Fig. 1. FKBP8 is a widely expressed integral membrane protein. (A) Domain structure of murine FKBP8. Numbers on top indicate positions of amino acid residues. N is the N-terminal sequence missing in previous literature; PPI (residues 110-194), TPR (262-329) and the transmembrane domain (M; 381-400) are marked. (B) Immunoblots of mouse tissue homogenates. (C) FKBP8 is solubilized only with a detergent. TGN38, a known integral membrane protein shown here as a control. (D) Left, immunoblotting analyses of in vitro translated FKBP8 in the presence or absence of membranes. Middle, protease protection assay to determine membrane topography. FKBP8 was not protected by intact membranes. By comparison, the ER luminal protein BiP was fully protected. Right, a schematic diagram showing FKBP8 situated outside of the ER lumen. (E) FKBP8 is localized in the mitochondria of cultured fibroblasts (left), as shown by overlapping staining patterns of FKBP8 (red) and MitoTracker (green). Scale bar: 10 µm.