title: Structure and evolution of mitochondrial outer membrane proteins of beta-barrel topology.
abstract: Gram-negative bacteria are the ancestors of mitochondrial organelles. Consequently, both entities contain two surrounding lipid bilayers known as the inner and outer membranes. While protein synthesis in bacteria is accomplished in the cytoplasm, mitochondria import 90-99% of their protein ensemble from the cytosol in the opposite direction. Three protein families including Sam50, VDAC and Tom40 together with Mdm10 compose the set of integral beta-barrel proteins embedded in the mitochondrial outer membrane in S. cerevisiae (MOM). The 16-stranded Sam50 protein forms part of the sorting and assembly machinery (SAM) and shows a clear evolutionary relationship to members of the bacterial Omp85 family. By contrast, the evolution of VDAC and Tom40, both adopting the same fold cannot be traced to any bacterial precursor. This finding is in agreement with the specific function of Tom40 in the TOM complex not existent in the enslaved bacterial precursor cell. Models of Tom40 and Sam50 have been developed using X-ray structures of related proteins. These models are analyzed with respect to properties such as conservation and charge distribution yielding features related to their individual functions.
authors.affiliation: Max Planck Institute of Developmental Biology, Department Protein Evolution, Spemannstr. 35, D-72076 Tübingen, Germany. Kornelius.zeth@tuebingen.mpg.de
authors.forename: Kornelius
authors.initials: K
authors.lastname: Zeth
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017124:Conserved Sequence; D019143:Evolution, Molecular; D006090:Gram-Negative Bacteria / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D033681:Mitochondrial Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics; D051336:Mitochondrial Membranes / Q000737:chemistry*; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D050994:Voltage-Dependent Anion Channels / Q000737:chemistry / Q000235:genetics
chemical_list: D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; C487333:Sam50 protein, S cerevisiae; C066555:Tom40 protein, S cerevisiae; D050994:Voltage-Dependent Anion Channels