Abstract:

FurE, a member of the NCS1 family, is an Aspergillus nidulans transporter specific for uracil, allantoin and uric acid. Recently, we showed that C- or N-terminally truncated FurE versions are blocked for endocytosis and, surprisingly, show modified substrate specificities. Bifluorescence complementation assays and genetic analyses supported the idea that C- and N-termini interact dynamically and through this interaction regulate selective substrate translocation. Here we functionally dissect and define distinct motifs crucial for endocytosis, transport activity, substrate specificity and folding, in both cytosolic termini of FurE. Subsequently, we obtain novel genetic and in silico evidence indicating that the molecular dynamics of specific N- and C-terminal regions exert long range effects on the gating mechanism responsible for substrate selection, via pH-dependent interactions with other internal cytosolic loops and membrane lipids. Our work shows that expanded cytoplasmic termini, acquired through evolution mostly in eukaryotic transporters, provide novel specific functional roles.