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 and elephants are both large animals that take life slow - walking slow, singing slow.. But whales swim underwater while holding their breaths for long periods of time, and elephants can not: Why can whales hold their breaths for long, and elephants can not? 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 extreme demand, and why can't elephants' myoglobin accumulate to high concentrations as well? In a recent article in the journal Science[1], the laboratories of Professors Berenbrink, Campbell, and Cossins demonstrate that natural variation in net positive charge explains aquatic and terrestrial animals' different diving abilities. Following this pattern, 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 charge[2], where a protein with a higher net charge is much more soluble.
It 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 +2: (summing up the total charge of the protein) , , , , , , , .
- 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[1]) - have a charge of about +0.5.
