The dynamics of the GroEL‐gp31 chaperonin complex studied with fluorescence spectroscopy

Abstract

The GroEL‐gp31 chaperonin complex, composed of the E. coli GroEL and the bacteriophage T4 encoded gp31, is essential for the folding of the T4 major capsid protein (gp23). Interestingly the E.coli GroEL‐GroES complex cannot satisfy the folding requirements of gp23. Although the amino acid sequence of gp31 and GroES is only 14% identical, their structure is quite similar. Cryo electron microscopy and image reconstruction of the GroEL‐gp31‐ADP complex revealed that the folding cavity is larger than that of the GroEL‐GroES‐ADP complex (Clare, JMB 2006), which is consistent with the size of the capsid protein (56kDa) being close to the maximum size thought to fit inside the folding cage. The folding of gp23 requires a gp31‐dependant cis‐folding mechanism (Bakkes PNAS 2005) but little is known about the dynamics of the GroEL‐gp31 chaperonin complex. Using stopped‐flow fluorescence spectroscopy, we show that the chaperonin‐assisted refolding of eGFP occurs with the same rate and yield with both GroES and gp31. We also show that the dissociation kinetics of gp31 from GroEL are faster than GroES, and that the binding of the gp23 capsid protein accelerates the ATPase cycle of the GroEL‐gp31 chaperonin complex.