β-N-Methylamino-L-Alanine (BMAA) Causes Severe Stress in Nostoc sp. PCC 7120 Cells under Diazotrophic Conditions: A Proteomic Study

Abstract

Non-proteinogenic neurotoxic amino acid β-N-methylamino-L-alanine (BMAA) is synthesized by cyanobacteria, diatoms, and dinoflagellates, and is known to be a causative agent of human neurodegenerative diseases. Different phytoplankton organisms’ ability to synthesize BMAA could indicate the importance of this molecule in the interactions between microalgae in nature. We were interested in the following: what kinds of mechanisms underline BMAA’s action on cyanobacterial cells in different nitrogen supply conditions. Herein, we present a proteomic analysis of filamentous cyanobacteria Nostoc sp. PCC 7120 cells that underwent BMAA treatment in diazotrophic conditions. In diazotrophic growth conditions, to survive, cyanobacteria can use only biological nitrogen fixation to obtain nitrogen for life. Note that nitrogen fixation is an energy-consuming process. In total, 1567 different proteins of Nostoc sp. PCC 7120 were identified by using LC-MS/MS spectrometry. Among them, 123 proteins belonging to different functional categories were selected—due to their notable expression differences—for further functional analysis and discussion. The presented proteomic data evidences that BMAA treatment leads to very strong (up to 80%) downregulation of α (NifD) and β (NifK) subunits of molybdenum-iron protein, which is known to be a part of nitrogenase. This enzyme is responsible for catalyzing nitrogen fixation. The genes nifD and nifK are under transcriptional control of a global nitrogen regulator NtcA. In this study, we have found that BMAA impacts in a total of 22 proteins that are under the control of NtcA. Moreover, BMAA downregulates 18 proteins that belong to photosystems I or II and light-harvesting complexes; BMAA treatment under diazotrophic conditions also downregulates five subunits of ATP synthase and enzyme NAD(P)H-quinone oxidoreductase. Therefore, we can conclude that the disbalance in energy and metabolite amounts leads to severe intracellular stress that induces the upregulation of stress-activated proteins, such as starvation-inducible DNA-binding protein, four SOS-response enzymes, and DNA repair enzymes, nine stress-response enzymes, and four proteases. The presented data provide new leads into the ecological impact of BMAA on microalgal communities that can be used in future investigations.

Non-Proteinogenic Amino Acid β-N-Methylamino-L-Alanine (BMAA): Bioactivity and Ecological Significance

“…BMAA showed no mutagenic, cytotoxic, or genotoxic effects on several strains of the heterotrophic bacterium Salmonella typhimurium [158]. At the same time, the photoautotrophic growth of cyanobacteria was inhibited by exogenous BMAA in micromolar amounts [104][105][106][107][108][109]159]. Moreover, the results of many published studies [57] demonstrate that BMAA was found mainly in protein-associated fractions of cyanobacterial cells.…”

“…The effect of BMAA has been studied mainly on various animal models and human cell cultures due to its harmful consequences for health [78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97]. There are several studies on the effects of BMAA on plant cells [98][99][100][101][102], diatoms [103], and cyanobacteria [27,37,[104][105][106][107][108][109][110][111]. The biological actions of BMAA on eukaryotic and prokaryotic cells can be explained by various mechanisms [13,78] (Figure 3).…”

“…BMAA binds transition metal ions, such as Zn 2+ , Cu 2+ , and Ni 2+ [126][127][128][129][130]. BMAA alters the regulation of nitrogen metabolism and photosynthesis in cyanobacteria [36,37,[104][105][106][107][108][109]. Exposure to BMAA impairs the morphogenesis process and causes oxidative stress, DNA repair, and apoptosis [107][108][109][131][132][133][134].…”

“…BMAA alters the regulation of nitrogen metabolism and photosynthesis in cyanobacteria [36,37,[104][105][106][107][108][109]. Exposure to BMAA impairs the morphogenesis process and causes oxidative stress, DNA repair, and apoptosis [107][108][109][131][132][133][134]. The persistent nature of the effects caused by BMAA may be associated with epigenetic changes, since exposure to BMAA reduces global DNA methylation in cells [134].…”

FurC (PerR) contributes to the regulation of peptidoglycan remodeling and intercellular molecular transfer in the cyanobacterium Anabaena sp. strain PCC 7120

“…As cyanobacteria are exposed to dynamic environmental conditions, they have developed sophisticated defense and detoxification systems to ameliorate the consequences of stress-induced reactive oxygen species (ROS). While the dynamics of cyanobacterial intracellular processes related to stress responses has been studied intensively ( 1 – 12 ), there are significant gaps in our understanding of the stresses managed in the extracellular space. In addition to a variety of exometabolites, cyanobacterial extracellular milieu is rich in proteins, whether they are actively secreted or not ( 13 – 18 ).…”