Effect And Mechanism Of Heavy Metal Cadmium On Tyrosinase

BackgroundCadmium ions(Cd2+)are a widespread and easily absorbed toxin to both humans and animals that can be spread via food,water,and air pollution.Cadmium ions do not have the known function in the human body,but they tend to lead to cumulative effects by long-term exposure to accumulation in the organism.At present,the discharge of wastewater from electroplating,mining and smelting is the main source of cadmium pollution.Cadmium wastewater,which is not treated strictly,is easy to enter the body through food and water,accumulating in the body for a long time,causing chronic poisoning of human body,causing toxic effects to the human body and seriously threatening human health.In the past reports,researchers have gaineda clear understanding of the mechanisms of cadmium toxicity in humans through epidemiological studies,in vivo and in vitro studies.The researchers confirmed that the toxic effects of cadmium on human body are mainly nephrotoxicity and bone toxicity.Besides,they also include liver toxicity,pulmonary toxicity,genotoxicity,gastrointestinal toxicity,neurotoxicity,carcinogenic toxicity and reproductive toxicity.Moreover,tzhe toxic effects and mechanisms of heavy metal cadmium on various biologic enzyme have also been studied by researchers,such as paraoxonase 1,alpha glucosidase,human uracil DNA glycosylase,alkaline phosphatase,acetylcholinesterase and antioxidant enzymes.However,the effect and mechanism of heavy metal cadmium on tyrosinase are not clear.Tyrosinase plays an important role in the formation of animal melanin,and is closely related to skin pigmentation disease.The effect and mechanism of two valent cadmium to tyrosinase can help to expand the understanding of the effect of heavy metal cadmium on the human body,and provide new theoretical support and direction for the study of tyrosinase related diseases.MethodWe evaluated the toxic effects of Cd2+ on tyrosinase activity and conformation by measuring kinetics and computationally simulating the interactions.The main contents of the study are as follows:(1)the inhibition and reversibility of Cd2+ on tyrosinase activity;(2)the inhibitory type of Cd2+ to tyrosinase activity;(3)the time process kinetics of the inhibition of tyrosinase activity by Cd2+;(4)whether Cd2+causes the change of the conformation of tyrosinase and the exposure of the surface hydrophobic group;(5)through molecular dynamics simulation and computer docking,we verified the conformational changes induced by Cd2+ and tyrosinase and the residues bound to tyrosinase active sites.ResultsThe results of the study show that Cd2+ to be a slope-hyperbolic noncompetitive-inhibition reversible inhibitor of tyrosinase,with an IC50 of 2.92 ±0.16 mM and Ki of 0.23 ± 0.02 mM.Spectrofluorimetric measurements of intrinsic and ANS-binding fluorescence showed that Cd2+ did not induce significant changes to tyrosinase overall or to its regional active site conformations.Cd2+ showed its inactivation effect not by modulating apparent structural changes to tyrosinase,but by occupying binding sites.To gain further insight into the Cd2+/tyrosinase interaction,we performed computational docking and molecular dynamics simulations.The results consistently indicated that Cd 2+ can interact with several residues near the tyrosinase active site,primarily HIS85 and ASN260.ConclusionHeavy metal cadmium has a significant inhibitory effect on tyrosinase,and its inhibition mechanism is a slope-hyperbolic noncompetitive-inhibition reversible way, which does not significantly change the three grade structure of tyrosinase,but can change the conformation of tyrosinase active pocket.Cd 2+ might inhibit tyrosinase activity by preventing L-DOPA from entering the active site pocket to the copper docking site.Our study provides insight into the mechanism of the toxic effects Cd2+.has on tyrosinase,which could provide new insights into the effects of cadmium on normal pigmentation pathway in animals,extended data on the inhibition of tyrosinase induced by cadmium,increasing the scientific understanding of the effect mechanism of cadmium.