ATP-, K+-dependent heptamer exchange reaction produces hybrids between GroEL and chaperonin from Thermus thermophilus

Chaperonin from Thermus thermophilus (Tcpn60(14).Tcpn10(7)) splits at the plane between two Tcpn60(7) rings into two parts in a solution containing ATP and K+ (Ishii, N., Taguchi, H., Sasabe, H., and Yoshida, M. (1995) FEBS Lett. 362, 121-125). When Escherichia coli GroEL(14) was additionally included in the solution described above, hybrid chaperonins GroEL(7).Tcpn60(7) and GroEL(7).Tcpn60(7).Tcpn10(7) were formed rapidly (<20 s) at 37 degrees C. The hybrid was also formed from Tcpn60(14) and GroEL(14) but not from a mutant GroEL(14) lacking ATPase activity. The hybrid formation was saturated at similar to 300 mu M ATP and similar to 300 mM K+. These results imply that GroEL(14) also splits and undergoes a heptamer exchange reaction with Thermus chaperonin under nearly physiological conditions, Similar to parent chaperonins, the isolated hybrid chaperonins exhibited ATPase activity that was susceptible to inhibition by Tcpn10(7) or GroES(7) and mediated folding of other proteins, Once formed, the hybrid chaperonins were stable, and the parent chaperonins were not regenerated from the isolated hybrids under the same conditions in which the hybrids had been formed, Only under conditions in which GroEL in the hybrids was selectively destroyed, such as incubation at 70 degrees C, Thermus chaperonin, but not GroEL(14), was regenerated from the hybrid. Therefore, the split reaction may not be an obligatory event repeated in each turnover of the chaperonin functional cycles but an event that occurs only when chaperonin is first exposed to ATP/K+.