The hydrophobic nature of GroEL-substrate binding.
The molecular chaperone GroEl from Escherichia coli is a member of the highly conserved Hsp60 family of proteins that facilitates protein folding. A central question regarding the mechanism of GroEL-assisted refolding of proteins concerns its broad substrate specificity. The nature of GroEL-polypeptide chain interaction was investigated by isothermal titration calorimetry using proteins that maintain a non-native conformation in neutral buffer solutions. A single molecule of an unfolded variant of subtilisin BPN' binds non-cooperatively to GroEL with micromolar affinity and a positive enthalpy change. Additional calorimetric titrations of this chain with GroEL show that the positive enthalpy change decreases with increasing temperature between 6 and 25 degrees C, yielding a delta CP of -0.85 kcal mol-1 degree-1. alpha-Casein similarly binds to GroEL with micromolar affinity and a positive enthalpy change in the range of 15-20 degrees C, yielding a delta CP of -0.44 kcal mol-1 degree-1. The negative heat capacity change provides strong evidence for the role of hydrophobic interactions as the driving force for the association of these substrates with the GroEL chaperonin.
Lin
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Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, Rockville.
Schwartz
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Eisenstein
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D000595:Amino Acid Sequence; D002151:Calorimetry; D018834:Chaperonin 60 / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D008969:Molecular Sequence Data; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013379:Substrate Specificity; D013381:Subtilisins / Q000378:metabolism
D018834:Chaperonin 60; D013381:Subtilisins