Solution structure of BID, an intracellular amplifier of apoptotic signaling

We report the solution structure of BID, an intracellular cross-talk agent that can amplify FAS/TNF apoptotic signal through the mitochondria death pa thway after Caspase 8 cleavage. BID contains eight alpha helices where two central hydrophobic helices are surrounded by six amphipathic ones. The fol d resembles pore-forming bacterial toxins and shows similarity to BCL-X-L a lthough sequence homology to BCL-X-L is limited to the 16-residue BH3 domai n. Furthermore, we modeled a complex of BCL-X-L and BID by aligning the BID and BAK BH3 motifs in the known BCL-X-L-BAK BH3 complex. Additionally, we show that the overall structure of BID is preserved after cleavage by Caspa se 8. We propose that BID has both BH3 domain-dependent and -independent mo des of action in inducing mitochondrial damage.