Bacterial gold sensing and resistance.

Area of Science:

• Environmental Microbiology
• Metallobiology
• Bacterial Toxin Resistance

Background:

• Gold ions are environmental contaminants that can enter cells via non-specific uptake.
• Bacteria like Salmonella enterica and Cupriavidus metallidurans possess defense mechanisms against toxic metal ions.
• MerR-type transcriptional regulators are key components in bacterial metal ion sensing and resistance pathways.

Purpose of the Study:

• To investigate the molecular mechanisms by which bacterial MerR-type regulators achieve selectivity for gold ions (Au(I)).
• To understand how gold-sensing proteins differentiate between gold, copper (Cu(I)), and silver (Ag(I)) ions.
• To explore the implications of gold ion selectivity for bacterial survival in metal-rich environments.

Main Methods:

• Analysis of the metal-binding sites in Au-selective MerR-type transcriptional regulators.
• Comparison of metal coordination and binding affinities between gold sensors and copper sensors (CueR).
• Investigation of promoter recognition and operator binding specificity in Salmonella using the GolS regulator.

Main Results:

• Au-selective MerR-type proteins exhibit finely tuned dithiolate metal coordination via conserved cysteine residues.
• This specific coordination lowers affinity for Cu(I) while maintaining or increasing affinity for Au(I), enabling discrimination.
• Salmonella's GolS regulator demonstrates high selectivity for Au(I) over Cu(I)/Ag(I) and distinct promoter targeting, avoiding cross-activation with CueR.

Conclusions:

• Bacterial gold-sensing proteins possess unique structural features enabling precise discrimination between toxic Au(I) and essential Cu(I) ions.
• This selectivity allows bacteria to manage gold toxicity without compromising copper homeostasis.
• The development of selective gold sensors provides a survival advantage in environments with mixed metal ion contamination.