Conformational change in elastase following complexation with alpha1-proteinase inhibitor: a CD investigation

Abstract

The CD spectrum of porcine pancreatic elastase in complex with α1-proteinase inhibitor (α1-PI) was calculated by subtracting the CD spectrum of the proteolytically cleaved inhibitor from that of the elastase—α1-PI complex. Elastase undergoes a moderate secondary structure change: its β-structure is partially disordered while its α-helix content is poorly affected. In contrast, its tertiary structure undergoes a significant structural loosening upon complexation. These alterations have been compared with those following chemical and thermal unfolding of free elastase. Inhibitor-bound elastase and the denaturation intermediate of free elastase share secondary but not tertiary structural features. On the other hand, both free and complexed elastases undergo a single-step transition in tertiary structure upon thermal unfolding. These data are discussed in terms of the inhibition and structural modification of elastase induced by α1-PI observed by previous investigators.