Ton-dependent colicins and microcins: modular design and evolution

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Ton-dependent colicins and microcins are actively transported into bacterial cells.
• This import process is energy-dependent, utilizing the proton motive force across the cytoplasmic membrane.
• The Ton system, comprising TonB, ExbB, and ExbD proteins, is essential for this uptake.

Purpose of the Study:

• To investigate the mechanisms of Ton-dependent colicin and microcin import.
• To understand the role of the TonB box in colicin uptake.
• To explore the processing and export of TonB-dependent microcins.

Main Methods:

• Analysis of colicin and microcin structures and their interaction with outer membrane transport proteins.
• Mutational analysis of the TonB box in colicins.
• Characterization of TonB-dependent microcin processing and export pathways.

Main Results:

• Colicins and outer membrane transporters possess a TonB box crucial for TonB interaction and uptake.
• Microcins lack a TonB box, suggesting alternative interaction mechanisms.
• Six TonB-dependent microcins with varying structures are processed and exported by homologous proteins.
• Three microcins share specificity for catecholate siderophore receptors and undergo unknown modifications.

Conclusions:

• The Ton system is central to the energy-dependent uptake of colicins and microcins.
• The TonB box is a key determinant for colicin import, but absent in microcins.
• Microcins exhibit diverse structures and processing pathways, with some linked to siderophore receptor specificity.