Аннотация:Molecular chaperones are a special class of multifunctional heat shock proteins (Hsps). Apart from other activities, they assist in the folding and quaternary structure building of other proteins, both in vivo and in vitro. Some chaperones (e.g., chaperonins) are complex oligomeric proteins, and their own folding is an intriguing issue. In this chapter, we combine our own results with literature data to describe unfolding and refolding of the most intensively studied chaperonins of E. coli cells: GroEL (Hsp60) and its co-chaperonin GroES (Hsp10). Our studies of equilibrium and kinetic unfolding and refolding reactions of these proteins showed that unfolding and refolding of GroES and GroEL subunits are reversible, while formation of the GroEL quaternary structure requires the presence of chaperonin ligands (Mg2+, ATP, or ADP) and/or a special solvent composition. Moreover, under some conditions (low GroEL concentration, low or moderate ionic strength, or unfavorable temperature), the presence of the co-chaperonin GroES is critical. Also, as shown, reassembly of a two-ring tetradecameric GroEL particle is mediated by formation of a one-ring intermediate capable of interacting with the one-ring co-chaperonin GroES. Stability of this intermediate plays a key role in formation of a two-ring tetradecameric GroEL particle. Refolding of GroES is spontaneous and an order of magnitude faster than that of GroEL. A possible mechanism of in vivo GroEL folding is discussed.