Reversible thermal transition in GrpE, the nucleotide exchange factor of the DnaK heat-shock system

DnaK, a Hsp70 acting in concert with its co chaperones DnaJ and GrpE, is es sential for Escherichia coli to survive environmental stress, including exp osure to elevated temperatures. Here we explored the influence of temperatu re on the structure of the individual components and the functional propert ies of the chaperone system. GrpE undergoes extensive but fully reversible conformational changes in the physiologically relevant temperature range (t ransition midpoint at similar to 48 degreesC), as observed with both circul ar dichroism measurements and differential scanning calorimetry, whereas no thermal transitions occur in DnaK and DnaJ between 15 degreesC and 48 degr eesC. The conformational changes in GrpE appear to be important in controll ing the interconversion of T-state DnaK (ATP-liganded, low affinity for pol ypeptide substrates) and R-state DnaK (ADP-liganded, high affinity for poly peptide substrates). The rate of the T --> R conversion of DnaK due to DnaJ triggered ATP hydrolysis follows an Arrhenius temperature dependence. In c ontrast, the rate of the R --> T conversion due to GrpE catalyzed ADP/ATP e xchange increases progressively less with increasing temperature and even d ecreases at temperatures above similar to 40 degreesC, indicating a tempera ture-dependent reversible inactivation of GrpE. At heat-shock temperatures, the reversible structural changes of GrpE thus shift DnaK toward its high- affinity R state.