In this study, we report the simultaneous refolding and reconstitution of the recombinant Bax inhibitor-1 (BI-1) from inclusion bodies expressed in Escherichia coli. A functional assay showed that the resulting proteoliposomes responded to acidic conditions and triggered the release of entrapped Ca2+ from liposomes. The secondary structure of the reconstituted BI-1 was also determined using circular dichroism, which revealed an increase of alpha-helix content and a decrease of random structure when exposed to acidic solutions. These conformational changes may be responsible for the proton ion-induced Ca2+ release of BI-1. (C) 2009 Published by Elsevier Inc.