Fig. 3. C-terminal strands anchor folded BamA to the membrane in both PE and PG. (a) Change in ΔΔG⁰_F in PC:PE (open histograms, cyan) and PC:PG (filled histograms, purple) upon Xaa → Ala substitution in BamA. Top panel: N-terminal β1–β8; bottom panel: C-terminal β9–β16. N-terminal residues are intrinsically destabilized in PE (top panel). BamA stability is substantially lowered in both PE and PG when C-terminal residues are substituted (bottom panel). Errors are derived from propagation of uncertainty (complete data in Tables S8 and S9). (b) Intrinsically stabilizing (green fills) and destabilizing (red fills) residues of BamA measured from the end-state thermodynamics in PC:PE (left) and PC:PG (right), and highlighted on the two-dimensional topology diagram of the protein. β-Strand numbers are indicated. The results of end-state thermodynamics in PC:PE (c) and PC:PG (d) are also mapped on the structure of BamA (intrinsically stabilizing: green spheres; intrinsically destabilizing: red spheres), and the residues are annotated. Intrinsically destabilizing residues (red) are localized at β2–β4, β6–β7, and β10–β11 of BamA in PC:PE, indicating a dynamic BamA in the PE-rich outer membrane. These residues enhance BamA stability in PG, indicating a more rigid barrel less suitable for its chaperoning function. Residues at the C-terminal strands (β12–β15) stabilize the β-barrel in both membranes. K⁸⁰⁸ in the last strand is intrinsically destabilizing in both membranes.