Heat shock protein 47 : a chaperone for the fibrous cap?

According to The American Heritage College Dictionary,1 a chaperone is “a guide or companion whose purpose is to ensure propriety or restrict activity.” The term “molecular chaperone” is applied to proteins that control the proper folding of nascent polypeptides into the correct 3D structure (ensure propriety) or maintain polypeptides in an inactive state (restrict activity) until they have been transported to their ultimate intracellular or extracellular destinations and assembled into functional multiprotein complexes.2 Many of the proteins that function as molecular chaperones were originally identified as “heat shock proteins” (Hsps), because their abundance increased in cells subjected to thermal stress. Individual members of the extended Hsps are usually identified by reference to their molecular mass (eg, Hsp70, Hsp90, etc). The terminology can be misleading because not all Hsps are heat-inducible, not all chaperones are called Hsps, and diverse forms of cellular stress other than elevated temperature lead to transcriptional and post-transcriptional regulation of chaperone synthesis.