Changing the nature of the initial chaperonin capture complex influences the substrate folding efficiency

Abstract

For the chaperonin substrates, rhodanese, malate dehydrogenase (MDH), and glutamine synthetase (GS), the folding efficiencies, and the lifetimes of folding intermediates were measured with either the nucleotide-free GroEL or the activated ATP · GroEL · GroES chaperonin complex. With both nucleotide- free and activated complex, the folding efficiency of rhodanese and MDH remained high over a large range of GroEL to substrate concentration ratios (up to 1:1). In contrast, the folding efficiency of GS began to decline at ratios lower than 8:1. At ratios where the refolding yields were initially the same, only a relatively small increase (1.6-fold) in misfolding kinetics of MDH was observed with either the nucleotide-free or activated chaperonin complex. For rhodanese, no change was detected with either chaperonin complex. In contrast, GS lost its ability to interact with the chaperonin system at an accelerated rate (8-fold increase) when the activated complex instead of the nucleotide-free complex was used to rescue the protein from misfolding. Our data demonstrate that the differences in the refolding yields are related to the intrinsic folding kinetics of the protein substrates. We suggest that the early kinetic events at the substrate level ultimately govern successful chaperonin-substrate interactions and play a crucial role in dictating polypeptide flux through the chaperonin system. Our results also indicate that an accurate assessment of the transient properties of folding intermediates that dictate the initial chaperonin-substrate interactions requires the use of the activated complex as the interacting chaperonin species.