Conformational changes of the α1-proteinase inhibitor affecting its cholesterol binding ability

Abstract
The effect of conformational changes of the α1‐proteinase inhibitor (α1pI) on α1PI‐cholesterol complex (1:2 mol/mol) formation in vitro was studied with electrophoretic and gel Chromatographic methods. Native α1PI 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 α1PI 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 α1PI‐cholesterol binding to be affected by both direct and indirect modifications of the α1PI‐reactive center, that is situated on a mobile peptide loop.