In biology, chaperones are peculiar proteins whose function is to assist other proteins in achieving proper folding. They have been discovered in being heat shock proteins, that is, proteins expressed in heat shock conditions. The reason for this behaviour is that protein folding is severly affected by heat, and therefore chaperones act to counteract the potential damage. Although most proteins can fold in absence of chaperones, a minority strictly requires them.
A large number of chaperones need ATP for proper function. However, chaperones are quite diverse and there is still considerable debate and uncertainity on how they function.
Chaperones recognize unfolded proteins by the hydrophobic residues these expose to the solvent. Exposed hydrophobic residues are unnatural for properly folded proteins, which should expose hydrophilic aminoacids only.
In former times, a chaperone was an older woman who accompanied a young unmarried woman on social occasions, especially when there were men present. See chaperon.