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Salt of the Earth - From Israel's Sea

November 10, 2005
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The Dead Sea: Clues to a breakthrough?
Life thrives in all sorts of hostile environments, including the extreme salinity of the Dead Sea. A team of scientists has uncovered a strategy that helps a plant-like, microscopic alga to happily proliferate in such inhospitable surroundings - and their findings have unexpectedly shed light on the working of human kidneys.

Over the years, a number of Weizmann Institute scientists have addressed the question of how molecules essential to life, such as proteins, have adapted to function in extreme environments.

The proteins they investigated were isolated from halophilic (salt-loving) micro-organisms from the Dead Sea. After determining the 3-D structures for several halophilic proteins, researchers were able to explain how these proteins not only cope with high salinities, but are actually "addicted" to them.

However, the alga Dunaliella salina is an organism of a different streak: It is able to grow in any salinity, from the extremes of the Dead Sea to nearly fresh water.

The uniquely salt-tolerant Dunaliella, which is commercially grown as a source of natural beta carotene, has been investigated at the Weismann Institute for 30 years. Yet the secrets of its exceptionally successful adaptation to salt remained unresolved.

In a recently published paper in the Proceedings of the National Academy of Sciences, USA (PNAS) Institute scientists professor Ada Zamir and Dr. Lakshmanane Premkumar of the institute's biological chemistry department, and professor Joel Sussman and Dr. Harry Greenblatt of the structural body department revealed the structural basis of a remarkably salt-tolerant Dunaliella enzyme, a carbonic anhydrase, which may hold the key.

Comparisons with known carbon anhydrases from animal sources showed that the Dunaliella enzyme shares a basic plan with its distant relatives, but with a few obvious differences.

The most striking of these is in the electrical charges on the proteins' surfaces: Charges on the salt-tolerant enzyme are uniformly negative, while the surfaces of carbonic anhydrases that don't tolerate salt sport a negative/positive/neutral mix.

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