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In vivo evidence for TonB dimerization
Annette Sauter1, S Peter Howard, Volkmar Braun
1Mikrobiologie/Membranphysiologie, Universität Tübingen, D-72076 Tübingen, Germany.
Journal of Bacteriology
|September 18, 2003
Summary
TonB protein dimerization is crucial for energy-dependent transport in Escherichia coli. Specific mutations in TonB influence its interactions with various cellular transporters and receptors, affecting its function.
Area of Science:
- Microbiology
- Molecular Biology
- Protein Biochemistry
Background:
- TonB protein, complexed with ExbB and ExbD, is essential for outer membrane transport in Escherichia coli.
- This complex mediates ferric siderophore uptake, colicin activity, and phage infection.
- Understanding TonB's structure and function is key to deciphering these vital cellular processes.
Purpose of the Study:
- To investigate TonB dimerization and its role in protein complex formation.
- To identify key regions and residues within TonB critical for dimerization and function.
- To explore the relationship between TonB structure, dimerization, and its diverse functions.
Main Methods:
- Construction of hybrid proteins combining TonB fragments with ToxR, a known dimerizing protein.
- Assay of hybrid protein activity using a lacZ reporter system under the ctx promoter.
- Site-directed mutagenesis and phenotypic analysis of TonB mutants in various transport and infection assays.
Main Results:
- TonB dimerization was confirmed and found to be influenced, but not solely dependent, on ExbB and ExbD.
- The N-terminal cytoplasmic membrane anchor and C-terminal regions of TonB are important for dimer formation.
- Specific C-terminal mutations (Y163C, V188E, R204C, F230V) altered TonB's activity in a function-dependent manner, indicating specificity in interactions.
Conclusions:
- TonB dimerization is a key aspect of its function, influenced by but independent of ExbB/ExbD.
- The C-terminal region of TonB plays a critical role in mediating interactions with different TonB-dependent systems.
- Mutations in TonB can lead to specific functional defects, highlighting the intricate relationship between protein structure and diverse biological activities.