(9DDM)</scene>
The cryo-EM structure of the TolA–TolQ–TolR complex was obtained after removing the flexible periplasmic portion of TolA which created heterogeneity. This removal was done via a TEV-cleavable construct. The resulting assembly has a 5:2:2 TolQ:TolR:TolA stoichiometry. TolQ forms a pentameric scaffold of seven α-helices per subunit, including three tilted transmembrane helices shaped by conserved proline-induced kinks (). TolR forms a dimer within the central hydrophobic pore, with its essential residue Asp23 positioned near a ring of TolQ Thr138/Thr178, creating a proton-linked polar gate. Two TolA transmembrane helices bind peripherally through the conserved SHLS motif, with His22 making key contacts with TolQ. The cytoplasmic domain of TolQ helices are intrinsically flexible showing dynamic nature during pmf driven activities
Structure of the E. coliTonB–ExbBD Complex
The E. coli TonB–ExbBD complex is a 1:5:2 assembly in which five ExbB subunits form a tilted-helix pentameric scaffold that encloses a parallel but axially offset dimer of ExbD transmembrane helices. The ExbB pentamer generates a hydrophobic central pore into which the ExbD TM dimer inserts, while the N-terminal cytoplasmic domains of ExbD form an asymmetric pair stabilized by conserved ExbB residues. The TonB forms a single transmembrane helix with a conserved SHLS motif. The transmembrane helix is tilted ~15° in the membrane and interacts with the ExbB through conserved TonB Ser16 and His20. The complex also contains tightly bound phosphatidylethanolamine lipids at ExbB subunit interfaces.
References
Celia, H., Botos, I., Ghirlando, R., Duché, D., Beach, B. M., Lloubes, R., & Buchanan, S. K. (2025). Cryo-EM structures of the E. coli Ton and Tol motor complexes. Nature Communications, 16, 5506. [1](https://doi.org/10.1038/s41467-025-61286-z)
About this Page
This page was created by Niranjana Vinod.
University/Institution Name (Indian Institute of Science Education and Research,Pune)
</StructureSection>
