Functional domains of colicin M

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Colicin M is a bacteriocin produced by Escherichia coli that inhibits protein synthesis.
• Colicin M utilizes specific outer membrane receptors for cell entry.
• Understanding colicin M's structure-function relationship is key to its mechanism of action.

Purpose of the Study:

• To elucidate the functional domain organization of colicin M.
• To identify the regions responsible for receptor binding and cytotoxic activity.
• To investigate the role of the carboxy-terminal sequence in colicin M function.

Main Methods:

• Proteolytic digestion to isolate functional fragments.
• Binding assays to assess receptor interaction.
• Cell viability assays to determine cytotoxic activity.
• Amino acid sequencing of the N-terminus and C-terminus.

Main Results:

• A 24,000 Mr carboxy-terminal fragment of colicin M was isolated.
• This fragment bound to the outer membrane receptor and inhibited colicin M and phage T5.
• The fragment exhibited cell-killing activity upon osmotic shock.
• The carboxy-terminal Lys-Arg sequence was essential for activity, with its removal leading to inactivation.

Conclusions:

• The isolated fragment contains both the receptor binding site and the active center of colicin M.
• The carboxy-terminal domain is critical for colicin M's cytotoxic function.
• A specific sequence is required for colicin M transport into the cell, which is absent in the isolated fragment.