1.A.21.2.4
BH3-interacting domain death agonist isoform 2, BID, of 195 aas and 2 or 3 TMSs. BCL-2 family proteins display structural homology to channel-forming bacterial toxins, such as colicins, the transmembrane domain of diphtheria toxin, and the N-terminal domain of delta-endotoxin. By analogy, it has been hypothesized the BCL-2 family proteins would unfold and insert into the lipid bilayer upon membrane association. Oh et al. 2005 showed that helices 6-8 maintain an alpha-helical conformation in membranes with a lipid composition resembling mitochondrial outer membrane contact sites. However, unlike colicins and the transmembrane domain of diphtheria toxin, these helices of BID are bound to the lipid bilayer without adopting a transmembrane orientation.