The peptidase zymogen proregions: Nature's way of preventing undesired activation and proteolysis

Since the initial description of a peptidase activity, namely pepsin, in the middle of the 19(th) century, our understanding of the molecular basis of peptidase function and activation has greatly improved. Further, by sequencing entire genomes, we have reached a stage whereby it is now possible to appreciate the tremendous diversity and unique specificities of peptidases. Because of their importance in most if not all vital processes of the cell including ultimately its death, their activities must be carefully localized and kept under tight control. In addition to endogenous inhibitors, control of enzymatic activity can be achieved through their synthesis and transport as inactive zymogens. This review article will focus on the characteristics as well as the role of the proregion contained within the peptidase zymogen structure. It will survey novel zymogen structures determined in the past 5 years as well as those of selected emerging peptidase families for which there exists as yet no or little structural data. These include members belonging to the caspase, ADAMS, TTSP, MMP, Aspartyl peptidases and convertase families.