The Omp85 protein family is widely distributed across eukaryotes and bacteria. Members of this family are characterized by a membrane-embedded beta-barrel forming domain (“bacterial surface antigen”, “D15”) and a variable number of polypeptide-transport associated (POTRA) domains. An intensely studied protein of this family is BamA, the key member of the multi-protein BAM complex, which is conserved across bacteria and is responsible for the assembly of proteins into the outer membrane. Mostly based on work in Escherichia coli and Neisseria meningitidis, BamA is known to insert several essential porins, and mutants compromised in BamA function have drastic outer membrane defects. The eukaryotic members of the Omp85 family, Sam50 and Toc75, are located in mitochondria or plastids, respectively. Here, they perform similar functions to transport and insert proteins into the outer membrane of the respective organelles. In addition to the comparatively well-described BamA in bacteria and Sam50 in eukaryotes, recent analyses have shown that several taxonomic lineages have a diverse number of Omp85 proteins with so far unknown functions. First insights were provided by the finding of the newly described TAM complex (Selkrig et al 2012, Nature Struct. Mol. Biol.), which, analogous to the BAM complex also includes a member of the Omp85 family (TamA) as its central component, assists the correct folding of the autotransporter protein p1121 and potentially other members of this group of surface proteins. The additional diversity also extends to eukaryotes, where lineage-specific duplications Sam50 serve so far unknown but distinct functions (Hewitt et al, PNAS, in press). My project investigates the presence of paralogues of the different Omp85 subgroups, as well as the presence of so far undescribed subfamilies. Insights into the evolution of this protein family are being complemented by biochemical characterization of so far undescribed paralogues.