Identification and substrate specificity of a ferrichrome-type siderophoretransporter (Arn1p) in Saccharomyces cerevisiae

Genes encoding transporters for heterologous siderophores have been identif ied in Saccharomyces cerevisiae, of which SIT1; TAF1, and ENB1 encode the t ransporters for ferrioxamines, ferric triacetylfursarinine C and ferric ent erobactin, respectively. In the present communication we have shown that a further gene encoding a member of the major facilitator superfamily, ARN1 ( YHL040c), is involved in the transport of a specific class of ferrichromes, possessing anhydromevalonyl residues linked to N-delta-ornithine (ARN). Fe rrirubin and ferrirhodin, which both are produced by filamentous fungi, are the most common representatives of this class of ferrichromes. A strain po ssessing a disruption in the ARN1 gene was unable to transport ferrirubin, ferrirhodin and also ferrichrome A, indicating that the encoded transporter recognizes anhydromevalonyl and the structurally-related methylglutaconyl side-chains surrounding the iron center. Ferrichromes possessing short-chai n ornithine-N-delta-acetyl residues such as ferrichrome, ferricrocin and fe rrichrysin, were excluded by the Arn1 transporter. Substitution of the iron -surrounding N-acyl chains of ferrichromes by propionyl residues had no eff ect, whereas substitution by butyryl residues led to recognition by the Aml transporter. This would indicate that a chain length of four C-atoms is su fficient to allow binding. Using different asperchromes (B1, Di) we also fo und that a minimal number of two anhydromevalonyl residues is sufficient fo r recognition by Arn Ip. Contrary to the iron-surrounding N-acyl residues, the peptide backbone of ferrichromes was not an important determinant for t he Arn1 transporter. (C) 2000 Federation of European Microbiological Societ ies. Published by Elsevier Science B.V. All rights reserved.