Members of the serine proteinase inhibitor or serpin superfamily have a common molecular
architecture based on a dominant five-membered A β-pleated sheet and a mobile reactive
center loop. The reactive center loop has been shown to adopt a range of conformations
from the three turn α-helix of ovalbumin to the cleaved or latent inhibitor in which the reactive
center loop is fully inserted into the A sheet of the molecule. While the cleaved state can be
achieved in all inhibitory serpins only plasminogen activator inhibitor-1 and, more recently …