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Open AccessArticle

Novel Microcystins from Planktothrix prolifica NIVA-CYA 544 Identified by LC-MS/MS, Functional Group Derivatization and 15N-labeling

1
Toxinology Research Group, Norwegian Veterinary Institute, Ullevålsveien 68, N-0454 Oslo, Norway
2
Department of Chemistry, University of Oslo, P.O. Box 1033, N-0315 Oslo, Norway
3
National Research Council, 1411 Oxford Street, Halifax, NS B3H 3Z1, Canada
4
National Research Council, 1200 Montreal Road, Ottawa, ON K1A 0R6, Canada
*
Author to whom correspondence should be addressed.
Mar. Drugs 2019, 17(11), 643; https://doi.org/10.3390/md17110643
Received: 7 October 2019 / Revised: 8 November 2019 / Accepted: 9 November 2019 / Published: 15 November 2019
Microcystins are cyclic heptapeptides from cyanobacteria that are potent inhibitors of protein phosphatases and are toxic to animals and humans. At present, more than 250 microcystin variants are known, with variants reported for all seven peptide moieties. While d-glutamic acid (d-Glu) is highly-conserved at position-6 of microcystins, there has been only one report of a cyanobacterium (Anabaena) producing microcystins containing l-Glu at the variable 2- and 4-positions. Liquid chromatography–mass spectrometry analyses of extracts from Planktothrix prolifica NIVA-CYA 544 led to the tentative identification of two new Glu-containing microcystins, [d-Asp3]MC-ER (12) and [d-Asp3]MC-EE (13). Structure determination was aided by thiol derivatization of the Mdha7-moiety and esterification of the carboxylic acid groups, while 15N-labeling of the culture and isotopic profile analysis assisted the determination of the number of nitrogen atoms present and the elemental composition of molecular and product-ions. The major microcystin analog in the extracts was [d-Asp3]MC-RR (1). A microcystin with an unprecedented high-molecular-mass (2116 Da) was also detected and tentatively identified as a sulfide-linked conjugate of [d-Asp3]MC-RR (15) by LC–HRMS/MS and sulfide oxidation, together with its sulfoxide (16) produced via autoxidation. Low levels of [d-Asp3]MC-RW (14), [d-Asp3]MC-LR (4), [d-Asp3,Mser7]MC-RR (11), [d-Asp3]MC-RY (17), [d-Asp3]MC-RF (18), [d-Asp3]MC-RR–glutathione conjugate (19), and [d-Asp3]MC-RCit (20), the first reported microcystin containing citrulline, were also identified in the extract, and an oxidized derivative of [d-Asp3]MC-RR and the cysteine conjugate of 1 were partially characterized. View Full-Text
Keywords: cyanotoxin; microcystin; hepatotoxin; mass spectrometry; Planktothrix cyanotoxin; microcystin; hepatotoxin; mass spectrometry; Planktothrix
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Mallia, V.; Uhlig, S.; Rafuse, C.; Meija, J.; Miles, C.O. Novel Microcystins from Planktothrix prolifica NIVA-CYA 544 Identified by LC-MS/MS, Functional Group Derivatization and 15N-labeling. Mar. Drugs 2019, 17, 643.

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