Figure 1

Figure 1

(A) Main features of microcin E492 peptide and its production by bacterial cells, through the expression of the mce genes from the MccE492 gene cluster. The mceA gene encodes the microcin precursor that includes a leader peptide that is removed during the export by ABC exporters encoded by mceHG. During maturation, salmochelin (a glycosylated enterochelin derivative synthetized by MceC) is attached to MccE492 C-terminus by MceIJ. Mature MccE492 is recognized and internalized by catechol siderophore receptors of the target bacterial cell, and once in the periplasm it inserts into the cytoplasmic membrane in a TonB-dependent process forming pores that lead to a toxic effect through the disruption of the membrane potential of the cell. Additionally, under certain conditions, MccE492 aggregates into amyloid fibers and rod-shaped nanostructures, leading to the loss of its antibacterial activity. MccE492 also has toxic activity in vitro against some tumor cell lines, although its in vivo antitumoral effect has not been validated in animal models. For simplicity, several genes from the MccE492 gene cluster are not included, among them the immunity gene mceB that is encoded in an operon with the structural gene mceA. (B) Antibacterial activity assay of a representative MccE492 preparation (either the ACN fraction or after lyophilization) assessed through the detection of growth inhibition halos over sensitive bacterial lawns. The red dots correspond to the zone of the lawn where the drops of MccE492 or the mock preparation were placed. (C) SDS-PAGE and immunoblot of a representative MccE492 preparation (either the ACN fraction or after lyophilization), revealed with a monoclonal anti-McccE492 antibody. The last lane of the immunoblot image (showing mock purification) was spliced together with the first 3 lanes, to avoid showing blank (non-loaded) lanes.