Health and Medicine

The Secret Behind Melanin Formation Unraveled

melanin

The color of the human hair and skin is determined by the pigment “melanin”, which can also be found in nearly every living thing.

Melanin helps in the repair of damaged tissues, and also aids insects in their defense against the impacts of disease-causing microbes. The presence of melanin is also exhibited in some fruits such as bananas in the form of dark spots. Nevertheless, melanin was still somewhat poorly understood, as the processes associated with the production of melanin were yet to be grasped completely.

Courtesy of an ingenious biotechnological technique, researchers at universities in Kiel and Mainz have been able to unmask the fundamental molecular mechanism involved in the formation of melanin. As a result of this, a significant lacuna in our hitherto understanding of the workings of this enzyme has been sufficiently filled. The action of the enzyme tyrosinase was discovered to be at the root of the workings of the molecular mechanism. This finding will usher in a new era in the evolution of several uses to which melanin can be put in various industries including food, medicine, cosmetics and environmental technology.

tyrosinase
Catalytic center of a tyrosinase: The two amino acids Glu235 and Asn240 bind to a water molecule HOH112, which strips a proton (white) away from the substrate (p-tyrosol). The resulting phenolate can then bind to the copper ion (CuA), starting the tyrosinase reaction. (Image credits: Institute of Molecular Biophysics, JGU)

The process of melanin formation is activated by tyrosinase. Heinz Decker from Johannes Gutenberg University Mainz (JGU) stated that beforehand, the role which tyrosinase played was not completely grasped, adding that they were more knowledgeable about the action of catechol oxidase, a less powerful relative of tyrosinase that was implicated in the formation of melanin. The reason behind the variation in the reactivity of catechol oxidase and tyrosinase has been the subject of several researches undertaken in the past couple decades, but unfortunately, these have recorded only limited positive results up till now.

Taking a pointer from the documented findings of an Israeli research team with Dr. A. Fishman as its leader, the team of Professor Felix Tuczek of Kiel University, and Professor Heinz Decker and Even Solem of Mainz University, made the decision to carry out experiments using a biotechnological technique that involved targeted mutation with the aim of unraveling the mechanism behind the activity of tyrosinase. Using the aforementioned technique, catechol oxidase was initially isolated from the wine leaves of Riesling and then transmuted to tyrosinase. They then discovered that a couple of amino acids; asparagine and glutamic acid (which was greatly conserved), found at close-range to the catalytic center were responsible for the variation in reactivity between tyrosinase and catechol oxidase. A particular water molecule had a powerful bond with these two amino acids inside the protein arrangement that caused the water molecule to experience a charge displacement. This was responsible for one end possessing a strong negative charge, and as a result removing a proton from an adjoining monophenol. This event triggers the tyrosinase, which then transforms the monophenols into quinones; which are chemical substances that have great reactivity. Melanin is then formed through the independent combination of quinones. Without the presence of either a molecule of water within the protein or asparagine, there wouldn’t be tyrosinase present, rather catechol oxidase alone would be present.

This finding constitutes a groundbreaking achievement in the quest to fully grasp the function of tyrosinase as a catalyst in the formation of melanin. This leaves open the possibility of making advancements in the processes of inhibition, modification and stimulation, and also in the biotechnological techniques utilized in environmental research, medicine, and the manufacture of cosmetics, through the aid of research focused mainly in the study of genetics.

The full study was published in Angewandte Chemie International journal.

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