The GroEL/GroES chaperonin ring machine

The GroEL/GroES chaperonin machine provides ATP-mediated kinetic assistance to folding to the native state of a large number of substrate proteins. In ongoing studies, we have been addressing the nature of the action of ATP, the trigger to the activation of folding, employing cryoEM studies of an ATP hydrolysis-defective (D398A) version of GroEL. An apparent sequence of conformational states has been observed that chart a trajectory of movements that are associated with polypeptide binding (to early states) followed by potential stretching (by a later-formed one), the last-formed state poised for docking of the cochaperonin ring, GroES. Because polypeptide remains bound to the apical domains at the point of such docking, this ensures that it does not escape during the encapsulation process. The step of GroES docking is followed by further large rigid body apical domain movements that eject substrate protein from the cavity wall into the domed chamber where folding ensues. We have continued to investigate whether the electrostatically rich chamber wall takes an active vs. passive role in the folding process.