Conformational changes of the α 1-proteinase inhibitor affecting its cholesterol binding ability

Abstract

The effect of conformational changes of the α 1-proteinase inhibitor (α 1pI) on α 1PI-cholesterol complex (1:2 mol mol ) formation in vitro was studied with electrophoretic and gel Chromatographic methods. Native α 1PI was modified by adding free thiol agents such as glutathione, cysteine HCl, or dl-homocysteine, by heating, or by cleavage with pancreatic elastase or trypsin. Conformational changes of the α 1PI molecule induced by these procedures were all accompanied by a loss of its ability to bind cholesterol in vitro under standard experimental conditions. The data suggest α 1PI-cholesterol binding to be affected by both direct and indirect modifications of the α 1PI-reactive center, that is situated on a mobile peptide loop.