Chaperonin from Thermus thermophilus can protect several enzymes from irreversible heat denaturation by capturing...

Chaperonin isolated from Thermus thermophilus is stable up to 80 degrees C. Taking advantage of this heat stability, we have studied the effects of chaperonin on heat denaturation of several relatively heat labile enzymes. When the enzymes are incubated at their denaturating temperatures, the presence of T. thermophilus chaperonin in the solution has little effect on the rate of apparent inactivation of the enzyme. However, this inactivation is not irreversible since most activity is recovered when the solution is shifted to the second incubation at a moderate temperature with concomitant addition of MgATP. When the chaperonin is omitted from the solution, no recovery is observed. Recovery of the activity is also dependent on MgATP in the second incubation and 50% of recovery is attained at 5 microM MgATP. When the chaperonin is added after starting the incubation at a denaturing temperature, recovery of the activity becomes poorer as the delay of chaperonin addition increases. The critical temperature of the incubation at which irreversible denaturation occurs to the enzymes is elevated 8-15 degrees C by inclusion of T. thermophilus chaperonin in the solution. The heat stability of captured proteins by the chaperonin, assessed as retention of the ability to resume productive folding under optimal conditions, is measured more accurately using chemically produced folding intermediate-chaperonin complexes. The ability is lost at about 78 degrees C being irrespective of variable heat stability of individual enzymes. These results indicate that during heat denaturation proteins assume a common structure which is recognizable by the chaperonin. Once a protein with this structure is captured by T. thermophilus chaperonin, it retains the ability to resume productive folding even after exposure to the otherwise denaturing high temperature. Its heat stability seems to be limited solely by heat stability of chaperonin.