Structure of the atypical bacteriocin pectocin M2 implies a novel mechanism of protein uptake

Area of Science:

• Microbiology
• Structural Biology
• Protein Engineering

Background:

• Colicin-like bacteriocins are protein antibiotics effective against Gram-negative bacteria.
• These bacteriocins utilize nutrient uptake systems to cross the outer bacterial membrane.
• Pectobacterium spp. are plant pathogens that rely on iron acquisition.

Purpose of the Study:

• To structurally characterize pectocin M2, a colicin M-like bacteriocin active against Pectobacterium.
• To elucidate the mechanism of outer membrane translocation for pectocin M2.
• To identify novel bacteriocins and their delivery mechanisms in Pectobacterium.

Main Methods:

• X-ray crystallography was used to determine the structure of pectocin M2.
• Solution-state conformational analysis was performed using biophysical techniques.
• Bioinformatic analysis was employed to identify homologous bacteriocins and domains.

Main Results:

• Pectocin M2 lacks the typical unstructured translocation domain, featuring a ferredoxin domain linked to its cytotoxic domain by an alpha-helix.
• The ferredoxin domain of pectocin M2 mimics plant ferredoxins, enabling it to hijack the Pectobacterium iron uptake system.
• A new bacteriocin, pectocin P, was identified, featuring a ferredoxin delivery module and a lysozyme-like cytotoxic domain.

Conclusions:

• The ferredoxin domain serves as a versatile delivery module for cytotoxic payloads in Pectobacterium bacteriocins.
• Pectocin M2 represents a unique class of bacteriocins with a distinct mechanism for outer membrane translocation.
• Understanding these bacteriocin-host interactions provides insights into bacterial pathogenesis and antibiotic development.