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The TolB protein interacts with the porins of Escherichia coli
A Rigal1, E Bouveret, R Lloubes
1Laboratoire d'Ingénierie et de Dynamique des Macromolécules, Institut de Biologie Structurale et Microbiologie, Centre National de la Recherche Scientifique, Marseille, France.
Abstract:
TolB is a periplasmic protein of the cell envelope Tol complex. It is partially membrane associated through an interaction with the outer membrane lipoprotein PAL (peptidoglycan-associated lipoprotein), which also belongs to the Tol system. The interaction of TolB with outer membrane porins of Escherichia coli was investigated with a purified TolB derivative harboring a six-histidine tag. TolB interacted with the trimeric porins OmpF, OmpC, PhoE, and LamB but not with their denatured monomeric forms or OmpA. These interactions took place both in the presence and in the absence of lipopolysaccharide. TolA, an inner membrane component of the Tol system, also interacts with the trimeric porins via its central periplasmic domain (R. Dérouiche, M. Gavioli, H. Bénédetti, A. Prilipov, C. Lazdunski, and R. Lloubès, EMBO J. 15:6408-6415, 1996). In the presence of the purified central domain of TolA (TolAIIHis), the TolB-porin complexes disappeared to form TolAIIHis-porin complexes. These results suggest that the interactions of TolA and TolB with porins might take place in vivo and might be concomitant events participating in porin assembly. They also suggest that the Tol system as a whole may be involved in porin assembly in the outer membrane.
Insights
TolB protein interacts with trimeric outer membrane porins in Escherichia coli. This interaction, alongside TolA, suggests the Tol system is involved in porin assembly within the bacterial cell envelope.
Area of Science:
- Microbiology
- Molecular Biology
- Structural Biology
Background:
- The Tol system is crucial for bacterial cell envelope integrity and function.
- TolB is a periplasmic protein within the Tol complex, interacting with the outer membrane lipoprotein PAL.
- Outer membrane porins regulate the passage of molecules into and out of the bacterial cell.
Purpose of the Study:
- To investigate the interaction between the TolB protein and outer membrane porins of Escherichia coli.
- To elucidate the role of TolB and its interaction with TolA in porin assembly.
Main Methods:
- Purification of a TolB derivative with a six-histidine tag.
- In vitro interaction assays using purified TolB and various outer membrane porins (OmpF, OmpC, PhoE, LamB).
- Competition assays using the purified central domain of TolA (TolAIIHis).
Main Results:
- Purified TolB specifically interacted with trimeric forms of OmpF, OmpC, PhoE, and LamB, but not with denatured monomers or OmpA.
- These interactions occurred independently of lipopolysaccharide.
- The presence of TolAIIHis disrupted TolB-porin complexes, forming TolAIIHis-porin complexes, indicating a potential competitive interaction.
Conclusions:
- TolB and TolA interact with trimeric porins, suggesting these interactions are biologically relevant in vivo.
- The findings imply that TolA and TolB interactions with porins may be simultaneous events during porin assembly.
- The study proposes that the entire Tol system plays a role in the assembly of porins in the outer membrane.