Eukaryotic chaperonin CCT stabilizes actin and tubulin folding intermediates in open quasi-native conformations

Abstract

Three‐dimensional reconstruction from cryoelectron micrographs of the eukaryotic cytosolic chaperonin CCT complexed to tubulin shows that CCT interacts with tubulin (both the α and β isoforms) using five specific CCT subunits. The CCT–tubulin interaction has a different geometry to the CCT–actin interaction, and a mixture of shared and unique CCT subunits is used in binding the two substrates. Docking of the atomic structures of both actin and tubulin to their CCT‐bound conformation suggests a common mode of chaperonin–substrate interaction. CCT stabilizes quasi‐native structures in both proteins that are open through their domain‐connecting hinge regions, suggesting a novel mechanism and function of CCT in assisted protein folding.