Bim escapes displacement by BH3-mimetic anti-cancer drugs by double-bolt locking both Bcl-XL and Bcl-2

Elife. 2019 Mar 12:8:e37689. doi: 10.7554/eLife.37689.


Tumor initiation, progression and resistance to chemotherapy rely on cancer cells bypassing programmed cell death by apoptosis. We report that unlike other pro-apoptotic proteins, Bim contains two distinct binding sites for the anti-apoptotic proteins Bcl-XL and Bcl-2. These include the BH3 sequence shared with other pro-apoptotic proteins and an unexpected sequence located near the Bim carboxyl-terminus (residues 181-192). Using automated Fluorescence Lifetime Imaging Microscopy - Fluorescence Resonance Energy Transfer (FLIM-FRET) we show that the two binding interfaces enable Bim to double-bolt lock Bcl-XL and Bcl-2 in complexes resistant to displacement by BH3-mimetic drugs currently in use or being evaluated for cancer therapy. Quantifying in live cells the contributions of individual amino acids revealed that residue L185 previously thought involved in binding Bim to membranes, instead contributes to binding to anti-apoptotic proteins. This double-bolt lock mechanism has profound implications for the utility of BH3-mimetics as drugs. ​.

Keywords: BH3-mimetic drugs; Bcl-2 family proteins; Forster resonance energy transfer; apoptosis; cancer biology; cell biology; fluorescence lifetime imaging; none; tissue culture cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Apoptosis
  • Apoptosis Regulatory Proteins / chemistry
  • Bcl-2-Like Protein 11 / chemistry*
  • Cell Line, Tumor
  • Disease Progression
  • Drug Resistance, Neoplasm*
  • Fluorescence Resonance Energy Transfer
  • Humans
  • Image Processing, Computer-Assisted
  • MCF-7 Cells
  • Neoplasms / drug therapy*
  • Protein Domains
  • Proto-Oncogene Proteins c-bcl-2 / chemistry*
  • bcl-X Protein / chemistry*


  • Antineoplastic Agents
  • Apoptosis Regulatory Proteins
  • BCL2 protein, human
  • BCL2L1 protein, human
  • BCL2L11 protein, human
  • Bcl-2-Like Protein 11
  • Proto-Oncogene Proteins c-bcl-2
  • bcl-X Protein