IN-VITRO AMYLOID FIBRIL FORMATION FROM ALPHA(1)-ANTITRYPSIN

We have previously shown that the interaction between alpha(1)-antitry psin (AAT) and lithocholic acid (LA) results in changes of AAT propert ies leading to its polymerization and inactivation. To define the stru ctural rearrangements of AAT induced by such interaction, we studied t he in vitro binding between AAT and LA at molar ratio 1:5 for varying time intervals at a physiological pH. Complex formation was shown by e lectrophoretic techniques and autoradiography. Studies of the AAT in c omplex with LA by using far-UV spectra circular dichroism and fluoresc ence measurements indicated an increase of beta-structure of AAT and p ronounced changes in surroundings of the chromophores. In addition, co mplexed AAT showed increase in thermal stability, compatible with that after proteolytic cleavage. Characterization of the AAT-LA complexes by Congo red binding, polarization and negative staining electron micr oscopy provided clear evidence that AAT, under chosen experimental con ditions, can self-assemble into amyloid fibrils, compatible with accep ted models of fibrillar structures. This propensity of AAT to form sta ble p-structures in a hydrophobic surrounding may contribute to improv ed characterization of various amyloid deposits occurring in vivo and be a guide for understanding details of structure-function relationshi ps in the intact AAT-molecule.