Fig 1. Stimulation dependence of interactions between PTS components.

(A) Schematic representation of a part of the PTS network that shows branches for uptake of glucose (EII^Glc and EII^Mal), mannose (EII^Man), and N-acetylglucosamine (GlcNAc) (EII^Nag). Phosphotransfer reactions between components are shown with solid lines and observed stimulation-dependent protein interactions are shown with dashed lines. Note that EIIA^Glc is shared between EII^Glc and EII^Mal, and EII^Man has an additional component EIID^Man. (B) Example of a FRET measurement for a pair of glucose-specific PTS components. Cells expressing EIIA^Glc-CFP and EIICB^Mal-YFP were stimulated by the stepwise addition of PTS sugars and the response was followed as a change in the ratio of YFP to CFP fluorescence. Measurements were acquired every second for a population of several hundred cells, as described in Materials and Methods. (C) Example of a FRET measurement for a EIIAB^Man-YFP and EIIC^Man-CFP pair upon stimulation by the stepwise addition of 100 μM of the indicated PTS sugars. (D) The amplitude of FRET response for indicated pairs to saturating levels (100 μM) of PTS sugars, normalized to the glucose response. Error bars indicate standard errors of the mean of three independent replicates. The underlying data for Fig 1D can be found in S1 Data. (E) Signaling equivalency of different PTS sugars. Cells expressing EI-CFP and EIICBA^Nag -YFP were stimulated with the indicated subsaturating concentrations of mannitol, GlcNAc or glucose. The response to a saturating glucose stimulus is shown for a reference.