A-B. PBP4 has different interaction sites for PBP1A/LpoA and NlpI as shown by a single concentration MST assay. Plots show the FNorm or fluorescence values of fluorescently labelled PBP1A or LpoA with or without PBP4, NlpI or PBP4-NlpI. Values are mean ± standard deviation of three independent experiments. 