Fig. 4: The structure of the TolA-TolB complex suggests a role in force transduction. | Nature Communications

Fig. 4: The structure of the TolA-TolB complex suggests a role in force transduction.

From: The lipoprotein Pal stabilises the bacterial outer membrane during constriction by a mobilisation-and-capture mechanism

Fig. 4

a Average distribution of Pal-mCherry along the normalized x-axis of E. coli cells expressing mutant TolB from its native locus. Deletion of TolB’s N-terminus (residues 22−33) abolishes Pal-mCherry accumulation at the septum. The curve is an average from 30 cells, with shaded area representing standard deviation. Below: representative TIRFM and brightfield images of cells. Scale bar, 1 µm. b Solution-state NMR structure of the C-terminal domain of TolA (residues 224−347, beige) in complex with the N-terminus of TolB (the TolA box; residues 22ADPLVISSGNDRA34; red) from P. aeruginosa. See Supplementary Table 1 for full list of NMR restraints and refinement statistics. The first 23 residues of TolA (224−247) are unstructured in this complex and are not represented in the figure. Left-hand panel, overlay of the 20 lowest energy structures for the complex. Pairwise root mean squared deviation (RMSD) for the ensemble was 1.03 ± 0.12 Å. Right-hand panel, average ensemble structure for the complex. TolB22–34 binds by β-strand augmentation, forming a parallel β-strand with TolA. c TolB22–34, stick representation, binds to a cleft on the TolA surface. Hydrophobic residues in TolB play a prominent role in stabilising the complex (in particular Leu25, Val26 and Ile27). Source data are provided as a Source Data file. d β-strand augmentation is at the heart of both Ton and Tol complexes. The figure shows a comparison of a TonB-TBDT complex71 with TolA-TolB (present work). Complex formation in both cases requires a C-terminal element of secondary structure be displaced in order for a parallel β-strand to form. A structural overlay of the resulting complexes has an rmsd of 2.2 Å. e Alanine-substitution of the three key hydrophobic residues in E. coli TolB (Ile25Ala, Val26Ala, Ile27Ala; TolBAAA) abolishes Pal-mCherry accumulation at the septum of dividing cells. The fluorescence distribution shown is an average from 30 cells, with shaded area depicting standard deviation. Representative TIRFM and brightfield images of cells are shown below the fluorescence data. Scale bar, 1 µm. Source data are provided as a Source Data file.

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