LIGANDS REGULATE GROEL THERMOSTABILITY

Escherichia coli heat-shock proteins GroEL and GroES stimulate (in an ATP-dependent manner) the folding of various proteins. In this study s canning microcalorimetry was applied to investigate GroEL thermostabil ity in the presence of its ligands. Mg2+ and K+ ions stabilize while A DP destabilizes the GroEL molecule against the action of temperature. Furthermore, ADP essentially increases the number of binding sites for the hydrophobic probe (ANS) and the number of GroEL SH-groups accessi ble to Ellman's reagent as well as the accessibility of the protein to the action of trypsin. The interaction of GroEL with GroES in the pre sence of Mg2+-ADP eliminates the destabilizing effect of ADP on the Gr oEL molecule against the action of temperature and Ellman's reagent bu t does not change its hydrophobicity and accessibility to trypsin. (C) 1997 Federation of European Biochemical Societies.