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The First Proteomic Study of Nostoc sp. PCC 7120 Exposed to Cyanotoxin BMAA under Nitrogen Starvation
Open AccessArticle

Proteomic Insights into Starvation of Nitrogen-Replete Cells of Nostoc sp. PCC 7120 under β-N-Methylamino-L-Alanine (BMAA) Treatment

1
Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 1-40, 119992 Moscow, Russia
2
Institute of Molecular Genetics, Russian Academy of Sciences, Kurchatov Square, 2, 123182 Moscow, Russia
3
Federal Research and Clinical Centre of Physical-Chemical Medicine, 119435 Moscow, Russia
*
Author to whom correspondence should be addressed.
Toxins 2020, 12(6), 372; https://doi.org/10.3390/toxins12060372
Received: 14 April 2020 / Revised: 16 May 2020 / Accepted: 1 June 2020 / Published: 4 June 2020
(This article belongs to the Special Issue Biological Role of Cyanotoxins: Experimental and In-Field Evidence)
All cyanobacteria produce a neurotoxic non-protein amino acid β-N-methylamino-L-alanine (BMAA). However, the biological function of BMAA in the regulation of cyanobacteria metabolism still remains undetermined. It is known that BMAA suppresses the formation of heterocysts in diazotrophic cyanobacteria under nitrogen starvation conditions, and BMAA induces the formation of heterocyst-like cells under nitrogen excess conditions, by causing the expression of heterocyst-specific genes that are usually “silent” under nitrogen-replete conditions, as if these bacteria receive a nitrogen deficiency intracellular molecular signal. In order to find out the molecular mechanisms underlying this unexpected BMAA effect, we studied the proteome of cyanobacterium Nostoc sp. PCC 7120 grown under BMAA treatment in nitrogen-replete medium. Experiments were performed in two experimental settings: (1) in control samples consisted of cells grown without the BMAA treatment and (2) the treated samples consisted of cells grown with addition of an aqueous solution of BMAA (20 µM). In total, 1567 different proteins of Nostoc sp. PCC 7120 were identified by LC-MS/MS spectrometry. Among them, 80 proteins belonging to different functional categories were chosen for further functional analysis and interpretation of obtained proteomic data. Here, we provide the evidence that a pleiotropic regulatory effect of BMAA on the proteome of cyanobacterium was largely different under conditions of nitrogen-excess compared to its effect under nitrogen starvation conditions (that was studied in our previous work). The most significant difference in proteome expression between the BMAA-treated and untreated samples under different growth conditions was detected in key regulatory protein PII (GlnB). BMAA downregulates protein PII in nitrogen-starved cells and upregulates this protein in nitrogen-replete conditions. PII protein is a key signal transduction protein and the change in its regulation leads to the change of many other regulatory proteins, including different transcriptional factors, enzymes and transporters. Complex changes in key metabolic and regulatory proteins (RbcL, RbcS, Rca, CmpA, GltS, NodM, thioredoxin 1, RpbD, ClpP, MinD, RecA, etc.), detected in this experimental study, could be a reason for the appearance of the “starvation” state in nitrogen-replete conditions in the presence of BMAA. In addition, 15 proteins identified in this study are encoded by genes, which are under the control of NtcA—a global transcriptional regulator—one of the main protein partners and transcriptional regulators of PII protein. Thereby, this proteomic study gives a possible explanation of cyanobacterium starvation under nitrogen-replete conditions and BMAA treatment. It allows to take a closer look at the regulation of cyanobacteria metabolism affected by this cyanotoxin. View Full-Text
Keywords: Anabaena; nitrogen metabolism; GlnB (PII) protein; NtcA; 2-oxoglutarate; amino acids metabolism; carbon fixation; oxidative stress; RecA; thioredoxin I Anabaena; nitrogen metabolism; GlnB (PII) protein; NtcA; 2-oxoglutarate; amino acids metabolism; carbon fixation; oxidative stress; RecA; thioredoxin I
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MDPI and ACS Style

Koksharova, O.A.; Butenko, I.O.; Pobeguts, O.V.; Safronova, N.A.; Govorun, V.M. Proteomic Insights into Starvation of Nitrogen-Replete Cells of Nostoc sp. PCC 7120 under β-N-Methylamino-L-Alanine (BMAA) Treatment. Toxins 2020, 12, 372.

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