Characterisation of Cpn60 (GroEL) bound cytochrome c: the passive role of molecular chaperones in assisted folding/refolding of proteins

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Abstract
Molecular chaperone GroEL and cytochrome c were shown to form a stable complex at low ionic strength which was structurally characterised by means of UV-visible, CD and fluorescence spectroscopy. GroEL-bound cytochrome c was demonstrated to be in a compact, non-native state which could correspond to GroEL-bound forms of two well known cytochrome c folding intermediates IH NC and I*. These were selectively released from GroEL using adenosine 5′-triphosphate and co-chaperone GroES. Drawing from these results and our previous data, a simple passive kinetic partitioning mechanism is proposed for molecular chaperone assisted folding/refolding of substrate proteins in which molecular chaperone GroEL binds to substrate proteins in order to control the steady state concentration of substrate protein folding intermediates below the critical threshold for aggregation, thereby encouraging substrate protein folding intermediates to partition kinetically along routes to correctly folded protein in preference to aggregated states. In this way the yield of correctly folded protein may be maximised, unless the extrinsic folding conditions themselves otherwise prevent this happening by promoting protein misfolding through the formation of incorrect intramolecular interactions.

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