Structural basis of allosteric changes in the GroEL mutant Arg197Ala

Helen E. White¹, Shaoxia Chen¹, Alan M. Roseman¹, Ofer Yifrach², Amnon Horovitz² and Helen R. Saibil^1
1Crystallography Department, Birkbeck College, Malet St, London WC1E 7HX UK. ²Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100 Israel.

Explanation	Thumbnail Image	Standard Animation	Alternate Animation
This sequence shows the movements of the apical domains (top and bottom layers of the double-ring structure) directly from the side. The seven-fold axis of symmetry is in the vertical direction. Extension and twisting of the apical domains leads to progressive opening of the rings, and the inter-ring contacts also appear to weaken, as shown by the gaps appearing between adjacent subunits.	Side View	Quick Time Movie	Animated GIF
The same sequence is shown with the oligomer tipped forward by 45 degrees, to allow a view into the upper cavity. The apical domains can take up a wide range of conformations by rotations about hinge regions in the GroEL subunit.	Top View	Quick Time Movie	Animated GIF
The sequence is shown with the oligomer tipped backward 45 degrees, showing the lower cavity. The T ring of the asymmetric TR state (50 µM ATP) has a particularly twisted conformation, and the side view (movie 1) shows it to be closed.	Bottom View	Quick Time Movie	Animated GIF

These movies show the succession of conformational changes induced by ATP binding to the GroEL mutant Arg197Ala. Each frame is a surface-rendered view of a 3D reconstruction from electron cryomicroscopy, starting with wild-type GroEL for comparison. The sequence is wild type GroEL, R197A GroEL, R197A-50 µM ATP, R197A-100 µM ATP, R197A-2.5 mM ATP. Without ATP, both rings are in the T (tense) allosteric state, at 2.5 mM ATP, both are in the R (relaxed) state, and at 50 µM ATP, the upper ring is in the R state and the lower ring is in the T state.