Manduca sexta Serpin-3 Regulates Prophenoloxidase Activation in Response to Infection by Inhibiting Prophenoloxidase-activating Proteinases

Many serine proteinase inhibitors of the serpin superfamily have evolved in vertebrates and invertebrates to regulate serine proteinase cascades that mediate the host defense responses. We have isolated an immuneresponsive serpin from the tobacco hornworm, Manduca sexta. This inhibitor, M. sexta serpin-3, contains a reactive site loop strikingly similar to the proteolytic activation site in prophenoloxidase (pro-PO). Molecular cloning and...