The structural differences between mushroom and human tyrosinase cleared by investigating the inhibitory activities of stilbenes

Abstract

Tyrosinase (TYR: EC 1.14.18.1) is a copper-containing protein that catalyzes phenolic oxidation. The enzyme plays a critical role in melanin production and is widely distributed from microorganisms to humans. To date, many kinds of TYR inhibitors have been discovered for medical, cosmetic, and agricultural uses. In various TYRs, mushroom (Agaricus bisporus) tyrosinase (AbTYR) is widely used to search for inhibitors of TYRs because the enzyme is easy to handle and cheaper than other sources. However, some inhibitors behave in different ways for hTYR and AbTYR because the two enzymes share only about 23% of their sequences. Therefore, it is important to reveal the difference in the structure of the active pocket of both TYRs. To date, naturally-derived inhibitors, such as stilbenes, flavonoids, and coumarins, have been preferred for the ingredients of cosmetics and food preservatives. In this study, we compared the inhibitory activities of 6 stilbenes for Ab and hTYR. The A ring of these stilbenes has a 3,5-dihydroxy or dimethoxy group and the B ring of these stilbenes has several patterns in position and number of hydroxyl group, including no hydroxylation. As a result, compounds that did not have an active hydroxyl group in the A ring were not effective for AbTYR but effective for hTYR. The absence of hydroxyl groups in the B ring made the inhibitory activity weak for hTYR but effective for AbTYR. These results indicate that the A and B rings on stilbene can only enter into the active pocket of the AbTYR and hTYR, respectively. These results were then supported by the molecular docking of oxyresveratrol, which is the most potent inhibitor of Ab and hTYR (IC50 = 3.0 and 0.7, respectively). Molecular docking also revealed that the common feature and difference in the active pocket in the two enzymes. These results exploit the importance of the selection of biological resources according to the objective use.