Exploring the molecular mechanisms of Ag(I) transporters involved in bacterial Ag(I) resistance

Silver (Ag(I)) displays multiple antimicrobial properties that have led to its widespread use in the medical field. However, extensive use of Ag(I) has led to the emergence of bacterial resistance to Ag(I). Resistance to Ag(I) was inferred through the presence of plasmid pMG101 that contains a gene cluster, sil, which allowed bacteria to survive six times the normal lethal dose of Ag(I). The proteins of the sil system were given putative functions based on their sequence homology to the more extensively studied cue and cus systems, involved in copper homeostasis. To date only SilE has been characterised. This work herein describes the functional and structural characterisation of three more of the proteins of the sil system; SilP, SilF and SilC. Functional characterisation involved the use of a variety of biophysical and biochemical assays, with the former giving information on the oligomeric state of the proteins and the effects of metal binding. The biochemical assays showed that the proteins are able to bind or interact with Ag(I) and Cu(I), with preferential binding to Ag(I). SilP, a P-type ATPase, activity assays suggest a modified catalytic cycle that challenges the current cycles attributed to other P-type ATPases. Structural studies utilised x-Ray crystallography to produce atomic models for both SilF and SilC. While SilP was investigated using Cryo-Electron Microscopy, which showed the protein is dimeric on grids and a viable target for future work. The functional and structural analysis within this thesis expands the limited understanding of the sil system and has significance for the future development of inhibitors of the proteins involved in bacterial silver resistance