a, Structure and sequence of Bid SAHBA. The native methionine of Bid BH3 was replaced with norleucine (NL) in Bid SAHBA due to the incompatibility of sulfur with the metathesis reaction. b, Fluorescence polarization binding assays were carried out using FITC-labeled peptides (50 nM) and full-length Bax. Direct interaction between Bid SAHBA and Bax was observed. c, Comparison of the inactive form of Bax (PDB: 1F16) and activated form of BaxΔ21 (PDB: 4BD2). The crystal structure of Bid BH3 peptide (SESQEDIIRNIARHLAQVGDSMDRSIPPGL) complexed with BaxΔ21 shows that Hα1-Hα5 are released from Hα6-Hα8. Reproduced, with permission, from REF. 147© the Elsevier Inc. (2006).