1.B.33.2.4
TamA (YftM) of 577 aas; has a 16 transmembrane β-stranded β-barrel with 3 PORTRA domains.  The 2.3 Å crystal structure is known revealing that the barrel is closed by a lid-loop (Gruss et al. 2013).  The C-terminal β-strand of the barrel forms an unusual inward kink, which weakens the lateral barrel wall and creates a gate for substrate access to the lipid bilayer.  TamA is an Omp85 homologue that may function in autotransporter biogenesis together with TamB (TC# 1.B.22.1.2) and OMP85 (Selkrig et al. 2012). The TAM complex 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 (Heinz et al. 2015). Possibly TamB nucleates folding of the passenger domain while TamA/B-BamA interact to catalyze β-domain membrane insertion and pore enlargement to facilitate translocation of partially folded autotransporters (M. Babu et al., unpublished hypothesis).