Apart from the name for a romantic
bouncer, it is also a class of proteins necessary for
folding. Although some
proteins fold by themselves, many large and/or complex proteins need some help. Logically, there must be some proteins that
self-assemble in the cell otherwise there would be a 'folder paradox'. That is, "who folds the folder"? (like
who guards the guardians?).
Indeed, chaperones themselves are multisubunit structures whose components fold separately (or are folded by other chaperones? - bootstrapping). They have to be large enough to contain an unfolded protein, thought to be in a molten globule state, and pull it apart. This chaperone-globule complex has been observed for GroEl although not all chaperones catalyse folding this way. Global cell chaperones are non-specific, and take on any protein that comes their way. There are specific types, however, that fold only one family (eg steroid receptors).
There is some naming confusion, due to their origional name of 'heat shock proteins' (HSPs) and subsequent name divergence of chaperones to chaperonins! The HSP60 / GroEl / Thermosome type are called chaperonins while the others are HSP70 / Dnak / Bip ....