Mapping functional domains of colicin M

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Colicin M (Cma) is a bacteriocin that lyses Escherichia coli cells.
• Cma inhibits murein biosynthesis by hydrolyzing a specific phosphate ester in the periplasm.

Purpose of the Study:

• To identify functional domains of Colicin M (Cma) responsible for its activity and uptake.
• To elucidate the molecular mechanism of Cma-mediated cell lysis.

Main Methods:

• Isolation and characterization of 54 point and deletion mutants of Cma.
• Distinguishing activity and uptake mutants using osmotic shock.
• Assessing Cma's interaction with the FhuA receptor and Ton system.

Main Results:

• Deletion of hydrophobic helix α1 abolished FhuA binding, identifying it as the receptor-binding site.
• C-terminal Lys-Arg deletion reduced Cma translocation across the outer membrane.
• Asp226 and surrounding residues were identified as critical for the active site's catalytic function.

Conclusions:

• Specific regions of Cma are essential for receptor binding, translocation, and catalytic activity.
• The findings support a three-domain model for Cma structure and function.
• Asp226 is proposed to be directly involved in the hydrolysis of the phosphate ester in murein biosynthesis.