Temperature Dependence of the Stability of Ion Pair Interactions, and its Implications on the Thermostability of Proteins from Thermophiles

Abstract

An understanding of the determinants of the thermal stability of thermostable proteins is expected to enable design of enzymes that can be employed in industrial biocatalytic processes carried out at high temperatures. A major factor that has been proposed to stabilize thermostable proteins is the high occurrence of salt bridges. The current study employs free energy calculations to elucidate the thermodynamics of the formation of salt bridge interactions and the temperature dependence, using acetate and methylguanidium ions as model systems. Three different orientations of the methylguanidinium approaching the carboxylate group have been considered for obtaining the free energy profiles. The association of the two ions becomes more favorable with an increase in temperature. The desolvation penalty corresponding to the association of the ion pair is the lowest at high temperatures. The occurrence of bridging water molecules between the ions ensures that the ions are not fully desolvated, and this could provide an explanation for the existence of internal water molecules in thermostable proteins reported recently. The findings provide a detailed picture of the interactions that make ion pair association at high temperatures a favorable process, and reaffirm the importance of salt bridges in the design of thermostable proteins.

Temperature, Hydrostatic Pressure, and Osmolyte Effects on Liquid–Liquid Phase Separation in Protein Condensates: Physical Chemistry and Biological Implications

“…For example, explicit-water simulated PMFs of acetate andm ethylguanidinium indicateamild strengthening of the favorable contact interaction from T = 300 to 400 K. Desolvation barriers are observed in these PMFs as well. [181] The presence of these desolvation barriers and solvent-separated minimas imilar to those in Figure 10 af or hydrophobic interactions suggestst hat considerations of void volumes, p-dependence, and low-volume solventseparated configurations similar to those for hydrophobic interactions could apply to p-related and charge-charge interactions as well. To gain further insights into the physical basis of (T,p)-dependent biomolecular LLPS, future efforts should be directed towarde lucidatingt he T-a nd p-dependence of these interactions.…”

“…Even for the PMFs for a pair of amino acids carrying charges of the same sign, a desolvation barrier is seen in both PMFs in Figure c, and a low but nonetheless discernible desolvation barrier is present in each of the PMFs in Figure d. Temperature dependences of PMFs of amino acid analogues have been investigated to a limited degree in the literature. For example, explicit‐water simulated PMFs of acetate and methylguanidinium indicate a mild strengthening of the favorable contact interaction from T =300 to 400 K. Desolvation barriers are observed in these PMFs as well . The presence of these desolvation barriers and solvent‐separated minima similar to those in Figure a for hydrophobic interactions suggests that considerations of void volumes, p ‐dependence, and low‐volume solvent‐separated configurations similar to those for hydrophobic interactions could apply to π‐related and charge–charge interactions as well.…”

Current Status of Mining, Modification, and Application of Cellulases in Bioactive Substance Extraction

“…Flexible regions are usually located at the Nand C-terminal ends of a protein, or in the random coil structure. Several studies have shown that salt bridges play an essential role in protein thermal stability and that the numbers of bridges are positively related to thermostability [54]. During protein synthesis, post-translational modifications are crucial, and different modification processes will have different effects on proteins.…”

Active sites and thermostability of a non-specific nuclease fromYersinia enterocoliticasubsp. palearcticaby site-directed mutagenesis

“…Their results showed that the pair-wise interaction energies for the saltbridges E6/R92 and E62/K46 were stabilizing and insensitive to temperature changes from 298 to 348 K. They suggest that the extra salt-bridges found in thermophilic proteins enhance the thermostability of proteins by reducing ᭝C p , leading to the up-shifting and broadening of the protein stability curves [36,37]. Based on a large body of research on the relationship between thermostability and salt bridges [38][39][40][41][42][43], salt bridges must be closely related to protein thermostability. Higher thermostability tends to be associated with more salt bridges in proteins.…”