Extraordinary Proteins
The living have managed to colonize extraordinary environments. Without proteins, living doesn't happen. "Extreme" proteins demonstrate many intriguing biophysical features enabling their function in harsh environments.
Well-tuned negative surface charge density enables solubility in a broad range of salt conditions
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, from D. salina, 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. Too little negative charge and the enzyme can only tolerate low salt conditions, too much negative charge and the enzyme can only stand high salt conditions, but in moderation, the right amount of negative charge enables an enzyme to remain soluble in both low and high salt conditoins.
In the list below, notice how the negative surface charge density is lowest for the mesophilic, highest for the halophilic, and in intermediate for the halotolerant enzyme. negative, positive, and neutral amino acids are colored red, blue and white, respectively:
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℃.
Professors Yigal Burstein (Weizmann Institute) and Felix Frolow (Tel Aviv University) studied a (1ykf) from T. brockii that maintains its structure in over 83℃.
They 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.
