Microbiology/Genetics

Why Humans Have Lighter or Darker Skin Color?

The NCKX5 ion exchanger

By Stefan Anitei, Science Editor

27th of February 2008, 19:06 GMT

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It is simplistic to differentiate people in races based on the skin tones. What we call Blacks can be separated in many races, equally or not related between them and other races; the term White is misleading too. In the case of the so-called Mongoloid race, skin tones vary significantly.

But no matter what, skin color is one of the most visible factors

that helps differentiate human look, and a new research adds to explain us the variety of skin tones in humans.

A 2005 study had detected a gene called SLC24A5 to be involved in determining skin color. The team led by Rebecca Ginger from the Unilever Corporate Research, Bedfordshire, UK, has now showed that the protein encoded by this gene, called NCKX5, is an ion exchanger, in a research published in the JBC Online. This molecule exchanges sodium for calcium through a membrane, regulated by potassium.

But this protein acts differently from other NCKX proteins: the NCKX5 is not located on the cell surface, but inside a cell structure called the trans-Golgi network. In the Golgi-network, new proteins and vesicles are synthesized, changed and sorted.
When the team shut off the activity of NCKX5 in melanocytes, the skin cells that synthesize the dark pigment called melanin, the melanin amounts plummeted. The researchers also discovered that the substitution of the amino acid alanine at position 111, in the molecule of the exchanger protein, with the amino acid threonine, as found in the case of the European allele (gene variant), was connected to lighter skin tone, due to decreased NCKX5's exchanger activity.

For the moment, the team can only suppose that NCKX5 could be crucially involved in the substance transporting that controls the activity of melanosomes, cell vesicles where melanin is synthesized. This way, the higher or lower NCKX5 effectiveness controls the total melanin production in melanocytes and the color of the skin.

TAGS:

human | skin | color | melanin | gene

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