Functional association of cell death suppressor, Arabidopsis Bax inhibitor‐1, with fatty acid 2‐hydroxylation through cytochrome b5
2009
Nagano, Minoru | Ihara‐Ohori, Yuri | Imai, Hiroyuki | Inada, Noriko | Fujimoto, Masaru | Tsutsumi, Nobuhiro | Uchimiya, Hirofumi | Kawai‐Yamada, Maki
Bax inhibitor‐1 (BI‐1) is a widely conserved cytoprotective protein localized in the endoplasmic reticulum (ER) membrane. We identified Arabidopsis cytochrome b5 (AtCb5) as an interactor of Arabidopsis BI‐1 (AtBI‐1) by screening the Arabidopsis cDNA library with the split‐ubiquitin yeast two‐hybrid (suY2H) system. Cb5 is an electron transfer protein localized mainly in the ER membrane. In addition, a bimolecular fluorescence complementation (BiFC) assay and fluorescence resonance energy transfer (FRET) analysis confirmed that AtBI‐1 interacted with AtCb5 in plants. On the other hand, we found that the AtBI‐1‐mediated suppression of cell death in yeast requires Saccharomyces cerevisiae fatty acid hydroxylase 1 (ScFAH1), which had a Cb5‐like domain at the N terminus and interacted with AtBI‐1. ScFAH1 is a sphingolipid fatty acid 2‐hydroxylase localized in the ER membrane. In contrast, AtFAH1 and AtFAH2, which are functional ScFAH1 homologues in Arabidopsis, had no Cb5‐like domain, and instead interacted with AtCb5 in plants. These results suggest that AtBI‐1 interacts with AtFAHs via AtCb5 in plant cells. Furthermore, the overexpression of AtBI‐1 increased the level of 2‐hydroxy fatty acids in Arabidopsis, indicating that AtBI‐1 is involved in fatty acid 2‐hydroxylation.
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