Extremophile

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 tuning protein 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.

Positively charged myoglobin allows whales to hold their breaths during long dives

Whales dive and sail the seas, making heroic planetary circles. But elephants, while astonishing in their tight family structures and appreciation of mourning, cannot hold their breaths long. One clue to this discrepancy is the difference in concentrations of in whale and elephant muscle tissue: More myoglobin means more oxygen storage capacity, and whales have over 15 times the concentration of myoglobin as elephants do (70 mg/g wet mass compared to the elephants 4.6). But this leads to a biophysical question.

A very high concentration of myoglobin should lead to aggregation, which would prevent myoglobin from functioning, so how do whales' myoglobin deal with this extraordinary demand, and why can't elephants' myoglobin accumulate to such high concentrations as well? In a fascinating article^[1], Professor Micheal Berenbrink, Professor Andrew Cossins and colleagues demonstrate that whale myoglobin has a net charge two formal charges higher than in elephants: +4 compared to +2 in the elephant. Apparently a protein's solubility is a function of its net surface charge, where a protein with a higher net charge is much more soluble.

It all comes down to . Without these amino acids, myoglobin in both whale and elephants has a charge of +1. Calculate along the chain, in the N to C-terminal direction how just several amino acid switches bring the positive net charge of whale myoglobin up to +4 and elephants to only +2: , , , , , , , .

• Asp and Glu have a charge of -1, Arg and Lys have a charge of +1, His in the positions shown here - 12 and 116 (Table S2) - have a charge of about +0.5.

Fascinating as this single example is, most intriguingly the authors show how this divergence in net positive charge explains the different diving abilities of aquatic versus terrestrial animals across the animal kingdom!