Degradation of Components of the Lpt Transenvelope Machinery Reveals LPS-Dependent Lpt Complex Stability in <i>Escherichia coli</i>.


Lipopolysaccharide (LPS) is a peculiar component of the outer membrane (OM) of many Gram-negative bacteria that renders these bacteria highly impermeable to many toxic molecules, including antibiotics. LPS is assembled at the OM by a dedicated intermembrane transport system, the Lpt (LPS transport) machinery, composed of seven essential proteins located in the inner membrane (IM) (LptB2CFG), periplasm (LptA), and OM (LptDE). Defects in LPS transport compromise LPS insertion and assembly at the OM and result in an overall modification of the cell envelope and its permeability barrier properties. LptA is a key component of the Lpt machine. It connects the IM and OM sub-complexes by interacting with the IM protein LptC and the OM protein LptD, thus enabling the LPS transport across the periplasm. Defects in Lpt system assembly result in LptA degradation whose stability can be considered a marker of an improperly assembled Lpt system. Indeed, LptA recruitment by its IM and OM docking sites requires correct maturation of the LptB2CFG and LptDE sub-complexes, respectively. These quality control checkpoints are crucial to avoid LPS mistargeting. To further dissect the requirements for the complete Lpt transenvelope bridge assembly, we explored the importance of LPS presence by blocking its synthesis using an inhibitor compound. Here, we found that the interruption of LPS synthesis results in the degradation of both LptA and LptD, suggesting that, in the absence of the LPS substrate, the stability of the Lpt complex is compromised. Under these conditions, DegP, a major chaperone-protease in Escherichia coli, is responsible for LptD but not LptA degradation. Importantly, LptD and LptA stability is not affected by stressors disturbing the integrity of LPS or peptidoglycan layers, further supporting the notion that the LPS substrate is fundamental to keeping the Lpt transenvelope complex assembled and that LptA and LptD play a major role in the stability of the Lpt system.





Published Version (Please cite this version)


Publication Info

Martorana, Alessandra M, Elisabete CCM Moura, Paola Sperandeo, Flavia Di Vincenzo, Xiaofei Liang, Eric Toone, Pei Zhou, Alessandra Polissi, et al. (2021). Degradation of Components of the Lpt Transenvelope Machinery Reveals LPS-Dependent Lpt Complex Stability in Escherichia coli. Frontiers in molecular biosciences, 8. p. 758228. 10.3389/fmolb.2021.758228 Retrieved from

This is constructed from limited available data and may be imprecise. To cite this article, please review & use the official citation provided by the journal.



Eric John Toone

Professor Emeritus of Chemistry

Dr. Toone is a physical organic chemist who studies relationships between structure and activity in the context of biology. Currently active programs exist in biocatalysis/applied enzymology, ligand binding and the activity of water, and the synthesis of novel donors of nitric oxide. The study of these problems makes use of synthetic organic chemistry, traditional enzymology, isothermal titration microcalorimetry, and the techniques of directed evolution.


Pei Zhou

Professor of Biochemistry

The Zhou lab focuses on the elucidation of the structure and dynamics of protein–protein and protein–ligand interactions and their functions in various cellular processes. Our current efforts are directed at enzymes and protein complexes involved in bacterial membrane biosynthesis, translesion DNA synthesis, co-transcriptional regulation, and host-pathogen interactions. Our investigations of these important cellular machineries have led to the development of novel antibiotics and cancer therapeutics, as well as the establishment of new biotechnology adventures.


The Zhou lab integrates a variety of biochemical and biophysical tools, including NMR, X-ray crystallography, cryo-EM, and enzymology. The lab has played a major role in the development and application of innovative NMR technologies, including high-resolution, high-dimensional spectral reconstruction techniques.

Unless otherwise indicated, scholarly articles published by Duke faculty members are made available here with a CC-BY-NC (Creative Commons Attribution Non-Commercial) license, as enabled by the Duke Open Access Policy. If you wish to use the materials in ways not already permitted under CC-BY-NC, please consult the copyright owner. Other materials are made available here through the author’s grant of a non-exclusive license to make their work openly accessible.