Extremophile

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== Extraordinary Proteins ==
== Extraordinary Proteins ==
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== Where there is no man, be a bacteria ==
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Life - DNA, Proteins, physiology, behavior, and all - has managed to weather extreme environments - almost every hole we've poked a stick into contains thriving living communities. Proteins are a necessity for living, and therefore guarding - or more accurately put, "tuning" - their structures to an extreme environment is of paramount value to an evolving organism seeking an extraordinary niche. In this article we'll present the biophysical strategies apparent from some extreme protein structures.
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Where no man or plant could survive, bacteria have been eking out a living, and some even thriving. From the Dead Sea which has 10 times the concentration of salt in salt sea water to the hot springs heated by the molten center of the earth, that pour forth through vents deep under the sea (see this fantastic [http://www.bbc.co.uk/nature/adaptations/Thermophile#p004htvq Thermophile Video] from BBC Wildlife) - in all these hostile environments, life has found footing. To make the question stronger, realize that many things can go wrong, cells could burst or shrivel, DNA can become undone and tattered, protein can unfold into a jumbled mass of amino acids, and membranes made of fat molecules can rip and melt. Environment stress usually achieves all or many of these deadly process to organisms - yet some bacteria survive. To study how the extremophiles (extreme-loving bacteria) survive involves explaining how each of the above processes that should kill the bacteria, in fact do not occur. To understand all of these is a tall order, but to start, in this Proteopedia article, we'll tackle the protein survival under extreme stress problem.
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== Extremophiles talk in thermodynamics terms ==
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== Salty condition can be overcome with extra Negative surface charge density ==
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All stresses must be interpreted into the language of thermodynamics, since that is the most faithful representation of the problems the environment brings to proteins, and the way the structures have solved this problem, and found a way to maintain their stability.
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The principle equation is:<br />
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The green alga Dunaliella salina lives in an environment where salt levels change swiftly and dramatically from low to high salt concentrations. The problem for its extra-cellular proteins is staying soluble in both solvents. Professors Sussman and Zamir from the Weizmann Institute report the first such protein crystal structure and suggest that the protein's relative increase of negative surface charge density turns the protein into a anion-like molecule capable of dissolving in high salt. However, unlike the halophilic enzyme from Haloarcula marismortui which Profs. Sussman and Maverach (Tel Aviv University) crystallized earlier, the negative surface charge is not so high that the protein becomes insoluble in lower salt concentrations. The three-way comparison between the salt-adapting properties of a mesophilic, halotolerant, and halophilic enzyme illuminates a biophysical strategy for tuning protein structures to extreme salt conditions.
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::<big>∆G = ∆H - T∆S</big>.<br />
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Where ∆G is negative, the movement to products in the reaction is spontaneous. This means, for the case of going from unfolded protein to folded protein as the product, a negative ∆G wold correspond to a stable protein structure. The other three terms: ∆H, T, and ∆S correspond to the change in enthalpy, the temperature (in Kalvins), and the change in entropy. Where the product is more stable than the reactants, ∆H will be negative, and the products are more ordered than the reactant, ∆S will be negative. It can be seen from the equation that ∆G becomes more negative for a more negative ∆H or for a less negative ∆S.
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== Negative surface charge and solubility ==
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In salty water, most proteins aggregate. That proteins on the outside of some archea in the dead sea manage to remain soluble in solutions entering up to one salt molecule for every two H20 molecules is quite stunning. Over a decade's work, Joel Sussman, Ada Zamir, and others at Weizmann Institute and Tel Aviv University have shown that the negative density on the surface of proteins turn them into anion-like, hence soluble in salt-containing solutions. The more recent research involved halotolerant organisms's halotolerant enzymes, and showing that their intermediate negative surface charge enables them to walk the tightrope between little salt and salf-saturating conditions, repectively. Still mysterious, though, is why all halophilic proteins aren't for the same price halotolerant - what use is all that extra negative surface charge?
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We next look at a thermophilic enzyme, also solved by Weizmann Institute lab - Professor Yigal Burstein and his team of scientists.
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In the panel below, the increasing negative charge density on the surface is apparent. Notice also that while the halotolerant enzyme (center) switches positive amino acids to neutral, the halophilic enzyme (right), also switches neutral amino acids to become negative. In a nutshell, the problem of salty condition includes the problem of how to remain soluble; the general solution is to become anion-like through increasing the negative charge surface density; and the molecular implementation is through decreasing the relative amount of positively charged amino acids and/or increasing the relative amount of negatively charged amino acids.
* <scene name='JMS/sandbox7/1raz/2'>"Regular enzyme" with least negative charge</scene> [[1raz]]
* <scene name='JMS/sandbox7/1raz/2'>"Regular enzyme" with least negative charge</scene> [[1raz]]

Revision as of 15:41, 25 April 2013

halophilic enzyme (PDB entry 1hlp)

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