Novel type II toxin-antitoxin systems with VapD-like proteins

Area of Science:

• Microbiology
• Molecular Biology
• Evolutionary Biology

Background:

• Type II toxin-antitoxin (TA) systems are essential prokaryotic genetic elements regulating cellular processes.
• The VapD nuclease and VapX antitoxin form a TA system contributing to Haemophilus influenzae virulence.
• VapD homologs are present in various pathogens, but their evolutionary diversity remains underexplored.

Purpose of the Study:

• To investigate the diversity and evolution of VapD-like proteins and identify novel antitoxins.
• To elucidate the structural and functional mechanisms of VapD-VapW interactions.
• To understand the evolutionary implications of a toxin evolving into an antitoxin.

Main Methods:

• Bioinformatic analysis of vapD-like genes and adjacent loci.
• Sequence and structural analysis of VapD, VapW, and VapY proteins.
• Biochemical assays to determine the functional impact of VapW on VapD activity.
• Crystal structure determination of the VapD-VapW complex.

Main Results:

• Two novel antitoxin families, VapY and VapW, were identified alongside VapX.
• VapW is a catalytically inactive homolog of VapD, retaining VapD's oligomerization interface.
• The VapD-VapW complex structure reveals VapW disrupts VapD hexamerization, despite an accessible catalytic cleft.
• VapD-VapW systems induce the SOS response, indicating DNA-related cellular targets.

Conclusions:

• VapW represents a unique evolutionary trajectory where a toxin loses catalytic activity and functions as its own antitoxin.
• The VapD-VapW system provides a novel example of TA system evolution and diversification.
• Understanding these systems can offer insights into pathogen virulence and potential therapeutic targets.