An electrostatic basis for the stability of thermophilic proteins

Abstract

Two factors provide key contributions to the stability of thermophilic proteins relative to their mesophilic homologues: electrostatic interactions of charged residues in the folded state and the dielectric response of the folded protein. The dielectric response for proteins in a "thermophilic series" globally modulates the thermal stability of its members, with the calculated dielectric constant for the protein increasing from mesophiles to hyperthermophiles. This variability results from differences in the distribution of charged residues on the surface of the protein, in agreement with structural and genetic observations. Furthermore, the contribution of electrostatic interactions to the stability of the folded state is more favorable for thermophilic proteins than for their mesophilic homologues. This leads to the conclusion that electrostatic interactions play an important role in determining the stability of proteins at high temperatures. The interplay between electrostatic interactions and dielectric response also provides further rationalization for the enhanced stability of thermophilic proteins with respect to cold-denaturation. Taken together, the distribution of charged residues and their fluctuations have been shown to be factors in modulating protein stability over the entire range of biologically relevant temperatures.

Physics and evolution of thermophilic adaptation

“…Here, all stabilizing structural factors act in concert, pointing to enhanced compactness as the most probable original cause for higher stability. In the second case, on the contrary, we found a strong sequence bias that can explain dominating role of some of the stabilizing interactions, e.g., electrostatics (19,20), but not of others. The high level of sequence variation compared with mesophilic orthologs and the significant bias toward charged residues in their sequences point to a key role of sequence selection in adaptation of T. maritima proteins (1TMY and 1VJW) to extreme conditions of the environment, in contrast to other (hyper)thermophilic proteins (1CAA, 1IQZ, 2CJN, and 2PRD) where structural bias is more pronounced.…”

“…3 and Table 5), in turn, uncovers another possible mechanism of thermostability in T. maritima's proteins. The stability of these proteins under extremely high temperatures is apparently provided by significant modifications of their sequences toward enrichment by charged residues (19,20), which can be an effective sequence-based method of adaptation to extreme specific conditions. van der Waals interactions (29), number of H-bonds (12,30), and number of residues involved into elements of secondary structure in groups of proteins under consideration.…”

“…The increase of the number of charged residues in hyperthermophilic proteomes appears to be much greater than would have been necessary for stability purposes alone. Indeed, enhanced stability can be achieved by the addition of only a few ion pairs (4,19,20). This points to the possibility of alternative reasons (unrelated to protein stabilization) for this specific compositional bias toward charged residues, which should be thoroughly explored.…”

“…1a) and structural analysis (Table 1), it points to compactness as a key factor in the structure-based strategy of thermophilic adaptation in archaea. At the same time, lower packing density in proteins from A. aeolicus and T. maritima and a higher (compared with mesophilic E. coli, as well as with hyperthermophilic P. furiosus) content of charged residues suggest that these organisms follow mostly sequence-based stabilization, possibly, with a key role of ionic interactions (19,20).…”

Role of Internal Water on Protein Thermal Stability: The Case of Homologous G Domains

“…Moreover, the stabilizing contribution of salt-bridges partially buried in the protein matrix depends on the local polarity 5,13,14 while the presence of internal water molecules could alleviate the associated desolvation penalty 15,16 . In this regard, it was proposed that (hyper)thermophiles could benefit from dense ion-pairing because of a higher internal dielectric constant 17 . Finally, the presence of water molecules inside internal cavities or superficial pockets also improves the molecular packing and extends the HB connectivity with potential effects on local kinetic stability 18 .…”