Structural basis for persulfide-sensing specificity in a transcriptional regulator

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• Cysteine thiol-based regulators control cellular redox homeostasis by sensing redox-active molecules.
• The specificity of these sensors for particular reactive species (e.g., reactive oxygen or sulfur species) remains largely uncharacterized.

Purpose of the Study:

• To elucidate the structural and mechanistic basis of the thiol-based transcriptional repressor SqrR's specificity.
• To investigate how SqrR detects oxidized sulfur species and regulates gene expression.

Main Methods:

• X-ray crystallography to determine the structure of SqrR in various derivatized states.
• Mass spectrometry-based kinetic profiling to analyze reaction kinetics and selectivity.
• Biochemical assays to evaluate DNA-protein interactions.

Main Results:

• SqrR exclusively reacts with oxidized sulfur species (persulfides) to form a tetrasulfide bridge.
• This tetrasulfide bridge formation inhibits SqrR's DNA binding, repressing transcription.
• Structural analysis revealed that 'structural frustration' of the disulfide form dictates persulfide selectivity.
• An uncharacterized repressor from Acinetobacter baumannii was identified as a persulfide sensor.

Conclusions:

• SqrR acts as a specific persulfide sensor, contributing to the understanding of redox regulation in bacteria.
• The findings provide a molecular mechanism for persulfide detection and its impact on transcriptional regulation.
• This research opens avenues for identifying novel persulfide sensors in other bacterial pathogens.