Intramolecular chaperones: polypeptide extensions that modulate protein folding

Several prokaryotic and eukaryotic proteins are synthesized as precursors i n the form of pre-pro-proteins. While the pre-regions function as sign al p eptides that are involved in transport, the propeptides can often catalyze correct folding of their associated proteins. Such propeptides have been te rmed intramolecular chaperones. In cases where pi propeptides may not direc tly catalyze the folding reaction, it appears that they can facilitate proc esses such as structural organization and oligomerization, localization, so rting and modulation of enzymatic activity and stability of proteins. Based on the available literature it appears that propeptides may actually funct ion as 'post-translational modulators' of protein structure and function. P ropeptides can be classified into two broad categories: Class I propeptides that function as intramolecular chaperones and directly catalyze the foldi ng reaction; and Class II propeptides that are not directly involved in fol ding.