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A tyrosine O-prenyltransferase catalyses the first pathway-specific step in the biosynthesis of sirodesmin PL

University of Marburg

A putative prenyltransferase gene sirD was identified in the biosynthetic gene cluster of the phytotoxin sirodesmin PL in Leptosphaeria maculans. The gene product comprises 449 amino acids with a molecular mass of 51 kDa. In this study, the coding region of sirD was amplified by PCR from cDNA, cloned into pQE70 and overexpressed in Escherichia coli. The overproduced protein was purified to apparent homogeneity and characterised biochemically. The dimeric recombinant SirD was found to catalyse the O-prenylation of L-tyrosine in the presence of dimethylallyl diphosphate, which was proven unequivocally by isolation and structural elucidation of the enzymatic product. Therefore, SirD catalyses the first pathway-specific step in the biosynthesis of sirodesmin PL. KM values for L-tyrosine and dimethylallyl diphosphate were determined as 0.13 and 0.17 mM, respectively. Interestingly, SirD shares significant sequence similarity with indole prenyltransferases, which catalyse prenyl transfer reactions onto different positions of indole rings. In contrast to indole prenyltransferases, which accepted indole derivatives, but not tyrosine or structures derived thereof as substrates, SirD prenylated also L-tryptophan resulting in formation of 7-dimethylallyltryptophan. A KM value of 0.23 mM was determined for L-tryptophan. Turnover numbers were calculated for L-tyrosine and L-tryptophan at 1.0 and 0.06 S-1, respectively.

¹ E-mail: lishu{at}staff.uni-marburg.de