The C terminus of Bax inhibitor-1 forms a Ca2+-permeable channel pore

J Biol Chem. 2012 Jan 20;287(4):2544-57. doi: 10.1074/jbc.M111.275354. Epub 2011 Nov 28.


Bax inhibitor-1 (BI-1) is a multitransmembrane domain-spanning endoplasmic reticulum (ER)-located protein that is evolutionarily conserved and protects against apoptosis and ER stress. Furthermore, BI-1 is proposed to modulate ER Ca(2+) homeostasis by acting as a Ca(2+)-leak channel. Based on experimental determination of the BI-1 topology, we propose that its C terminus forms a Ca(2+) pore responsible for its Ca(2+)-leak properties. We utilized a set of C-terminal peptides to screen for Ca(2+) leak activity in unidirectional (45)Ca(2+)-flux experiments and identified an α-helical 20-amino acid peptide causing Ca(2+) leak from the ER. The Ca(2+) leak was independent of endogenous ER Ca(2+)-release channels or other Ca(2+)-leak mechanisms, namely translocons and presenilins. The Ca(2+)-permeating property of the peptide was confirmed in lipid-bilayer experiments. Using mutant peptides, we identified critical residues responsible for the Ca(2+)-leak properties of this BI-1 peptide, including a series of critical negatively charged aspartate residues. Using peptides corresponding to the equivalent BI-1 domain from various organisms, we found that the Ca(2+)-leak properties were conserved among animal, but not plant and yeast orthologs. By mutating one of the critical aspartate residues in the proposed Ca(2+)-channel pore in full-length BI-1, we found that Asp-213 was essential for BI-1-dependent ER Ca(2+) leak. Thus, we elucidated residues critically important for BI-1-mediated Ca(2+) leak and its potential channel pore. Remarkably, one of these residues was not conserved among plant and yeast BI-1 orthologs, indicating that the ER Ca(2+)-leak properties of BI-1 are an added function during evolution.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / chemistry
  • Calcium / metabolism*
  • Calcium Channels / chemistry
  • Calcium Channels / genetics
  • Calcium Channels / metabolism*
  • Endoplasmic Reticulum / chemistry
  • Endoplasmic Reticulum / genetics
  • Endoplasmic Reticulum / metabolism*
  • Evolution, Molecular
  • HeLa Cells
  • Humans
  • Intracellular Membranes / chemistry
  • Intracellular Membranes / metabolism*
  • Lipid Bilayers / chemistry
  • Lipid Bilayers / metabolism
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mice
  • Peptide Mapping
  • Peptides / chemistry
  • Peptides / genetics
  • Peptides / metabolism
  • Plants / chemistry
  • Plants / genetics
  • Plants / metabolism
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Yeasts / chemistry
  • Yeasts / genetics
  • Yeasts / metabolism


  • Calcium Channels
  • Lipid Bilayers
  • Membrane Proteins
  • Peptides
  • Tmbim6 protein, mouse
  • Calcium