BID Protein, Human expresses in E. coli. The BH3-only protein BID, a pro-apoptotic member of the Bcl-2 family, was initially discovered through binding to both pro-apoptotic Bax and anti-apoptotic Bcl-2. BID is activated in the BCL-2-regulated or mitochondrial apoptosis pathway and acts as a switch between the extrinsic and intrinsic cell death pathways[1].