Structural and functional properties of colicin M

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Colicins are bacteriocins produced by bacteria, including Escherichia coli, that exhibit antimicrobial activity against related strains.
• Colicin M is a specific type of colicin known to lyse sensitive E. coli cells, but its precise mechanism and inactivation have been areas of investigation.

Purpose of the Study:

• To isolate and characterize Colicin M from Escherichia coli Cl139.
• To investigate the mechanism of cell lysis induced by Colicin M, including its dependence on time, calcium ions, and inactivation by external agents.
• To determine the conditions under which Colicin M's activity can be reversed.

Main Methods:

• Isolation and purification of Colicin M.
• Determination of molecular weight using SDS-PAGE.
• Time-course experiments to assess lysis and rescue kinetics.
• Treatment with trypsin and sodium dodecyl sulfate (SDS) to evaluate colicin inactivation.
• Use of calcium ions (Ca2+) and ethylene glycol-bis(beta-aminoethyl ether)-N,N'-tetraacetate (EGTA) to study rescue mechanisms.

Main Results:

• Colicin M was isolated as a single polypeptide with a molecular weight of 27,000 +/- 2,000.
• Continuous action of Colicin M for 20 minutes was required for cell lysis.
• Colicin M was resistant to trypsin unless adsorbed to cells, and could be inactivated by trypsin or SDS within 4-5 minutes.
• Cell killing by Colicin M necessitated Ca2+ ions.
• Cells could be rescued by EGTA immediately before lysis, rendering bound Colicin M sensitive to trypsin again.

Conclusions:

• Colicin M requires sustained interaction and Ca2+ ions for its bactericidal activity.
• The cell surface undergoes changes during colicin action, affecting colicin accessibility to inactivating agents.
• EGTA chelation of Ca2+ ions can reverse the effect of Colicin M, suggesting a reversible binding or conformational change at the cell surface.