Abstract
SummaryAg+ resistance was initially found on the Salmonella enetrica serovar Typhimurium multi‐resistance plasmid pMG101 from burns patients in 1975. The putative model of Ag+ resistance, encoded by the sil operon from pMG101, involves export of Ag+ via an ATPase (SilP), an effluxer complex (SilCFBA) and a periplasmic chaperon of Ag+ (SilE). SilE is predicted to be intrinsically disordered. We tested this hypothesis using structural and biophysical studies and show that SilE is an intrinsically disordered protein in its free apo‐form but folds to a compact structure upon optimal binding to six Ag+ ions in its holo‐form. Sequence analyses and site‐directed mutagenesis established the importance of histidine and methionine containing motifs for Ag+‐binding, and identified a nucleation core that initiates Ag+‐mediated folding of SilE. We conclude that SilE is a molecular sponge for absorbing metal ions.
Highlights
Silver is a soft, shiny, lustrous and precious metal (Lansdown, 2010) with high value as a human commodity in jewellery and as an investment, and with wide applications in the electronics industry; approximately 24,000 tons of silver was mined and produced in 2012 (Mijnendonckx et al, 2013)
Ag1 resistance was initially found on the Salmonella enetrica serovar Typhimurium multi-resistance plasmid pMG101 from burns patients in 1975
Sequence analyses and site-directed mutagenesis established the importance of histidine and methionine containing motifs for Ag1-binding, and identified a nucleation core that initiates Ag1-mediated folding of SilE
Summary
Shiny, lustrous and precious metal (Lansdown, 2010) with high value as a human commodity in jewellery and as an investment, and with wide applications in the electronics industry; approximately 24,000 tons of silver was mined and produced in 2012 (Mijnendonckx et al, 2013). Silver has been highly valued for its broad-spectrum antimicrobial properties and has been one of the most important antimicrobial agents prior to the discovery and introduction of antibiotics. The rapid emergence of antibiotic resistance among many bacteria has rejuvenated the interest in silver as a viable alternative antimicrobial agent (Holt and Bard, 2005; Atiyeh et al, 2007; Mijnendonckx et al, 2013). The pMG101 sil resistance allowed growth of an Escherichia coli K-12 (E. coli) strain carrying pMG101, in standard LuriaBertani (LB) broth containing 600 lM of Ag1, a concentration over six times of that known to be tolerated by E. coli strains K-12 strains lacking the plasmid (Gupta et al, 1999)
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