 Like other serpins, PAI-2 has three beta sheets (A, B, C) and nine alpha helices (hA-hI).The structure of PAI-2 mutants have been solved, in which the 33-amino acid loop connecting helices C and D is deleted.This CD-loop is particularly flexible and difficult to stabilize, as the loop is known to translocate up to 54 Å during the formation of intramolecular disulfide bonds.