Evolution of the Translocation and Assembly Module (TAM).
Bottom Line: Bacterial outer membrane proteins require the beta-barrel assembly machinery (BAM) for their correct folding and function.An additional feature of the BAM is the translocation and assembly module (TAM), comprised TamA (an Omp85 family protein) and TamB.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.
Affiliation: Department of Microbiology, Monash University, Melbourne, Victoria, Australia.Show MeSH
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Mentions: Phylogenetic analysis of TamB revealed no clear correlation of the TamB proteins with respect to their presence in an operon with an Omp85 protein besides the monophyletic origin of the sequences associated with TamA or TamL (fig. 6 and supplementary fig. S8, Supplementary Material online). The chlamydial TamA–TamB operon seems to be derived through horizontal gene transfer (HGT) from the Alphaproteobacteria; this is also supported in the analysis of the Omp85 proteins (fig. 7 and supplementary fig. S9, Supplementary Material online). Although the Proteobacteria TamB forms a large monophyletic cluster (with the Chlamydiae; fig. 6 and supplementary fig. S8, Supplementary Material online), several Deltaproteobacteria and Epsilonproteobacteria cluster with the early-branching Phyla (such as Fusobacteria and Bacteroidetes); this likely HGT event is also reflected in the Omp85 sequences (Heinz and Lithgow 2014; fig. 7 and supplementary fig. S9, Supplementary Material online). The Acidobacteria and Aquificae both encode a second copy of BamA, which branches off monophyletic with TamA, indicating this to be the putative origin of the TAM (figs. 7 and 8 and supplementary fig. S9, Supplementary Material online). A consistent clustering of the early-branching Phyla including Spirochaetes, Deinococcus-Thermus, Firmicutes, and Cyanobacteria was also observed for TamB.Fig. 6.—
Affiliation: Department of Microbiology, Monash University, Melbourne, Victoria, Australia.