Neutralization mechanism of a HipA-like toxin targeting isoleucyl-tRNA synthetase

ABSTRACT: HipAB is a type II toxin-antitoxin (TA) system that targets and inactivates specific aminoacyl-tRNA synthetases in response to various stresses. While the molecular targets and neutralization mechanisms of several HipAB-like TA systems have been well characterized, their structural and functional diversity remains less understood. In this study, we investigated a HipAB-like module (HipABpf) from Pseudomonas fluorescens, where the HipBpf antitoxin features a long, disordered C-terminal region in the absence of HipApf. Using a combination of X-ray crystallography, AlphaFold modeling and mutagenesis assays, we show that upon binding to HipApf, part of this C-terminal region forms two α-helices that are essential for both the interaction with and neutralization of the HipApf toxin. Importantly, HipBpf binding blocks the ATP binding sites of HipApf, potentially by inducing a conformational change in the HipApf N1 subdomain via its C-terminal α6 helix. We also discovered that HipApf phosphorylates the isoleucyl-tRNA synthetase at Ser604, strongly inhibiting its aminoacylation activity. Finally, we demonstrated that the HipABpf system plays a role in coping with oxidative stress and carbon starvation. Taken together, our findings reveal the critical role of the HipBpf C-terminal region in toxin binding and neutralization, while also highlighting the evolutionarily divergent substrate preferences of HipA-like toxins.

ORGANISM(S): Escherichia Coli K-12

SUBMITTER: Yongxing He  

PROVIDER: PXD062828 | iProX | Fri Apr 11 00:00:00 BST 2025

REPOSITORIES: iProX