Increased Efficiency of GroE-assisted Protein Folding by Manganese Ions(*)

This study addresses the role of ATP-bound and free Mg²⁺ and Mn²⁺ ions in the activation and modulation of chaperonin-assisted refolding of urea-denatured malate dehydrogenase. As compared with Mg²⁺, Mn²⁺ ions caused a significant increase in the rate of GroE-assisted malate dehydrogenase refolding and, concomitantly, a decrease in the rate of ATP hydrolysis. Moreover, Mn²⁺ increases the affinity of GroES for GroEL, even in the presence of saturating amounts of Mg²⁺. Chemical cross-linking showed that lower concentrations of Mn-ATP as compared with Mg-ATP are needed to form both asymmetric GroEL₁₄GroES₇ and symmetric GroEL₁₄(GroES₇)₂ particles. The manganese-dependent increase in the rate of protein folding concurred with a specific increase in the amount of symmetric GroEL₁₄(GroES₇)₂ particles detected in a chaperonin solution. Thus, Mn²⁺ is a cofactor that can markedly increase the efficiency of the chaperonin reaction in vitro. Mn²⁺ ions can serve as an important tool for analyzing the molecular mechanism and the structure of chaperonins.