Molecular chaperones, also known as heat shock proteins, are a set of highly conserved proteins that help prevent the formation of misfolded proteins as well as the aggregation of non-folded proteins. newly synthesized folded proteins with other unfolded proteins. in the cell (Hartl 1996). These misfolded/unfolded proteins usually have their hydrophobic residues on their surface, as opposed to correctly folded proteins which have a hydrophobic core and hydrophilic residues on their surface. As a result, these surface hydrophobic residues within these misfolded/unfolded proteins are exposed to the solvent present in the cell and can interact with other misfolded/unfolded proteins. Molecular chaperones are therefore fundamental proteins because they bind to the misfolded/unfolded protein at its hydrophobic residues exposed to the solvent and, since molecular chaperones are ATPases, they catalyze the hydrolysis of ATP through which they facilitate the correct folding of the protein into its native state. . Binding of molecular chaperones to hydrophobic residues in the protein prevents protein aggregation. A class that belongs to molecular chaperones is known as chaperonins which form large, cage-like multisubunit structures in eubacteria, mitochondria, chloroplasts, and in the eukaryotic cytosol. The bacterial chaperonin is known as GroEL (L for large) and it performs its function with its co-chaperonin GroES (S for small). These two elements are expressed from the GroE operon in Escherichia coli. In eukaryotes, the heat shock proteins Hsp60 and Hsp10 are homologous to GroEL and GroES, respectively, because their structure and function are almost identical. The first high-resolution structure of GroEL was solved in 1994 at a resolution of 2.8 Å. T...... middle of paper ......bic, they are able to bind to the exposed hydrophobic surface of the non-native polypeptide. Mutations that replace these nonpolar amino acids with polar residues result in the abolition of the polypeptide bond. The second phase involves the binding of the co-chaperonin GroES with seven ATP molecules in the presence of Mg2+ to a GroEL ring. Binding of GroES depends on ATP binding to nucleotide binding sites in the cis ring of GroEL. When these sites are completely saturated, ATP molecules are free to enter and exit them without any steric obstruction. Weak ATP binding to GroEL is sufficient to trigger a rapid conformational change that allows rapid association of GroES. Binding of GroES causes the F and M helix residues of the middle domain to attach to the equatorial domain and close the binding sites in the cis ring..