Site-directed mutagenesis of loop L3 of sucrose porin ScrY leads to changes in substrate selectivity

The difference in substrate selectivity of the maltodextrin (LamB) and sucr ose (ScrY) porins is attributed mainly to differences in loop L3, which is supposed to constrict the lumen of the pores. We show that even a single mu tation (D201Y) in loop L3 leads to a narrowing of the substrate range of Sc rY to that resembling LamB. In addition, we removed the putative N-terminal coiled-coil structure of ScrY and studied the effect of this deletion on s ucrose transport.