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Crystal structure of colicin Ia
M Wiener1, D Freymann, P Ghosh
1S-964 Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448, USA.
Nature
|January 30, 1997
Summary
Colicin Ia, an ion-channel forming protein, kills bacteria by forming channels in the cell membrane. Its structure reveals distinct domains for receptor binding, outer membrane translocation, and ion channel formation.
Area of Science:
- Bacteriology
- Structural Biology
- Biochemistry
Background:
- Colicins are bacteriocins that kill target bacteria.
- Ion-channel forming colicins utilize bacterial active-transport pathways.
- These colicins form voltage-gated ion channels in the bacterial plasma membrane.
Purpose of the Study:
- To elucidate the structural basis of colicin Ia function.
- To understand how colicin Ia interacts with bacterial cells.
- To detail the mechanism of ion channel formation by colicin Ia.
Main Methods:
- X-ray crystallography to determine the structure of colicin Ia.
- Structural analysis to identify functional domains.
- Analysis of protein structure-function relationships.
Main Results:
- Colicin Ia is a 210 Å long molecule with three functional domains.
- A central domain binds to the outer-membrane receptor.
- A second domain facilitates translocation via the TonB pathway.
- A third domain forms a voltage-gated ion channel.
- Two long alpha-helices link these domains, enabling simultaneous membrane interaction.
Conclusions:
- The structure of colicin Ia explains its mechanism of bacterial cell killing.
- Distinct domains are responsible for receptor binding, outer membrane translocation, and ion channel formation.
- The molecule's architecture allows it to bridge the periplasmic space and interact with both outer and plasma membranes.