JMS/sandbox9

Extraordinary Proteins

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.

Salty conditions can be overcome with extra negative surface charge density

The green alga Dunaliella salina lives in the Dead Sea of Israel where water currents can change its environment swiftly and dramatically from low to high salt concentrations (see an interesting Scientific American article about life in the Dead Sea [1]). The problem for its proteins is staying soluble in both solvents. In 2005, Professors Sussman and Zamir from the Weizmann Institute reported the first crystal structure for a halotolerant protein - a (1y7w) - 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 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.

In the list below, the increasing negative charge density on the surface is apparent. Notice also that while the halotolerant enzyme only switches positive amino acids to neutral, the halophilic enzyme also switches neutral amino acids to become negative.

• 1raz
• 1y7w
• 1ldm
• 1hlp

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.

High temperatures encourage using proline to lower entropy loss and between-chain ion-network bonding to increase enthalpy gain

Some bacteria and even animals can survive great temperatures. Eggs fry - meaning their proteins denature, at 65℃. But Thermoanearobacter brockii, discovered in Yellowstone Park, continues to grow in 80℃, and makes an (1ykf) that maintains its structure in over 83℃. Professors Yigal Burstein (Weizmann Institute) and Felix Frolow (Tel Aviv University) identified two contributing factors to this enzymes thermal prowess. 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. 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. There is therefore a smaller loss of entropy upon folding into the native structure.