ATP BINDING INDUCES LARGE CONFORMATIONAL-CHANGES IN THE APICAL AND EQUATORIAL DOMAINS OF THE EUKARYOTIC CHAPERONIN CONTAINING TCP-1 COMPLEX

The chaperonin-containing TCP-I complex (CCT) is a heteromeric particl e composed of eight different subunits arranged in two back-to-back 8- fold pseudo-symmetric rings. The structural and functional implication s of nucleotide binding to the CCT complex was addressed by electron m icroscopy and image processing. Whereas ADP binding to CCT does not re veal major conformational differences when compared with nucleotide-fr ee CCT, ATP binding induces large conformational changes in the apical and equatorial domains, shifting the latter domains up to 40 degrees (with respect to the interring plane) compared with 10 degrees for nuc leotide-free CCT or ADP-CCT. This equatorial ATP-induced shift has no counterpart in GroEL, its prokaryotic homologue, which suggests differ ences in the folding mechanism for CCT.