Export of Diverse and Bioactive Small Proteins through a Type I Secretion System

Area of Science:

• Microbiology and Molecular Biology
• Protein Secretion Systems
• Bacterial Genetics

Background:

• Small proteins have diverse biological functions, but simple systems for their secretion from Gram-negative bacteria are lacking.
• Microcins are small antibacterial proteins exported via type I secretion systems (T1SSs) in a single step.
• Substrate requirements for microcin T1SSs are not well understood.

Purpose of the Study:

• To investigate the substrate scope of the prototypic microcin V T1SS from Escherichia coli.
• To determine the limitations and potential applications of this secretion system for diverse small proteins.
• To assess the functionality of the microcin V T1SS in other Gram-negative species.

Main Methods:

• Investigated the export of various natural and synthetic small proteins using the microcin V T1SS.
• Analyzed secretion efficiency in relation to cargo protein properties, focusing on length and chemical characteristics.
• Tested the functionality of the microcin V T1SS in different Gram-negative bacterial species.

Main Results:

• The microcin V T1SS demonstrated a remarkably broad cargo capacity, exporting a wide range of small proteins.
• Secretion was largely independent of cargo protein's chemical properties, primarily constrained by protein length.
• Diverse bioactive proteins, including an antibacterial peptide, signaling factor, protease inhibitor, and human hormone, were successfully secreted and functional.
• The system functioned effectively in additional Gram-negative species relevant to the gastrointestinal tract.

Conclusions:

• The microcin V T1SS exhibits highly promiscuous small-protein export capabilities.
• This system's length-dependent secretion mechanism has significant implications for native cargo capacity.
• The microcin V T1SS offers a versatile platform for small-protein research and in vivo delivery in various Gram-negative bacteria.