Structural and dynamical insights into SilE silver binding from combined analytical probes

Area of Science:

• Biochemistry
• Microbiology
• Structural Biology

Background:

• Silver's historical use as an antimicrobial is challenged by emerging bacterial resistance.
• The sil operon confers silver resistance in Gram-negative bacteria, with SilE protein playing a critical role.
• Previous understanding depicted SilE as intrinsically disordered, folding upon silver binding.

Purpose of the Study:

• To elucidate the structural characteristics of SilE in the presence of silver ions.
• To identify silver binding sites and conformational dynamics of SilE.
• To understand SilE's role in bacterial silver resistance mechanisms.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy
• Circular Dichroism (CD)
• Small-Angle X-ray Scattering (SAXS)
• High-Resolution Mass Spectrometry (HRMS)
• Capillary Electrophoresis-Inductively Coupled Plasma Mass Spectrometry (CE-ICP-MS)
• Ion Mobility Mass Spectrometry (IM-MS)

Main Results:

• SilE exhibits four distinct helical segments upon binding silver ions.
• Four high-affinity silver binding sites were identified within SilE.
• SilE displays significant conformational flexibility, sampling diverse structures from elongated to compact forms.
• This flexibility enhances the accessibility of histidine and methionine residues crucial for silver binding.

Conclusions:

• SilE is not a simple intrinsically disordered protein but a flexible structure with defined helical regions upon silver binding.
• The identified structural features and binding sites provide critical insights into SilE's function in silver resistance.
• These findings pave the way for designing novel inhibitors to combat silver-resistant bacteria.