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Sequential ATP-induced allosteric transitions of the cytoplasmic chaperonin containing TCP-1 revealed by EM analysis

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The eukaryotic cytoplasmic chaperonin containing TCP-1 (CCT) is a hetero-oligomeric complex that assists the folding of actins, tubulins and other proteins in an ATP-dependent manner. To understand the allosteric transitions that occur during the functional cycle of CCT, we imaged the chaperonin complex in the presence of different ATP concentrations. Labeling by monoclonal antibodies that bind specifically to the CCTα and CCTδ subunits enabled alignment of all the CCT subunits of a given type in different particles. The analysis shows that the apo state of CCT has considerable apparent conformational heterogeneity that decreases with increasing ATP concentration. In contrast with the concerted allosteric switch of GroEL, ATP-induced conformational changes in CCT are found to spread around the ring in a sequential fashion that may facilitate domain-by-domain substrate folding. The approach described here can be used to unravel the allosteric mechanisms of other ring-shaped molecular machines.

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Figure 1: Steps in the alignment of images of 8g antibody-bound CCT particles illustrated for apo CCT and particle classification.
Figure 2: Symmetry analysis of class averages of 8g monoclonal antibody-bound CCT particles in the presence of different concentrations of ATP.
Figure 3: Average power spectra of the rotational correlation plots corresponding to the class averages at different concentrations of ATP.
Figure 4: Difference maps between images at different concentrations of ATP indicating spread of ATP-induced conformational changes.

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Change history

  • 13 February 2005

    Sentences changed in Methods section


  1. *Note: In the version of this article originally published online, a mistake was introduced during the production process. This mistake occurs in the last paragraph before the Methods section. The correct first four sentences in this paragraph should read “Our results indicate two important differences between CCT and GroEL that probably have functional importance. First, considerable apparent conformational heterogeneity is seen in the apo state of CCT, but not in GroEL. This heterogeneity decreases with increasing ATP concentration and may reflect protein substrate specificity of different CCT subunits in the protein substrate acceptor state of CCT. Second, our results indicate that the ATP-induced conformational changes in CCT take place in a sequential manner according to the KNF model20, in contrast with the concerted mechanism observed in the case of GroEL.” This error has been corrected for the HTML and print versions of the article. We apologize for any inconvenience this may have caused.


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This work was supported by The Israel Science Foundation. D.R.-S is a recipient of a Phil Zacharia postdoctoral fellowship. A.H. is an incumbent of the Carl and Dorothy Bennett Professorial Chair in Biochemistry. K.R.W. is supported by Cancer Research UK. We thank the Institute of Cancer Research Hybridoma Unit for monoclonal antibody production and A. Friesem and A. Pe'er for useful discussion.

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Correspondence to Amnon Horovitz.

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Rivenzon-Segal, D., Wolf, S., Shimon, L. et al. Sequential ATP-induced allosteric transitions of the cytoplasmic chaperonin containing TCP-1 revealed by EM analysis. Nat Struct Mol Biol 12, 233–237 (2005).

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