Neutralization Mechanism of a HipA-like Toxin Targeting Isoleucyl-tRNA Synthetase

Area of Science:

• Bacterial Toxin-Antitoxin Systems
• Molecular Biology
• Structural Biology

Background:

• Toxin-antitoxin (TA) systems regulate bacterial growth and survival.
• The HipBA system is a type II TA system with a HipA toxin and HipB antitoxin.
• Structural and functional diversity of HipBA-like systems is not well understood.

Purpose of the Study:

• Investigate the HipBA-like module from Pseudomonas fluorescens (HipBA_Pf).
• Elucidate the structural and functional roles of the HipB_Pf C-terminal region in HipA_Pf neutralization.
• Identify the specific molecular target of HipA_Pf.

Main Methods:

• X-ray crystallography
• AlphaFold modeling
• Mutagenesis assays

Main Results:

• The HipB_Pf C-terminal region forms two α-helices upon binding HipA_Pf, crucial for neutralization.
• HipB_Pf binding inhibits HipA_Pf by blocking ATP binding sites, potentially via conformational changes.
• HipA_Pf phosphorylates isoleucyl-tRNA synthetase at Ser604, inhibiting its aminoacylation activity.

Conclusions:

• The HipB_Pf C-terminal region is critical for toxin binding and neutralization.
• HipA_Pf exhibits divergent substrate specificity compared to other HipA toxins.
• Understanding HipBA_Pf provides insights into TA system diversity and bacterial growth regulation.