The Mechanism of α1-Antitrypsin Polymerization Probed by Fluorescence Spectroscopy

The polymerization of α1-antitrypsin within the hepatic cell leads to α1-antitrypsin deficiency. Both the conformational changes and the kinetics of the polymerization process are poorly understood. Here we describe fluorescence experiments investigating the polymerization reaction using the fluorescent probe4,4′-dianilino-1,1′-binaphthyl-5,5′-disulfonate (bis-ANS) which bound to both native and polymerized α1-antitrypsin. Biphasic changes in bis-ANS fluorescence were observed during formation of α1-antitrypsin polymers. Initially a rapid increase in fluorescence signal was observed; it was followed by a gradual reduction in fluorescence signal. The first phase is a conformational change in which the A β-sheet of α1-antitrypsin opens, whereas the second phase represents the insertion of the reactive center loop into the A β-sheet of another molecule and therefore determines the rate of the polymerization process.