FIGURE 4.

Substrate specificity of MarP determined using multiplex substrate profiling by mass spectrometry. A, a list of all cleavage sites observed over the course of the assay is shown. Only P4 to P4′ residues are shown, and the time at which the cleavage was first observed is indicated at the top of each list. When cleavage occurs near the N or C termini, then some subsites are not occupied by an amino acid and are represented as a blank space. B, an iceLogo represents amino acids that are most frequently (above the axis) and least frequently (below the axis) observed in each of the 25 cleavage sites. Residues that are highlighted in black text are significantly (p = 0.05) enriched in the MarP subsites relative to the frequency that these same amino acids are found in the peptide library (5.2 ± 0.5%).