Equatorial split of holo-chaperonin from Thermus thermophilus by ATP and K+.

Holo-chaperonin molecule from Thermus thermophilus is a bullet-shaped particle whose cylinder part and round top are composed of two stacked rings of the cpn60 heptamer and a single ring of the cpn10 heptamer, respectively. We found that it splits at the plane between two cpn60 rings into two halves under physiological conditions, that is, in the presence of ATP (but not AMP-PNP, ADP) + K+ (but not Na+) at 60 degrees C. This equatorial split could be functionally important although it has not been considered in any current mechanistic model of chaperonin functioning.