title: Natural occurrence of microcystin synthetase deletion mutants capable of producing microcystins in strains of the genus Anabaena (Cyanobacteria).
abstract: 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.
authors: Department of Applied Chemistry and Microbiology, PO Box 56, Viikki Biocenter, Viikinkaari 9, FIN-00014, University of Helsinki, Finland.
authors: David P
authors: DP
authors: Fewer
authors: Institute of Molecular Biosciences, PO Box 1041, Blindern, University of Oslo, Norway.
authors: Ave
authors: A
authors: Tooming-Klunderud
authors: Department of Applied Chemistry and Microbiology, PO Box 56, Viikki Biocenter, Viikinkaari 9, FIN-00014, University of Helsinki, Finland.
authors: Jouni
authors: J
authors: Jokela
authors: Department of Applied Chemistry and Microbiology, PO Box 56, Viikki Biocenter, Viikinkaari 9, FIN-00014, University of Helsinki, Finland.
authors: Matti
authors: M
authors: Wahlsten
authors: Department of Applied Chemistry and Microbiology, PO Box 56, Viikki Biocenter, Viikinkaari 9, FIN-00014, University of Helsinki, Finland.
authors: Leo
authors: L
authors: Rouhiainen
authors: Institute of Molecular Biosciences, PO Box 1041, Blindern, University of Oslo, Norway.
authors: Tom
authors: T
authors: Kristensen
authors: NIVA - Norwegian Institute for Water Research, 0441 Oslo, Norway.
authors: Thomas
authors: T
authors: Rohrlack
authors: Centre for Ecological and Evolutionary Synthesis, Department of Biology, University of Oslo, Norway.
authors: Kjetill S
authors: KS
authors: Jakobsen
authors: Department of Applied Chemistry and Microbiology, PO Box 56, Viikki Biocenter, Viikinkaari 9, FIN-00014, University of Helsinki, Finland.
authors: Kaarina
authors: K
authors: Sivonen
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives / Q000378:metabolism; D017033:Anabaena / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D052998:Microcystins / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010453:Peptide Synthases / Q000737:chemistry / Q000235:genetics*; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D017434:Protein Structure, Tertiary; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion; D017385:Sequence Homology; D012694:Serine / Q000378:metabolism; D014871:Water Microbiology
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D052998:Microcystins; D012694:Serine; C078588:microcystin; C037064:N-methyldehydroalanine; C015102:dehydroalanine; D010453:Peptide Synthases; C432283:microcystin synthetase A; D000409:Alanine