Post‐translational modifications of the AFET3 gene product—a component of the iron transport system in budding cells and mycelia of the yeast Arxula adeninivorans

The yeast Arxula adeninivorans is characterized by a temperature‐dependent dimorphism. A. adeninivorans grows as budding cells at temperatures up to 42°C, but forms mycelia at higher temperatures. A strong correlation exists between morphological status and iron uptake, achieved by two transport systems that differ in iron affinity. In the presence of high Fe(II) concentrations (>2 µm), budding cells accumulate iron concentrations up to seven‐fold higher than those observed in mycelia, while at low Fe(II) concentrations (<2 µm), both cell types accumulate similar amounts of iron. The copper‐dependent Fe(II) oxidase Afet3p, composed of 615 amino acids, is a component of the high‐affinity iron transport system. This protein shares a high degree of homology with other yeast iron transport proteins, namely Fet3p of Saccharomyces cerevisiae , Cafet3p of Candida albicans and Pfet3p of Pichia pastoris . Expression of the AFET3 gene is found to be strongly dependent on iron concentration but independent of the morphological stage; however, cell morphology was found to influence post‐translational modifications of the gene product. O ‐glycosylation was observed in budding cells only, whereas N ‐glycosylation occurred in both cell types. The N ‐glycosylated 103 kDa glycoprotein matures into the 108.5 kDa form, further characterized by serine phosphorylation. Both N ‐glycosylation and phosphorylation occur at low iron concentrations (≤5 µm). The mature Afet3p of 108.5 kDa is uniformly distributed within the plasma membrane in cells of both morphological stages. Copyright © 2002 John Wiley & Sons, Ltd.