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Mol Microbiol. 2009 Sep;73(5):924-37. doi: 10.1111/j.1365-2958.2009.06816.x. Epub 2009 Aug 19.

The non-ribosomal assembly and frequent occurrence of the protease inhibitors spumigins in the bloom-forming cyanobacterium Nodularia spumigena.

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1
Department of Applied Chemistry and Microbiology, University of Helsinki, Viikki Biocenter, Viikinkaari, Finland.

Abstract

Nodularia spumigena is a filamentous nitrogen-fixing cyanobacterium that forms toxic blooms in brackish water bodies worldwide. Spumigins are serine protease inhibitors reported from a single strain of N. spumigena isolated from the Baltic Sea. These linear tetrapeptides contain non-proteinogenic amino acids including a C-terminal alcohol derivative of arginine. However, very little is known about these compounds despite the ecological importance of N. spumigena. We show that spumigins are assembled by two non-ribosomal peptide synthetases encoded in a 21 kb biosynthetic gene cluster. The compact non-ribosomal peptide synthetase features a reductive loading and release mechanism. Our analyses demonstrate that the bulk of spumigins produced by N. spumigena are released as peptide aldehydes in contrast to earlier findings. The main spumigin E variant contains an argininal residue and is a potent trypsin inhibitor. Spumigins were present in all of the N. spumigena strains isolated from the Baltic Sea and comprised up to 1% of the dry weight of the cyanobacterium. Our results demonstrate that bloom-forming N. spumigena strains produce a cocktail of enzyme inhibitors, which may explain in part the ecological success of this cyanobacterium in brackish water bodies worldwide.

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