Figure 1. Selective pressure has maintained specific residues in TamA through the course of evolution.

(a) Topology of TamA and TamB, spanning the bacterial outer membrane (OM) and inner membrane (IM). The TAM drives the insertion of substrate proteins (blue) such as Ag43 into the membrane⁴,¹⁴. Rate4Site analysis of TamA sequences (detailed in Supplementary Table 1) plotted onto the structural coordinates of TamA (pdb 4C00). The crenel in the β-barrel domain between the first and last β-strands is indicated with an arrow; POTRA domains are labeled P1, P2 and P3. (b) POTRA domain sequences from TamA and BamA of representative species (Supplementary Table 2) were extracted and subjected to CLANS¹⁹. Lines are shown connecting similar sequences with an P-value cut-off of 1e-2. Sequences derived from each POTRA domain form a distinct group, color-coded for the corresponding three TamA POTRA domains and the five BamA POTRA domains. (c) Representation of the LSQ fits between TamA POTRA 1 (green) and TamA POTRA 2 (cyan) and the BamA POTRA 1 (yellow) and BamA POTRA2 (orange), calculated using PyMOL (www.pymol.com/pymol). A complete comparison is shown in Supplementary Figure 2.