Multi-Scale Simulations Provide Supporting Evidence for the Hypothesis of Intramolecular Protein Translocation in GroEL/GroES Complexes

Abstract

The biological function of chaperone complexes is to assist the folding of non-native proteins. The widely studied GroEL chaperonin is a double-barreled complex that can trap non-native proteins in one of its two barrels. The ATP-driven binding of a GroES cap then results in a major structural change of the chamber where the substrate is trapped and initiates a refolding attempt. The two barrels operate anti-synchronously. The central region between the two barrels contains a high concentration of disordered protein chains, the role of which was thus far unclear. In this work we report a combination of atomistic and coarse-grained simulations that probe the structure and dynamics of the equatorial region of the GroEL/GroES chaperonin complex. Surprisingly, our simulations show that the equatorial region provides a translocation channel that will block the passage of folded proteins but allows the passage of secondary units with the diameter of an alpha-helix. We compute the free-energy barrier that has to be overcome during translocation and find that it can easily be crossed under the influence of thermal fluctuations. Hence, strongly non-native proteins can be squeezed like toothpaste from one barrel to the next where they will refold. Proteins that are already fairly close to the native state will not translocate but can refold in the chamber where they were trapped. Several experimental results are compatible with this scenario, and in the case of the experiments of Martin and Hartl, intra chaperonin translocation could explain why under physiological crowding conditions the chaperonin does not release the substrate protein.

Human Hsp10 and Early Pregnancy Factor (EPF) and their relationship and involvement in cancer and immunity: Current knowledge and perspectives

“…For this reason, prokaryotic and eukaryotic cells have evolved special multimolecular chaperone complexes that capture and refold partially folded or unfolded proteins (Horwich et al 2007;). An important class of chaperone molecules is represented by the cage chaperones or chaperonins, e.g., the mitochondrial Hsp60-Hsp10 complex (Horwich et al 2007;Coluzza et al 2008). These complexes accept unfolded, partially folded and misfolded client proteins into their central cavity, which is barely larger than the client proteins (substrate), and assist them in the folding process.…”

“…The process is selective since chaperonins can distinguish proteins that are not in a native conformation from those that are correctly folded. The chaperonin complex does not release the substrate protein before it reaches the native state, preventing aggregation Horwich et al 2007;Coluzza et al 2008).…”

“…1. Typically, after about 15 s the GroES cap and the folded protein are released while the opposite GroEL ring is being occupied by a client polypeptide and then capped with a single GroES ring to initiate a second folding cycle (Horwich et al 2007;Coluzza et al 2008). A single cycle of the GroEL/ GroES chaperoning process hydrolyses seven ATPs (Lin et al 2001;Coluzza et al 2008).…”

“…In the mitochondria of eukaryotic cells, two ring-like structures (each one made of seven Hsp60 subunits) capped by one ring of seven Hsp10 subunits, form a bell-shaped chaperonin structure (Azem et al 1995;Coluzza et al 2008). The Hsp60-Hsp10 complex is responsible for accelerating the folding of polypeptides within mitochondria, re-folding of denaturated proteins, and reducing aggregation of non-native polypeptides and partially unfolded kinetically trapped intermediates.…”

Molecular cloning, mRNA expression, and characterization of heat shock protein 10 gene from humphead snapper Lutjanus sanguineus

“…HSP10 combined with HSP60 constitute the mitochondrial chaperonin complex, which is one of the most important molecular chaperones in eukaryotic cells, play important roles in protein quality control and involved in mitochondrial protein folding (Corrao et al, 2010). In the mitochondria of eukaryotic cells, one ring of seven HSP10 subunits capped by two ring-like structures (each one made of seven HSP60 subunits) form a bell-shaped chaperonin structure (Azem et al, 1995;Coluzza et al, 2008). The assembly of monomeric HSP10 in the heptamer requires intra-and inter-molecular interactions.…”