Fig. 1.

—Three-dimensional structure and biological function of mitochondrial outer membrane β-barrels (MOMBBs). Six outer membrane β-barrel subfamilies have been described so far in mitochondria: The 16-stranded SAM50/TOB55, which belongs to the OMP85 family of bacterial OMBBs and is involved in the biogenesis and membrane insertion of OMBBs (Kozjak et al. 2003), and the five members of the 19-stranded OMBB family unique to mitochondria (MOMBBs) TOM40, VDAC, MDM10, ATOM, and TAC40 (Pusnik et al. 2011; Bay et al. 2012; Zarsky et al. 2012; Flinner et al. 2013; Schnarwiler et al. 2014). For those whose three-dimensional structure is known (VDAC and TOM40), the experimental structure is shown. For those whose structure was not yet experimentally determined, homology models are shown only for illustrative purposes. For that, the best templates for the reference sequences were identified with HHPred (Zimmermann et al. 2018) over the PDB70 (as of May 2018; supplementary table 1, Supplementary Material online) and the models built with SWISS-MODEL (Biasini et al. 2014) after target-template alignment with PROMALS3D (Pei and Grishin 2014). Long loops are shown in dashed cartoon lines for clarity and named Lx, where x refers to the ranking of the loop in the predicted structure.