title: Thermodynamic differences among homologous thermophilic and mesophilic proteins.
abstract: Here, we analyze the thermodynamic parameters and their correlations in families containing homologous thermophilic and mesophilic proteins which show reversible two-state folding <--> unfolding transitions between the native and the denatured states. For the proteins in these families, the melting temperatures correlate with the maximal protein stability change (between the native and the denatured states) as well as with the enthalpic and entropic changes at the melting temperature. In contrast, the heat capacity change is uncorrelated with the melting temperature. These and additional results illustrate that higher melting temperatures are largely obtained via an upshift and broadening of the protein stability curves. Both thermophilic and mesophilic proteins are maximally stable around room temperature. However, the maximal stabilities of thermophilic proteins are considerably greater than those of their mesophilic homologues. At the living temperatures of their respective source organisms, homologous thermophilic and mesophilic proteins have similar stabilities. The protein stability at the living temperature of the source organism does not correlate with the living temperature of the protein. We tie thermodynamic observations to microscopics via the hydrophobic effect and a two-state model of the water structure. We conclude that, to achieve higher stability and greater resistance to high and low temperatures, specific interactions, particularly electrostatic, should be engineered into the protein. The effect of these specific interactions is largely reflected in an increased enthalpy change at the melting temperature.
authors.affiliation: Laboratory of Experimental and Computational Biology and Intramural Research Support Program-SAIC, Laboratory of Experimental and Computational Biology, National Cancer Institute-Frederick, Building 469, Room 151, Frederick, Maryland 21702, USA.
authors.forename: S
authors.initials: S
authors.lastname: Kumar
authors.forename: C J
authors.initials: CJ
authors.lastname: Tsai
authors.forename: R
authors.initials: R
authors.lastname: Nussinov
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000737:chemistry; D000220:Adaptation, Biological; D019843:Archaeal Proteins / Q000737:chemistry; D002480:Cellulase / Q000737:chemistry; D004795:Enzyme Stability; D006360:Heat-Shock Proteins / Q000737:chemistry; D006358:Hot Temperature; D008962:Models, Theoretical; D011489:Protein Denaturation; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry*; D012260:Ribonucleases / Q000737:chemistry; D013816:Thermodynamics; D018909:src Homology Domains; D000097024:Acylphosphatase
chemical_list: D017766:Acid Anhydride Hydrolases; D019843:Archaeal Proteins; D002480:Cellulase; D006360:Heat-Shock Proteins; D011506:Proteins; D012260:Ribonucleases; D000097024:Acylphosphatase