Heat capacity-independent determination of differential free energy of stability between structurally homologous proteins.
Under the assumption of equivalent heat capacity values, the differential free energy of stability for a pair of proteins midway between their thermal unfolding transition temperatures is shown to be independent of DeltaC(p) up to its cubic term in DeltaT(m). For model calculations reflecting the nearly 30 degrees C difference in T(m) for the adenylate kinases from the arctic bacterium Bacillus globisporus and the thermophilic bacterium Geobacillus stearothermophilus, the resultant error in estimating DeltaDeltaG by the formula 0.5 [DeltaS(T(m1))(1)+DeltaS(T(m2)) (2)] DeltaT(m) is less than 1%. Combined with the analogous thermal unfolding data for the adenylate kinase from Escherichia coli, these three homologous proteins exhibit T(m) and DeltaS(T(m)) values consistent with differential entropy and enthalpy contributions of equal magnitude. When entropy-enthalpy compensation holds for the differential free energy of stability, the incremental changes in T(m) values are shown to be proportionate to the changes in free energy.
Lemaster
David M
DM
Wadsworth Center, New York State Department of Health and Department of Biomedical Sciences, University at Albany-SUNY, Empire State Plaza, Albany, New York 12201-0509, USA.
D000263:Adenylate Kinase / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry*; D003901:Desulfovibrio / Q000201:enzymology; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology; D008954:Models, Biological; D011489:Protein Denaturation; D017510:Protein Folding; D013816:Thermodynamics; D016963:Thermus thermophilus / Q000201:enzymology
D001426:Bacterial Proteins; D000263:Adenylate Kinase