Figure 2.

Characterization of the minichaperone. (A) Thermal denaturation of sht-GroEL_191–345 monitored by circular dichroism at 222 nm. The midpoint of thermal denaturation (T_m) for sht-GroEL_191–345 is 69°C, as determined by fitting the circular dichroism signal to a two state transition model. Note, throughout the figures sht-GroEL_191–345 is indicated by sht345. (B) Effect of various chaperones on cyclophilin (CyPA) folding. CyPA denatured in 4.8 M guanidine-HCl was rapidly diluted (50-fold) into buffer A containing the indicated chaperones. The final concentration of CyPA was 1 μM, and the concentrations of chaperones present were: 0 μM GroEL (Spont.); 7 μM GroEL protomer (EL); 4 μM sht-GroEL_191–345 (sht345); 100 μg/ml α-casein (casein). Folding reactions were carried out at 25°C. CyPA activities are reported as the fraction of the input material.