Chaperone (protein)

A molecular chaperone is a protein which does things to other proteins. They are mostly concerned with protein folding. Hartl F.U. 1996. Molecular chaperones in cellular protein folding. Nature 381, 571–579 Bartlett A.L. & Radford S.E. 2009. An expanding arsenal of experimental methods yields an explosion of insights into protein folding mechanisms. Nat. Struct. Mol. Biol. 16, 582–588 Hartl F.U. & Hayer-Hartl M. 2009. Converging concepts of protein folding in vitro and in vivo. Nature Structural & Molecular Biology 16 (6): 574–581.  

Some help assemble or take apart other macromolecular structures. They do not occur in these structures when the structures go about their normal functions. 
What they do is:
Fold over half of all mammalian proteins.
Unfold proteins.
Assemble proteins.
Disassemble proteins.

The first protein to be called a chaperone assists the assembly of nucleosomes from folded histones and DNA.Ellis R.J. 1996. Discovery of molecular chaperones. Cell stress chaperones 1 (3): 155–60. Those assembly chaperones, especially in the nucleus, assemble folded subunits into larger structures such as cell organelles.

One major function of chaperones is to prevent polypeptide chains and subunits sticking together in clumps which do not function. Some chaperones are "holdases" which act to stop aggregation. Others, called "foldases", do help fold proteins which cannot do it themselves. Such proteins violate Anfinsen's dogma, which said protein folding was automatic.

 References 

Category:Molecular biology
Category:Proteins