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1 Department of Applied Chemistry and Microbiology, PO Box 56, Viikki Biocenter, Viikinkaari 9, FIN-00014, University of Helsinki, Finland
2 Institute of Molecular Biosciences, PO Box 1041, Blindern, University of Oslo, Norway
3 NIVA – Norwegian Institute for Water Research, 0441 Oslo, Norway
4 Centre for Ecological and Evolutionary Synthesis, Department of Biology, University of Oslo, Norway
Correspondence
Kaarina Sivonen
kaarina.sivonen{at}helsinki.fi
Microcystins form a large family of small cyclic heptapeptides harbouring extensive modifications in amino acid residue composition and functional group chemistry. These peptide hepatotoxins contain a range of non-proteinogenic amino acids and unusual peptide bonds, and are typically N-methylated. They are synthesized on large enzyme complexes consisting of non-ribosomal peptide synthetases and polyketide synthases in a variety of distantly related cyanobacterial genera. Here we report a 1236 bp in-frame deletion mutation in the mcyA gene of the microcystin biosynthetic pathway in nine strains of the genus Anabaena. The deletion removed almost the entire N-methyltransferase (NMT) domain. Strains of Anabaena carrying the in-frame deletion mutation incorporated mainly dehydroalanine (Dha) into the microcystins they produce while strains with full-length mcyA genes incorporated mainly N-methyldehydroalanine (Mdha). Interestingly, the strains of Anabaena lacking the NMT domain also incorporated elevated amounts of L-Ser, the precursor of Mdha and Dha, into the microcystin they produced relative to strains carrying functional NMT domains. We provide evidence for the in-frame deletion of the NMT domain without the co-conversion of the flanking adenylation domain. Our results demonstrate a further example of the strategies employed by cyanobacteria in the biosynthesis of microcystin variants.
A supplementary table with details of the microcystin variants produced by the 26 strains of Anabaena studied is available with the online version of this paper.
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A. Tooming-Klunderud, B. Mikalsen, T. Kristensen, and K. S. Jakobsen The mosaic structure of the mcyABC operon in Microcystis Microbiology, July 1, 2008; 154(7): 1886 - 1899. [Abstract] [Full Text] [PDF] |
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