Directed evolution of SecB chaperones toward toxin-antitoxin systems

Area of Science:

• Microbiology
• Molecular Biology
• Protein Folding

Background:

• SecB chaperones are crucial for bacterial protein export.
• Some SecB family members have specialized in regulating toxin-antitoxin (TA) systems, which aid bacterial stress adaptation and persistence.
• Tripartite TA-chaperone (TAC) systems involve a chaperone assisting antitoxin folding and preventing its degradation to inhibit toxin activity.

Purpose of the Study:

• To investigate how generalist chaperones like SecB can specialize in regulating TA systems.
• To understand the molecular mechanisms underlying chaperone specialization in TAC systems.

Main Methods:

• Utilized the export chaperone SecB from Escherichia coli and the TAC system from Mycobacterium tuberculosis as model systems.
• Employed directed evolution techniques to identify mutations in SecB that confer specificity for TA system control.
• Characterized the functional impact of identified mutations on both TA system regulation and general protein export.

Main Results:

• Identified specific mutations in SecB that enhance its ability to regulate the model TA system.
• Demonstrated that these specialized SecB variants retain their native function in protein export.
• Highlighted the adaptability of the SecB chaperone's substrate-binding surface.

Conclusions:

• Generic chaperones possess remarkable plasticity, allowing for specialization towards specific client interactions, such as those in TA systems.
• The substrate-binding surface of chaperones can be readily remodeled through evolutionary processes to accommodate new functions.
• This adaptability in chaperones has significant implications for understanding bacterial adaptation and persistence mechanisms.