Serpins flex their muscle: I. Putting the clamps on proteolysis in diverse biological systems

Serpins comprise the largest superfamily of peptidase inhibitors and are well known as regulators of hemostasis and thrombolysis. Studies using model organisms, from plants to vertebrates, now show that serpins and their unique inhibitory mechanism and conformational flexibility are exploited to control proteolysis in molecular pathways associated with cell survival, development and host defense. In addition, an increasing number of non-inhibitory serpins are emerging as important elements within a diversity of biological systems by serving as chaperones, hormone transporters or anti-angiogenic factors.