Catalase and superoxide dismutase response and the underlying molecular mechanism for naphthalene.

Naphthalene, a naturally-occurring polyaromatic hydrocarbon, pose potential threats to health for its wide exposures in environment. Naphthalene could disrupt the redox equilibrium resulting in oxidative damage. Antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) are considered to be the efficient defense barriers to protect organisms from negative impacts of toxicants. Limited information is available regarding the underlying molecular mechanism between antioxidant enzymes and naphthalene. In this paper, structural and functional alterations of CAT and SOD for low dose (1.6-25.6 mg/L) naphthalene exposure have been investigated at the molecular and cellular levels. The enzyme activity responses of CAT and SOD in hepatocytes for naphthalene were consistent with the molecular, in which the activity of CAT increased and the activity of SOD slightly inhibited. Spectroscopy methods and molecular docking were carried out to investigate the underlying binding mechanisms. Naphthalene exposure significantly changed the conformation of CAT with secondary structure alteration (α-helix increase) but only changed the skeleton structure of SOD without secondary structure alteration. Naphthalene could bind to CAT and SOD primarily via H-binding force accompanied with the particle size of CAT/SOD agglomerates decreasing. Naphthalene preferentially bound to the surface of CAT and SOD. Besides, naphthalene could also bind directly to the active center of CAT with the key residues Arg364 and Tyr 357 for activity. This paper provides a combined cellular and molecular strategy to research biomarker responses for toxicants exposure. Besides, this study offers detailed basic data for the comprehensive understanding of naphthalene toxicity.