Unraveling the Mechanism of Tyrosinase

Technion researchers have successfully captured the working mechanism of tyrosinase on the molecular level using X-ray crystallography, Nature Communications reported this week.

The two faculties responsible for catching tyrosinase “in the act” are the Faculty of Biotechnology and Food Engineering and the Schulich Faculty of Chemistry. The laboratory of Assoc. Prof. Ayelet Fishman from the Department of Biotechnology and Food Engineering primarily studies the correlation between the structure and function of enzymes. One of these enzymes is tyrosinase, which is ubiquitous in all domains of life and can be found in microorganisms, plants, and animals. It is responsible for the first two steps in the synthesis of the dark pigment melanin.

In humans tyrosinase is localized in melanocyte cells in the epidermis, and the formed melanin determines the color of skin, hair and eyes, but more importantly protects against the hazardous UV light. Mutations in this enzyme are the main cause for albinism, a condition that causes impaired vision and sensitivity to light. In fruits and vegetables tyrosinase initiates browning, which results in economic losses to farmers. Prof. Adir’s lab uses X-ray crystallography to obtain high resolution three dimensional structures of biological macromolecules.

tyrosineTyrosinase performs two successive oxidation reactions: conversion of small organic molecules (such as the amino acid tyrosine) to a di-phenol, and oxidation of the di-phenol to quinone, subsequently turning into melanin. The enzyme requires two copper ions, and the prevailing belief in the scientific community is that each activity is performed on a different copper ion.

Mor Goldfeder, a joint PhD student in both labs, and Dr. Rita Kanteev from Prof. Fishman’s lab solved the structure of a bacterial tyrosinase in the presence of two substrates: the monophenol tyrosine, and the di-phenol L-Dopa. Additionally, they managed to solve a structure with another substrate, in which the catalytic product was directly observed during its formation. These are the first visualizations of the enzyme during the catalytic cycle, showing that the enzyme was in its active form in the crystal. Sivan Isaschar-Ovdat, a PhD student studying applications of tyrosinase in foods, also participated in the research. The structures prove unequivocally that all of the substrates are stabilized in the same orientation at the active site of the enzyme, and are positioned towards the same copper ion.

Understanding of the mechanism and structure of tyrosinase can help in developing inhibitors for treatment of hyperpigmentation and age spots, improving the sensitivity of melanoma cells towards radiation therapy, and prevention of browning of fruits and vegetables.

In the photo – the tyrosinase team. from left to right – Assoc. Prof. Ayelet Fishman, Sivan Isaschar-Ovdat, Mor Goldfeder,  Dr. Rita Kanteev and Prof. Noam Adir