The alphabet of intrinsic disorder: II. Various roles of glutamic acid in ordered and intrinsically disordered proteins

Uversky, Vladimir N

High content of charged residues is one of the tricks used by Nature to make stable proteins in thermophilic and hyperthermophilic organisms. 132 In fact, based on the correspondence analysis of the 56 completely sequenced genomes available from the three domains of life (seven eukaryotes, 14 archaeal and 35 bacterial species) it has been concluded and the amino acid composition permits discrimination between the three known lifestyles (mesophily, thermophily or hyperthermophily). 132 The most specific amino acid compositional biases that represent specific signatures of thermophilic and hyperthermophilic proteomes are a relative abundance in glutamic acid, concomitantly with a depletion in glutamine and a significant correlation between the relative abundance in glutamic acid (negative charge) and the increase in the lumped "pool" lysine + arginine (positive charges). Being absent in mesophiles, these correlations could represent a physico-chemical basis of protein thermostability. Curiously, the distribution of the remaining charged amino acid, i.e., aspartic acid, appears to be quite homogeneous throughout all the species suggesting that this residue does not participate significantly in the aforementioned compensatory negative/positive (charged) correlation in thermophiles and hyperthermophiles. 132 On average, thermophilic and hyperthermophilic proteomes were shown to contain 1.9%, 7.8%, 4.8% and 12.6% of glutamine, glutamic acid, aspartic acid and lysine + arginine residues, respectively. Importantly, some of these numbers are rather different from those found in IDPs/IDPRs, as shown in Table 1 .