Yeast Bax Inhibitor (Bxi1p/Ybh3p) is a calcium channel in E. coli.

Abstract

Human Bax Inhibitor‐1 (HsBI‐1/TMBIM6) is the founding member of the evolutionary conserved TMBIM superfamily of proteins that share sequence homology within the transmembrane Bax inhibitor‐containing motif (TMBIM). Mechanistically, BI‐1/TMBIM6 and all the other mammalian TMBIM proteins appear to be involved in the maintenance of calcium homeostasis, and the crystal structure of a bacterial TMBIM protein, BsYetJ, suggests that the protein is a pH‐sensitive calcium leak. The budding yeast, Saccharomyces cerevisiae, has a single TMBIM family member (YNL305C) named Bxi1p/Ybh3p. To determine the function of Bxi1p/Ybh3p, we overexpressed Bxi1p‐EGFP in E. coli to determine if it is a calcium channel. We show that bacterial cells expressing Bxi1p‐EGFP are more permeable to calcium than controls. Thus, our data suggests that yeast Bax inhibitor (Bxi1p) is a calcium channel in E. coli, lending support to our proposal that Bxi1p is a bona fide member of the TMBIM family of proteins. Further, we use our bacterial system to show that gadolinium is an inhibitor of Bxi1p in vivo, suggesting a path forward to identifying other small‐molecular inhibitors of this clinically‐important and highly conserved superfamily of proteins. Finally, parallel experiments revealed that the human Bax Inhibitor‐1 (HsBI‐1/TMBIM6) is also a calcium channel in bacteria that can be inhibited by gadolinium. Support or Funding Information Our laboratory is supported by grant NIGMS R15 GM110578, awarded to N. Austriaco.