Fig. 4.

The pore of the FyuA β-domain is too small to transport directly folded pesticin or the thermostable hybrid across the outer membrane. The β-domain of FyuA is shown in light green and the plug domain in red, yersiniabactin (ybt) in spheres, pesticin (pst) in gold, and thermostable pst-hybrid (TS-hybrid) in dark green with the location of the engineered disulfide shown as yellow spheres (Fig. S4). For comparison, dimensions of the FyuA pore, Ybt, Pst, and TS-hybrid are shown with units in nanometers. The top row represents a periplasmic view up through the pore of the FyuA beta domain, whereas the middle row represents a membrane (side) view. The bottom row shows an overlay of FyuA with Ybt and Pst illustrating the size restrictions preventing direct transport of Pst (assuming the plug domain is fully ejected).