title: The C terminus of Bax inhibitor-1 forms a Ca2+-permeable channel pore.
abstract: 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.
authors: Department of Molecular Cell Biology, Laboratory of Molecular and Cellular Signaling, K.U. Leuven, B-3000 Leuven, Belgium. geert.bultynck@med.kuleuven.be
authors: Geert
authors: G
authors: Bultynck
authors: Santeri
authors: S
authors: Kiviluoto
authors: Nadine
authors: N
authors: Henke
authors: Hristina
authors: H
authors: Ivanova
authors: Lars
authors: L
authors: Schneider
authors: Volodymyr
authors: V
authors: Rybalchenko
authors: Tomas
authors: T
authors: Luyten
authors: Koen
authors: K
authors: Nuyts
authors: Wim
authors: W
authors: De Borggraeve
authors: Ilya
authors: I
authors: Bezprozvanny
authors: Jan B
authors: JB
authors: Parys
authors: Humbert
authors: H
authors: De Smedt
authors: Ludwig
authors: L
authors: Missiaen
authors: Axel
authors: A
authors: Methner
mesh_terms: D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism*; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D010449:Peptide Mapping; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010944:Plants / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015003:Yeasts / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D008051:Lipid Bilayers; D008565:Membrane Proteins; D010455:Peptides; C490015:Tmbim6 protein, mouse; D002118:Calcium