[show abstract][hide abstract] ABSTRACT: UapA, the uric acid-xanthine permease from the filamentous ascomycete Aspergillus nidulans, is one of the most thoroughly characterized purine/H(+) transporters in eukaryotes. Detailed studies have addressed its regulation of expression, at both the transcriptional and post-translational levels, in response to physiological and developmental signals. An extensive kinetic profile towards a plethora of purines and mutational analyses have established models on how UapA recognizes the purine ring and revealed specific amino acid residues involved in proper folding, topogenesis, function and specificity. The present work describes for the first time the purification of the UapA transporter of A. nidulans through overexpression via the strong, ethanol-inducible, glucose-repressible, alcA promoter. Purification, almost to homogeneity, was achieved by Ni(2+) affinity chromatography using a functional His-tagged UapA protein version. It is subsequently shown, by Circular Dichroism (CD) spectroscopy, that the purified protein is structured with a high alpha-helical content, as expected from the in silico predictions. The result of this work opens the way for further, analytical and biochemical studies on UapA at the protein level.
Protein Expression and Purification 10/2008; 63(1):33-9. · 1.43 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this article we study the cellular expression of UapA and AzgA, the two major purine transporters of Aspergillus nidulans, by constructing strains expressing, from their native promoters, fully functional fluorescent (UapA-sGFP, AzgA-sGFP) or immunological (UapA-His) chimeric transporters. Epifluorescence microscopy and immunodetection showed that under different physiological conditions and during Aspergillus development: (i) UapA and AzgA expression in the plasma membrane becomes evident early during germination and remains at a significant basal level in mycelium, (ii) Neither of the two transporters is expressed in the stalk, the vesicle, the phialides and the conidiospores, but surprisingly, UapA is specifically and strongly expressed in the periphery of metulae, (iii) Both transporters are expressed in ascogenous hyphae and in hülle cells but not in cleistothecia or ascospores, (iv) Purine induction leads to approximately 4-fold increase in UapA and AzgA protein content in mycelium, compatible with an analogous increase at the transcriptional level, (v) Ammonium leads to removal of UapA, but not of AzgA, from the plasma membrane by sorting of the protein to the vacuole.
Fungal Genetics and Biology 08/2007; 44(7):627-40. · 3.26 Impact Factor