Updated project metadata. Using a shotgun proteomics approach, the expressed proteome of total membrane fractions of Escherichia coli ATCC25922 cells was analyzed under i) normal growth, and ii) treatment with the novel peptidomimetic JB-95 (a structurally arrested cyclic peptide). By selectively disrupturing the outer membrane (OM), this peptidomimetic displayed a novel mechanism of action and opens new avenues for developing antibiotics that specifically target the OM of Gram-negative bacteria.