Fig 1.
Schematic of the interaction between the TonB-ExbB-ExbD complex in the inner membrane and its interaction with the Ferric enterobactin (FeEnt) TBDT FepA in the outer membrane of E. coli.
In this study, either FepA was labeled extracellularly with Alexa-555 or TonB was labeled intracellularly with GFP. IM: inner membrane, PG: peptidoglycan layer, OM: outer membrane.
Fig 2.
Images of the distribution of TonB (a, b) and FepA (c, d) in the membranes of E. coli at high (a, c) and low (b, d) concentrations of active fluorescent markers. At low concentration, both proteins show apparent clustering in their respective membranes.
Fig 3.
a) MSD of TonB (solid circles) and of FepA (solid squares). b) Fit to confined diffusion model for TonB (data: solid circles, fit: open circles) which gives best fit parameters of a confinement radius of μm with short-time (microsecond timescale) diffusion coefficient in the range
μm2/s. c) Fit to confined diffusion model for FepA (data: solid squares, fit: open squares) which gives best fit parameters of a confinement radius of
μm with short-time (microsecond timescale) diffusion coefficient in of
μm2/s.
Fig 4.
Effect of CCCP and ligand FeEnt on MSDs of TonB and FepA.
TonB in the presence (triangles) and absence (circles) of (a) CCCP or (c) FeEnt. FepA in the presence (upside-down triangles) and absence (squares) of (b) CCCP or (d) FeEnt. Fitting suggests that the effect of CCCP and the ligand FeEnt on the mobility of TonB is a reduction in the diffusion coefficient and confinement size and a reduction in confinement size for FepA.
Fig 5.
Effect of (a) deletion of ExbB/D (triangles), (b) presence of monoclonal antibody against FepA (triangles), and (c) presence of MreB–disrupting drug A22 (triangles) on MSDs of TonB (circles). Fitting suggests that the effect of deletion of ExbB/D and disruption of MreB is to reduce the size of confinement of TonB while the effect of anti-FepA is to increase the mobility of TonB which appears as a decrease in confinement size.
Table 1.
Parameters to fit to variable confinement size model
Table 2.
Parameters to fit mixed diffusion mode model