Recognizing and Correcting Mistakes

in vivo "in life"; in a Careful study, both in vivo and in the test tube, has demonstrated that mol-

living ^ organism, ratter ecular chaperones bind to their non-native substrate proteins by recognizing exposed non-polar surfaces ("non-polar" means that they are not attracted to water). In correctly folded proteins, these surfaces are usually buried away from the watery environment surrounding the protein. Chap-soluble in water erones promote correct folding of their substrate proteins by unfolding incorrect polypeptide chain conformations, and, in some cases, by providing a sequestered environment in which correct protein folding can occur. The activity of chaperones often requires the binding and hydrolysis of adenosine triphosphate (ATP).

Although only 20 to 30 percent of polypeptide chains require the assistance of a chaperone for correct folding under normal growth conditions, molecular chaperones are absolutely required for cell viability. Discussed than in a laboratory apparatus non-polar without charge separation; not


below are a few of the most common classes of molecular chaperones and their effects on protein folding in the cell.

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