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Regulated assembly of the transenvelope protein complex required for lipopolysaccharide export
Elizaveta Freinkman1, Suguru Okuda, Natividad Ruiz
1Chemical Biology Graduate Program, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA.
Biochemistry
|June 7, 2012
Summary
Researchers discovered how Gram-negative bacteria transport lipopolysaccharide (LPS) using the Lpt protein bridge. This process ensures LPS is only moved when it can reach the cell surface, preventing drug resistance issues.
Area of Science:
- Microbiology and Molecular Biology
- Bacterial Cell Envelope Structure and Function
Background:
- Gram-negative bacteria possess a protective outer membrane (OM) containing lipopolysaccharide (LPS).
- LPS biosynthesis occurs at the inner membrane, requiring a transport mechanism to reach the OM.
- The LPS transport (Lpt) proteins (LptA-G) are implicated in bridging the periplasm, but their assembly and regulation remain unclear.
Purpose of the Study:
- To elucidate the mechanism of Lpt protein bridge assembly in Gram-negative bacteria.
- To identify specific protein-protein interactions within the Lpt transport system.
- To determine the order of events in LPS transport to the outer membrane.
Main Methods:
- In vivo photo-cross-linking experiments to map protein-protein interactions.
- Analysis of Lpt protein complex formation and LPS translocon assembly.
- Investigating the sequential assembly of the transenvelope bridge.
Main Results:
- Specific protein-protein interaction sites within the Lpt bridge were identified.
- The formation of the transenvelope Lpt bridge is dependent on the prior assembly of the LPS translocon in the OM.
- An ordered assembly process ensures LPS transport only occurs when translocation across the OM is possible.
Conclusions:
- The Lpt protein complex forms a regulated bridge for LPS transport across the Gram-negative bacterial envelope.
- Outer membrane translocon assembly precedes bridge formation, establishing a quality control mechanism.
- This ordered pathway prevents LPS mistargeting and ensures its proper delivery to the cell surface.
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