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ExbD mutants define initial stages in TonB energization.

Anne A Ollis¹, Kathleen Postle

¹Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.

Journal of Molecular Biology

|November 22, 2011

Summary

This summary is machine-generated.

The Escherichia coli TonB system uses ExbB and ExbD proteins to link proton energy to TonB, enabling nutrient transport. This study reveals three stages of TonB energization, showing how proton motive force and ExbD regulate TonB

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Area of Science:

Microbiology
Biochemistry
Molecular Biology

Background:

The TonB system in Escherichia coli is crucial for nutrient uptake via outer membrane transporters.
ExbB and ExbD proteins are known to couple proton motive force (pmf) to TonB for energy transduction.
ExbD is hypothesized to mediate conformational changes in TonB during this energy transfer process.

Purpose of the Study:

To investigate the role of ExbD mutants and pmf variations in modulating TonB's conformational state.
To elucidate the mechanism by which ExbD facilitates energy transduction within the TonB system.
To characterize the distinct stages of TonB energization in vivo.

Main Methods:

Utilized Escherichia coli spheroplasts as an in vivo system to study protein interactions and conformational changes.
Examined TonB proteinase K sensitivity under varying conditions of ExbD mutations and pmf.
Investigated the formation of pmf-dependent formaldehyde cross-links between TonB and ExbD periplasmic domains.

Main Results:

Identified three distinct stages of TonB energization, characterized by differential proteinase K sensitivity and cross-linking.
Demonstrated that specific ExbD mutations (L123Q, D25N) and protonophores disrupt or alter TonB energization and interaction with ExbD.
Showed that pmf availability toggles TonB between distinct conformational states (Stage II and Stage III), which are interdependent with ExbD conformational changes.

Conclusions:

ExbD acts as a key coupling component, linking proton motive force to TonB.
Conformational changes in both ExbD and TonB periplasmic domains are critical for energy transduction.
The study supports a model where ExbD facilitates transitions between unenergized and energized states of TonB-ExbD heterodimers.