The mirB ferrisiderophore transporter of Aspergillus fumigatus: Structural requirements for activity

Siderophores (iron chelators) have been identified as virulence factors in the opportunistic fungal pathogen, Aspergillus fumigatus (Afu). The 14-pass transmembrane protein MirB is postulated to function as a siderophore-transporter, responsible for uptake of the siderophore TAFC. The aim of my research was to identify amino acids in the extracellular loops of Afu MirB that are crucial for uptake of Fe-TAFC. Site-directed mutagenesis was used to create MirB mutants and expression of the WT and mutant proteins in Saccharomyces cerevisiae strain PHY14 was confirmed by western blotting. TAFC transport assays using 55Fe-labelled TAFC and growth assays with Fe-TAFC as the sole iron source identified alanine 125, tyrosine 577, loop 3 and the second half of loop 7 as crucial for function, since their substitution or deletion abrogated uptake completely. This study has revealed critical residues important for TAFC uptake which could represent potential targets for the development of novel antifungals.