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A 7-dimethylallyltryptophan synthase from Aspergillus fumigatus: overproduction, purification and biochemical characterization

¹ Heinrich-Heine-Universität Düsseldorf, Institut für Pharmazeutische Biologie und Biotechnologie, Universitätsstrasse 1, D-40225 Düsseldorf, Germany
² Eberhard-Karls-Universität Tübingen, Pharmazeutische Biologie, Auf der Morgenstelle 8, D-72076 Tübingen, Germany

Correspondence
Shu-Ming Li
shuming.li{at}uni-duesseldorf.de

A putative prenyltransferase gene, Afu3g12930, was identified in the genome sequence of Aspergillus fumigatus. EAL92290, encoded by Afu3g12930, consists of 472 aa, with a molecular mass of about 53 kDa. The coding sequence of Afu3g12930 was cloned in pQE60, and overexpressed in Escherichia coli. The soluble His₆-fusion protein was purified to apparent homogeneity, and characterized biochemically. The enzyme was found to catalyse the prenylation of Trp at the C-7 position of the indole moiety, in the presence of dimethylallyl diphosphate (DMAPP); therefore, it functions as a 7-dimethylallyltryptophan synthase (7-DMATS). The structure of the enzymic product was elucidated by NMR and MS analysis. K_m values were 67 µM for DMAPP, and 137 µM for L-Trp. Geranyl diphosphate was not accepted as prenyl donor, while Trp-containing dipeptides were found to be aromatic substrates of 7-DMATS. 7-DMATS did not need divalent metal ions for its enzymic reaction, although Ca²⁺ enhanced the reaction velocity slightly. The enzyme is the second dimethylallyltryptophan synthase identified in A. fumigatus. Interestingly, it shares a sequence identity of only 31 % at the amino acid level with another known dimethylallyltryptophan synthase, FgaPT2, from the same fungus; FgaPT2 prenylates L-Trp at the C-4 position of the indole ring. Afu3g12930 belongs to a putative biosynthetic gene cluster consisting of eight genes. Orthologous clusters were also identified in the genome sequences of Neosartorya fischeri and Aspergillus terreus. The putative roles of the genes in the cluster are discussed.

The GenBank/EMBL/DDBJ accession number for the nucleotide sequence reported in this paper is EF539173.

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