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. The problem for its proteins is staying soluble in both solvents.

In 2005, Scientists from the Weizmann Institute reported the first crystal structure for the first halotolerant enzyme, a - a (1y7w), having solved in 1995 (together with scientists from Tel Aviv University) the structure of the first halophilic enzyme, a (1hlp) from Haloarcula marismortui.

They conclude that a general solution for remaining soluble in salty conditions it to become "anion-like" through increasing the negative charge surface density. In the list below, notice how the negative surface charge density increases from the mesophiles, to the halotolerant, and to the halophilic enzyme. Also notice how in the halotolerant enzyme only the the number of positively charged amino acids is less than its mesophilic homologue, but the halophilic enzyme additionally has more negatively charged amino acids than its mesophilic homologue.

• 1raz with "normal" amount of positively- and negatively-charged regions
• 1y7w with less positively-charged regions but normal amount of positively-charged regions
• 1ldm with "normal" amount of positively- and negatively-charged regions
• 1hlp with less positively-charged regions and more positively-charged regions

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 a (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.