SDS-induced conformational changes and inactivation of the bacterial chaperonin GroEL

The inactivation and conformational changes of the bacterial chaperonin Gro EL have been studied in SDS solutions with different concentrations. The re sults show that increasing the SDS concentration caused the intrinsic fluor escence emission intensity to increase and the emission peak to slightly bl ue-shift, indicating that increasing the SDS concentration can cause the hy drophobic surface to be slightly buried. The changes in the ANS-binding flu orescence with increasing SDS concentration also showed that the GroEL hydr ophobic surface decreased. At low SDS concentrations, less than 0.3 mM, the GroEL ATPase activity increased with increasing SDS concentration. Increas ing the SDS concentration beyond 0.3 mM caused the GroEL ATPase activity to quickly decrease. At high SDS concentrations, above 0.8 mM, the residual G roEL ATPase activity was less than 10% of the original activity, but the Gr oEL molecule maintained its native conformation las indicated by the exposu re of buried thiol groups, electrophoresis, and changes of CD spectra). The above results suggest that the conformational changes of the active site r esult in the inactivation of the ATPase even though the GroEL molecule does not markedly unfold at low SDS concentrations.