title: Evolution of the Translocation and Assembly Module (TAM).
abstract: Bacterial outer membrane proteins require the beta-barrel assembly machinery (BAM) for their correct folding and function. The central component of this machinery is BamA, an Omp85 protein that is essential and found in all Gram-negative bacteria. An additional feature of the BAM is the translocation and assembly module (TAM), comprised TamA (an Omp85 family protein) and TamB. We report that TamA and a closely related protein TamL are confined almost exclusively to Proteobacteria and Bacteroidetes/Chlorobi respectively, whereas TamB is widely distributed across the majority of Gram-negative bacterial lineages. A comprehensive phylogenetic and secondary structure analysis of the TamB protein family revealed that TamB was present very early in the evolution of bacteria. Several sequence characteristics were discovered to define the TamB protein family: A signal-anchor linkage to the inner membrane, beta-helical structure, conserved domain architecture and a C-terminal region that mimics outer membrane protein beta-strands. Taken together, the structural and phylogenetic analyses suggest that the TAM likely evolved from an original combination of BamA and TamB, with a later gene duplication event of BamA, giving rise to an additional Omp85 sequence that evolved to be TamA in Proteobacteria and TamL in Bacteroidetes/Chlorobi.
authors.affiliation: Department of Microbiology, Monash University, Melbourne, Victoria, Australia.
authors.forename: Eva
authors.initials: E
authors.lastname: Heinz
authors.affiliation: Department of Biochemistry & Molecular Biology, Monash University, Melbourne, Victoria, Australia Present address: European Molecular Biology Laboratory, Genome Biology Unit, Heidelberg, Germany.
authors.forename: Joel
authors.initials: J
authors.lastname: Selkrig
authors.affiliation: Department of Microbiology, Monash University, Melbourne, Victoria, Australia.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Belousoff
authors.affiliation: Department of Microbiology, Monash University, Melbourne, Victoria, Australia trevor.lithgow@monash.edu.
authors.forename: Trevor
authors.initials: T
authors.lastname: Lithgow
mesh_terms: D020816:Amino Acid Motifs; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000145:classification / Q000235:genetics*; D041963:Bacteroidetes / Q000235:genetics; D019143:Evolution, Molecular; D014644:Genetic Variation; D005810:Multigene Family; D010802:Phylogeny; D020560:Proteobacteria / Q000235:genetics
chemical_list: D001425:Bacterial Outer Membrane Proteins
keywords: TamA; TamB; beta-barrel assembly; membrane biogenesis; outer membrane; translocation