Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Formation of the browning pigment melanin decoded

04.07.2016

Researchers in Mainz and Kiel have uncovered the molecular mechanism behind the synthesis of melanin using a technique involving mutation of the relevant enzyme tyrosinase

Melanin is a pigment which is present in almost all life forms and that determines hair and skin color in humans. It helps insects protect themselves against the effects of pathogenic microorganisms and it promotes tissue repair. The dark spots on fruits such as bananas can be attributed to the presence of melanin.


View into the 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 now bind to the copper ion (CuA), starting the tyrosinase reaction.

Image/©: Institute of Molecular Biophysics

However, the processes involved in the formation of this pigment were not yet fully understood. Researchers at the universities in Mainz and Kiel have now uncovered the molecular mechanism underlying melanin synthesis using a clever biotechnological procedure. With this, a major gap in our understanding of how this enzyme functions has been closed.

At the core of the mechanism is the activity of the enzyme tyrosinase. This discovery opens the door to the development of numerous applications in the cosmetics and food industries as well as in environmental technology and medicine.

Tyrosinase initiates the melanin synthesis process. "We previously did not fully understand the role played by this enzyme. In fact, we knew more about the activities of catechol oxidase, a related but less potent enzyme that is also involved in the synthesis of melanin," explained Heinz Decker, Director of the Institute of Molecular Biophysics at Johannes Gutenberg University Mainz (JGU).

Much research on the cause for the difference in the reactivity of tyrosinase and catechol oxidase has been conducted over the past few decades, but little success had been achieved to date.

Following up on clues from reported research undertaken by an Israeli team led by Dr. A. Fishman, Professor Heinz Decker and Even Solem of Mainz University and Professor Felix Tuczek of Kiel University decided to conduct experiments to discover the mechanism responsible for tyrosinase activity. They first isolated a catechol oxidase from Riesling wine leaves and converted it to a tyrosinase by means of a biotechnological process involving targeted mutation.

They found that the difference in reactivity is attributable to two amino acids, a highly conserved glutamic acid and asparagine that are located near the catalytic center. They form such a strong bond with a specific water molecule within the protein matrix that the water molecule undergoes a charge displacement.

This makes one side strongly negative, so that it strips a positive proton from a nearby monophenol. This then activates tyrosinase which converts the monophenols to chemically very reactive substances called quinones, which combine on their own to form melanin. However, in the absence of asparagine or a water molecule in the protein, only catechol oxidase is present and no tyrosinase.

This discovery is a major breakthrough in the understanding of the catalytic role played by tyrosinase in the synthesis of melanin. This means that in the future it will be possible to make systematic improvements in the processes of stimulation, inhibition, and modification as well as in biotechnological methods employed in medicine, cosmetics production, and in environmental research, with the help of genetically-based approaches.

"In addition, we have gained further insights into the functioning of copper in the body," concluded Decker. The results of the study have been published in the journal Angewandte Chemie International Edition.

Publication:
Even Solem, Felix Tuczek, Heinz Decker
Tyrosinase versus Catechol Oxidase: One Asparagine Makes the Difference
Angewandte Chemie International Edition, 15 January 2016
DOI: 10.1002/anie.201508534

Image:
http://www.uni-mainz.de/bilder_presse/10_biophysik_tyrosinase.jpg
View into the 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 now bind to the copper ion (CuA), starting the tyrosinase reaction.
Image/©: Institute of Molecular Biophysics

Further information:
Professor Dr. Heinz Decker
Institute of Molecular Biophysics
Johannes Gutenberg University Mainz
55099 Mainz, GERMANY
phone +49 6131 39-23570
fax +49 6131 39-23557
e-mail: hdecker@uni-mainz.de
http://www.biophysik.uni-mainz.de/

Weitere Informationen:

http://onlinelibrary.wiley.com/wol1/doi/10.1002/anie.201508534/full

Petra Giegerich | idw - Informationsdienst Wissenschaft

More articles from Life Sciences:

nachricht Hunting pathogens at full force
22.03.2017 | Helmholtz-Zentrum für Infektionsforschung

nachricht A 155 carat diamond with 92 mm diameter
22.03.2017 | Universität Augsburg

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Pulverizing electronic waste is green, clean -- and cold

22.03.2017 | Materials Sciences

Astronomers hazard a ride in a 'drifting carousel' to understand pulsating stars

22.03.2017 | Physics and Astronomy

New gel-like coating beefs up the performance of lithium-sulfur batteries

22.03.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>