Human FAM173B is an evolutionarily conserved mitochondrial protein.
A, phylogram of FAM173-like proteins. The tree encompasses FAM173A (blue) and FAM173B (red) proteins from the vertebrates Homo sapiens (Hs), Mus musculus (Mm), Xenopus laevis (Xl), Salmo salar (Ss), Danio rerio (Dr), and Gallus gallus (Gg), as well as FAM173-like proteins from the nonvertebrate animals (green) Capitella teleta (Cte), C. elegans (Cel), Tribolium castaneum (Tca), Daphnia pulex (Dpu), Apis mellifera (Ame), Drosophila melanogaster (Dme), Aedes aegypti (Aae), and Hydra vulgaris (Hvu). Also included are various crenarchaeal homologues (purple), including the previously characterized aKMT enzyme from Sulfolobus islandicus (Sis) and corresponding homologues from Pyrolobus fumarii (Pfu), Hyperthermus butylicus (Hbu), Ignicoccus islandicus (Iis), Staphylothermus hellenicus (She), and Methanobacterium formicicum (Mfo), as well as the bacterial aKMT-like enzymes (brown) from Pseudomonas stutzeri (Pst), Salinibacter ruber (Sru), Rhodopseudomonas palustris (Rpa), and Agrobacterium (multispecies) (Agr). Accession numbers of used sequences are given in Table S1. B, sequence elements of the N-terminal portion of FAM173B and alignment of the N-terminal part of putative FAM173 orthologues from organisms denoted as in A. Colors indicate the position of nonconserved NTS (gray), predicted TMD (yellow), conserved preMT (orange), and N-terminal fragment of the MTase domain (green). Hallmark motifs of the 7BS MTase domain are indicated by black boxes. The position of the conserved acidic residue in motif Post I (Glu-117 in H. sapiens FAM173B), crucial for AdoMet binding, is marked with an asterisk. C, subcellular localization of FAM173B-derived GFP fusion proteins. A schematic representation of the used FAM173B-derived sequences is given (top), with the various domains denoted as in B. Shown are confocal fluorescence microscopy images of HeLa cells, fixed 24 h after transient transfection with plasmids encoding FAM173B-GFP, (Δ55)-FAM173B-GFP, or (56–90)-FAM173B-GFP. Cells were counterstained with anti-COX IV primary antibody, followed by Alexa Fluor 568–conjugated secondary antibody, to visualize the mitochondria, and with DAPI, to visualize the nuclei. Data were acquired through green (GFP), red (COX IV), and blue (DAPI) channels and merged.