127.116.11) plays an important antioxidant defense role in skins exposed to oxygen. We studied the inhibitory effects of Al3+ on the activity and conformation of manganese-containing SOD (Mn-SOD). Mn-SOD was significantly inactivated by Al3+ in a dose-dependent manner. The kinetic studies showed that Al3+ inactivated Mn-SOD follows the first-order reaction. Al3+ increased the degree of secondary structure of Mn-SOD and also disrupted the tertiary structure of Mn-SOD, which directly resulted in enzyme inactivation. We further simulated the docking between Mn-SOD and Al3+ (binding energy for Dock 6.3: ？14.07？kcal/mol) and suggested that ASP152 and GLU157 residues were predicted to interact with Al3+, which are not located in the Mn-contained active site. Our results provide insight into the inactivation of Mn-SOD during unfolding in the presence of Al3+ and allow us to describe a ligand binding via inhibition kinetics combined with the computational prediction. 1. Introduction Superoxide dismutases (SOD, EC 18.104.22.168) are a class of enzymes that catalyze the dismutation of superoxide into oxygen and hydrogen peroxide [1–3]. They play an important antioxidant defense role in skins exposed to oxygen. In this regard, for the treatment of systemic inflammatory diseases including skin ulcer lesions, the topical application of free Mn-SOD or Cu, Zn-SOD extracted from bovine, bacterial, and other species was dramatically effective in skin lesions . It has been reported that significant increase in the levels of SOD occurs in vitiligo patients due to the increased oxidative stress . The involvement of oxidative stress in chronic idiopathic urticaria associated with SOD was also reported : the activity of SOD was markedly increased in lesional skin as compared with skin of healthy subjects, indicating that oxidative stress is crucially involved in chronic idiopathic urticaria and suggesting that oxidative stress is secondary to the development of inflammation. The earlier reports [7, 8] suggested that the activity of activator protein-1, which is associated with tumor promotion, was reduced in Mn-SOD transgenic mice overexpressing Mn-SOD in the skin, suggesting that Mn-SOD reduced tumor incidence by suppressing activator protein-1 activation. The mechanism of Mn-SOD catalysis is very important, and the mechanism therefore needs to be investigated from different sources using various kinetic methods. The information regarding the tertiary structure and the structural integrity of the active site of Mn-SOD is little known and in
P. V. Sravani, N. K. Babu, K. V. T. Gopal et al., “Determination of oxidative stress in vitiligo by measuring superoxide dismutase and catalase levels in vitiliginous and non-vitiliginous skin,” Indian Journal of Dermatology, Venereology and Leprology, vol. 75, no. 3, pp. 268–271, 2009.
G. Raho, N. Cassano, V. D'Argento, G. A. Vena, and F. Zanotti, “Over-expression of mn-superoxide dismutase as a marker of oxidative stress in lesional skin of chronic idiopathic urticaria,” Clinical and Experimental Dermatology, vol. 28, no. 3, pp. 318–320, 2003.
Y. Zhao, Y. Xue, T. D. Oberley et al., “Overexpression of manganese superoxide dismutase suppresses tumor formation by modulation of activator protein-1 signaling in a multistage skin carcinogenesis model,” Cancer Research, vol. 61, no. 16, pp. 6082–6088, 2001.
Y. Zhao, T. D. Oberley, L. Chaiswing et al., “Manganese superoxide dismutase deficiency enhances cell turnover via tumor promoter-induced alterations in AP-1 and p53-mediated pathways in a skin cancer model,” Oncogene, vol. 21, no. 24, pp. 3836–3846, 2002.
S. Marklund and G. Marklund, “Involvement of the superoxide anion radical in the autoxidation of pyrogallol and a convenient assay for superoxide dismutase,” European Journal of Biochemistry, vol. 47, no. 3, pp. 469–474, 1974.
D. T. Moustakas, P. T. Lang, S. Pegg et al., “Development and validation of a modular, extensible docking program: DOCK 5,” Journal of Computer-Aided Molecular Design, vol. 20, no. 10-11, pp. 601–619, 2006.
D. Krewski, R. A. Yokel, E. Nieboer et al., “Human health risk assessment for aluminium, aluminium oxide, and aluminium hydroxide,” Journal of Toxicology and Environmental Health. Part B, vol. 10, supplement 1, pp. 1–269, 2007.
L. G. Parkinson, N. L. Giles, K. F. Adcroft, M. W. Fear, F. M. Wood, and G. E. Poinern, “The potential of nanoporous anodic aluminium oxide membranes to influence skin wound repair,” Tissue Engineering. Part A, vol. 15, no. 12, pp. 3753–3763, 2009.
R. Anane, “Lipid peroxidation as pathway of aluminium cytotoxicity in human skin fibroblast cultures: prevention by superoxide dismutase+catalase and vitamins E and C,” Human and Experimental Toxicology, vol. 20, no. 9, pp. 477–481, 2001.
M. I. Yousef, “Aluminium-induced changes in hemato-biochemical parameters, lipid peroxidation and enzyme activities of male rabbits: protective role of ascorbic acid,” Toxicology, vol. 199, no. 1, pp. 47–57, 2004.
D. Orihuela, V. Meichtry, N. Pregi, and M. Pizarro, “Short-term oral exposure to aluminium decreases glutathione intestinal levels and changes enzyme activities involved in its metabolism,” Journal of Inorganic Biochemistry, vol. 99, no. 9, pp. 1871–1878, 2005.