Authentic Heterologous Expression of the Tenellin Iterative Polyketide Synthase Nonribosomal Peptide Synthetase Requires Coexpression with an Enoyl Reductase

• Published in: Chembiochem : a European journal of chemical biology 2008-03, Vol.9 (4), p.585-594
• Main Authors: Halo, Laura M., Marshall, James W., Yakasai, Ahmed A., Song, Zhongshu, Butts, Craig P., Crump, Matthew P., Heneghan, Mary, Bailey, Andrew M., Simpson, Thomas J., Lazarus, Colin. M., Cox, Russell J.
• Format: Article
• Language: English
• Subjects: Aspergillus - enzymology; Aspergillus oryzae; Beauveria; Beauveria - enzymology; Beauveria bassiana; biosynthesis; fungi; Gene Expression Regulation, Enzymologic; heterologous expression; Mixed Function Oxygenases - metabolism; Molecular Structure; natural products; Peptide Synthases - metabolism; Polyketide Synthases - metabolism; Pyridones - chemistry; Pyridones - metabolism; Ribosomes - enzymology
• ISSN: 1439-4227; 1439-7633
• DOI: 10.1002/cbic.200700390

The tenS gene encoding tenellin synthetase (TENS), a 4239‐residue polyketide synthase nonribosomal‐peptide synthetase (PKS‐NRPS) from Beauveria bassiana, was expressed in Aspergillus oryzae M‐2‐3. This led to the production of three new compounds, identified as acyl tetramic acids, and numerous minor metabolites. Consideration of the structures of these compounds indicates that the putative C‐terminal thiolester reductase (R) domain does not act as a reductase, but appears to act as a Dieckmann cyclase (DKC). Expression of tenS in the absence of a trans‐acting ER component encoded by orf3 led to errors in assembly of the polyketide component, giving clues to the mode of programming of highly reducing fungal PKS. Coexpression of tenS with orf3 from the linked gene cluster led to the production of a correctly elaborated polyketide. The NRPS adenylation domain possibly shows the first identified fungal signature sequences for tyrosine selectivity. Total synthesis fungal style: When the ∼12 kb tenellin synthetase gene (tenS) alone was expressed in Aspergillus oryzae, at least three novel tetramic acids were synthesised, illustrating the diversity of synthetic routes available to the polyketide synthase (PKS). However, when tenS was expressed with orf3, which encodes a PKS enoyl reductase component, a single compound, pretenellin A, was produced. The tenellin synthetase gene encodes a putative C‐terminal reductase domain, but this appears to catalyse a Dieckmann cyclisation (DKC) during the synthesis of pretenellin A, rather than a reduction.