Proteins and Enzymes

ID #2177

If cysteine is an uncharged/nonpolar/hydrophobic R-group with a sulfur on the outside, how is it possible that a cysteine on one polypeptide can interact with another cysteine on another polypeptide (creating a disulfide linkage between the two polypeptides) if the two cysteines should be "hidden" from the aqueous environment within their respective polypeptides' tertiary levels of folding?

Great question! Fortunately, cells have a way to overcome this problem. Enzymes (called chaperones) often aid a protein in its proper folding. In the case of the formation of a covalent disulfide bond, these enzymes can refold a protein to bring the two cysteines into close proximity to each other. The formation of this disulfide bridge does not occur spontaneously in the cell, enzymes are necessary to catalyze the formation of this type of bond as well.

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