Department of Chemistry and Chemical Biology, McMaster University, Hamilton, Canada; Biological Sciences, Sunnybrook Research Institute, Toronto, Canada
Dang Nguyen
Biological Sciences, Sunnybrook Research Institute, Toronto, Canada; Department of Medical Biophysics, University of Toronto, Ontario, Canada
Biological Sciences, Sunnybrook Research Institute, Toronto, Canada; Department of Medical Biophysics, University of Toronto, Ontario, Canada
Elizabeth J Osterlund
Biological Sciences, Sunnybrook Research Institute, Toronto, Canada; Department of Biochemistry, University of Toronto, Toronto, Canada
Qian Liu
Biological Sciences, Sunnybrook Research Institute, Toronto, Canada
Hetal Brahmbhatt
Department of Chemistry and Chemical Biology, McMaster University, Hamilton, Canada; Biological Sciences, Sunnybrook Research Institute, Toronto, Canada; Department of Medicine, McMaster University, Hamilton, Canada
Zhi Zhang
Department of Biochemistry, University of Oklahoma Health Sciences Center, Oklahoma City, United States; Molecular Biology and Stephenson Cancer Center, University of Oklahoma Health Sciences Center, Oklahoma City, United States
Department of Biochemistry, University of Oklahoma Health Sciences Center, Oklahoma City, United States; Molecular Biology and Stephenson Cancer Center, University of Oklahoma Health Sciences Center, Oklahoma City, United States
Brian Leber
Department of Medicine, McMaster University, Hamilton, Canada
Biological Sciences, Sunnybrook Research Institute, Toronto, Canada; Department of Medical Biophysics, University of Toronto, Ontario, Canada; Department of Biochemistry, University of Toronto, Toronto, Canada
The Bcl-2 family BH3 protein Bim promotes apoptosis at mitochondria by activating the pore-forming proteins Bax and Bak and by inhibiting the anti-apoptotic proteins Bcl-XL, Bcl-2 and Mcl-1. Bim binds to these proteins via its BH3 domain and to the mitochondrial membrane by a carboxyl-terminal sequence (CTS). In cells killed by Bim, the expression of a Bim mutant in which the CTS was deleted (BimL-dCTS) triggered apoptosis that correlated with inhibition of anti-apoptotic proteins being sufficient to permeabilize mitochondria isolated from the same cells. Detailed analysis of the molecular mechanism demonstrated that BimL-dCTS inhibited Bcl-XL but did not activate Bax. Examination of additional point mutants unexpectedly revealed that the CTS of Bim directly interacts with Bax, is required for physiological concentrations of Bim to activate Bax and that different residues in the CTS enable Bax activation and binding to membranes.
