Toward the Physical Basis of Thermophilic Proteins: Linking of Enriched Polar Interactions and Reduced Heat Capacity of Unfolding

AbstractThe enrichment of salt bridges and hydrogen bonding in thermophilic proteins has long been recognized. Another tendency, featuring lower heat capacity of unfolding (ΔCp) than found in mesophilic proteins, is emerging from the recent literature. Here we present a simple electrostatic model to illustrate that formation of a salt-bridge or hydrogen-bonding network around an ionized group in the folded state leads to increased folding stability and decreased ΔCp. We thus suggest that the reduced ΔCp of thermophilic proteins could partly be attributed to enriched polar interactions. A reduced ΔCp might serve as an indicator for the contribution of polar interactions to folding stability