Serpins: mobile conformations in a family of proteinase inhibitors

Abstract

Abstract The serpins are unique among the families of serine proteinase inhibitors in having a reactive centre that is situated on a mobile peptide loop. The structures of three alternative conformations are now known, and it can be deduced that the active form involves the partial insertion of the loop into the A sheet of the molecule. The ability of the loop to move in and out of this sheet has been adapted by e inhibitory activity. Mutations that affect the movement of the loop cause a loss of inhibitory activity, and other mutations can result in an opening of the A sheet and consequent loop-sheet intermolecular polymerization.