Extremophile

Our first example comes from the algae Dunaliella salina, found growing on the shores of the dea sea by Prof. Volcani, working at the Experimental Research Station (now the Volcani Institute), and then housed on the campus of the Daniel Sieff Institute (now the Weizmann Institute). Appropriately, scientist from the Weizmann Institute, Prof Joel Sussman, Dr. Adi Zamir and collegues, crystallized the that hangs out of the membrane of D. salina. Now, living on the shore of the Dead Sea presents a special problem for the living. While the dead sea is a challenge with its enormous concentration of salt, living on its shores means one must cope with high salt concentrations, but also - normal salt concentrations. That is, the adaptations to high salt must leave open the possibility of living with normal salt concentrations, too. After comparing the enzyme found on shore dwelling bacteria - appropriately named halo-tolerant (able to withstand high and normal salt concentrations) with enzymes from normal bacteria and purely halophilic ones (some bacteria can even live inside a salt crystal!), they noticed a particular feature of a the protein's structure which was associated with halotolerance. There were - particularly Lysine - on its surface compared to the amount found in the normal enzymes. And unlike the halophilic enzymes, which also had more negatively-charged amino acids, the halotolerant enzyme had a normal number of negatively charged amino acids. Apparently, this intermediate structural property enables the halotolerant enzyme to walk the tightrope, balancing adaptation for high and for medium salt concentrations. Because the thermodynamic threat of salt is not well understood, and nor is the role of increasing the negative surface charge, I label the thermodynamic definition of the structural adaptation ambiguously by not specifying whether it is enthalpic or entropic:

= .

In the next example, however, I specify the thermodynamic terms which a structural adaptation personifies. For that, we turn to a thermophilic enzyme, also solved by Weizmann Institute lab - Porfessor Yigal Burstein and his team of scientists.

Some bacteria and even animals can survive great temperatures. Studying , Prof. Burstein noticed two special features that appear to explain this enzymes ability to maintain its structure in over 83℃! For comparison, you could fry an egg at 65℃, which mean all the protein in an egg denature at significantly less than 83℃. To demonstrate the special structural properties of the thermophilic enzyme underlies its thermophilic prowess, Prof Burstein selectively altered normal enzymes to have the two structural features, and indeed found that the normal enzymes had become thermophilic. The two properties relate to ∆H and to ∆S. Firstly, he found the thermophilic enzyme had a unique that encompassed two monomers of the tetrameric enzyme, repeating between each monomer and its two partner monomers. This network apparently makes the oligomer more stable, or ∆H more negative. Secondly, the thermophilic enzyme was . Because proline's side chain has minimal degree of freedom, proline's, unlike other amino acids, are minimally restricted by folding. Therefore, ∆S is less negative. These two structural properties are labelled by the corresponding term in the thermodynamics equation:

= - T.