Calorimetric observation of a GroEL-protein binding reaction with little contribution of hydrophobic interaction.
Binding of Escherichia coli chaperonin, GroEL, to substrate proteins with non-native structure, reduced alpha-lactalbumin (rLA) and denatured pepsin, were analyzed by isothermal titration calorimetry at various temperatures in the presence of salt (0.2 M KCl). Both proteins bound to GroEL with 1:1 stoichiometry and micromolar affinity at all temperatures tested. However, thermodynamic properties of their binding to GroEL are remarkably different from each other. While heat capacity changes (DeltaCp) of rLA-GroEL binding showed large negative values, -4.19 kJ mol-1 K-1, that of denatured pepsin-GroEL binding was only -0.2 kJ mol-1 K-1. These values strongly indicate that the hydrophobic interaction is a major force of rLA-GroEL binding but not so for denatured pepsin-GroEL binding. When salt was omitted from the solution, the affinity and DeltaCp of the rLA-GroEL binding reaction were not significantly changed whereas denatured pepsin lost affinity to GroEL. Thus, in the non-native protein-GroEL binding reaction, thermodynamic properties, as well as the effect of salt, differ from protein to protein and hydrophobic interaction may not always be a major driving force.
Aoki
K
K
Tokyo Institute of Technology, Research Laboratory of Resources Utilization, R-1, 4259 Nagatsuta, Yokohama 226, Japan.
Taguchi
H
H
Shindo
Y
Y
Yoshida
M
M
Ogasahara
K
K
Yutani
K
K
Tanaka
N
N
D002151:Calorimetry / Q000379:methods; D018834:Chaperonin 60 / Q000737:chemistry / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D004926:Escherichia coli / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D011485:Protein Binding; D013816:Thermodynamics
D018834:Chaperonin 60