GroEL and GroES. By: Jim, Alan, John. Background. Proteins fold spontaneously to their native states, based on information in their amino acid sequence Sometimes proteins fail to fold and need help Cells have developed molecules that catalyse protein folding called chaperones .
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By: Jim, Alan, John
Chaperones themselves contain no information about particular folding patterns, rather they anneal misfolded proteins and allow them to find their native state.Background
When seen separate from GroES, the GroEL ring is in an open state, allowing for the entry of proteins. The inside of the Gro-EL ring has a flexible hydrophobic lining. This allows for the binding of misfolded proteins, through hydrophobic and van der Waals interactions. Throughout these processes, however, it is possible for the protein to become unfolded partially, when in an incorrect state.
With the binding of ATP and GroES, the cap (GroES) is ready for the ring (GroEL), however, there must first be a conformational change in the cis ring. The ending result is a closed cavity where the “substrate protein” can refold, once it is released from the apical domains. It must also be taken away from potential aggregation partners.
When the cis ring undergoes the conformational change, it more than doubles the available volume of the cavity. This allows for larger unfolding/refolding transition states to exist.
The inside of the GroEL cavity also changes from hydrophobic to hydrophilic. This peels the bound misfolded protein off of the surface and unfolds it even further.
“The burial of the original interior GroEL surface in intersubunit contacts within the GroEL-GroES complex itself breaks the binding of the protein to the original hydrophobic internal surface, leaving a macroclathrate complex.” This new complex (cavity) is composed of a crystal lattice, housing the protein in the cavity.
Finally, hydrolysis of ATP in the cis ring allows for the weakening of the structure. Binding of the ATP in the trans ring causes the disassembly of the cis assembly, allowing for the release of the GroES and substrate protein. In the end, the ring is left in original state.
It needs to be noted that through the process, there is a necessity of seven or fourteen ATP molecules. In the end, the cost is much larger than the energy required to unfold a protein. However, it needs to be stated that it this cost is infinitely smaller than the death of a cell, and is also quite smaller than the synthesis of the polypeptide chain.