Screens for mutants defective in UapA trafficking highlight the importance of ER-exit as a primary control point in transporter biogenesis.

Most transmembrane membrane proteins are thought to traffic to the plasma membrane (PM) via the conventional secretory pathway through sorting from the Golgi. However, our recent work has shown that in the filamentous fungus Aspergillus nidulans several nutrient transporters and other major membrane proteins traffic to the PM via Golgi-bypass and independently of known post-Golgi secretory mechanisms. Here in an effort to dissect the molecular mechanism underlying membrane cargo trafficking via Golgi-bypass we design and use unbiased genetic screens, based on the UapA uric acid-xanthine transporter, which allowed the isolation of mutants defective in UapA translocation to the plasma membrane.

Distinct trafficking routes of polarized and non-polarized membrane cargoes in .

Membrane proteins are sorted to the plasma membrane via Golgi-dependent trafficking. However, our recent studies challenged the essentiality of Golgi in the biogenesis of specific transporters. Here, we investigate the trafficking mechanisms of membrane proteins by following the localization of the polarized R-SNARE SynA versus the non-polarized transporter UapA, synchronously co-expressed in wild-type or isogenic genetic backgrounds repressible for conventional cargo secretion.

High-resolution structures of the UapA purine transporter reveal unprecedented aspects of the elevator-type transport mechanism.

UapA is an extensively studied elevator-type purine transporter from the model fungus . Determination of a 3.6Å inward-facing crystal structure lacking the cytoplasmic N-and C-tails, molecular dynamics (MD), and functional studies have led to speculative models of its transport mechanism and determination of substrate specificity.

The last two transmembrane helices in the APC-type FurE transporter act as an intramolecular chaperone essential for concentrative ER-exit.

FurE is a H symporter specific for the cellular uptake of uric acid, allantoin, uracil, and toxic nucleobase analogues in the fungus nidulans. Being member of the NCS1 protein family, FurE is structurally related to the APC-superfamily of transporters. APC-type transporters are characterised by a 5+5 inverted repeat fold made of ten transmembrane segments (TMS1-10) and function through the rocking-bundle mechanism.