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Dynamic proteomic profiling of a unicellular cyanobacterium Cyanothece ATCC51142 across light-dark diurnal cycles

DOI: 10.1186/1752-0509-5-194

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To expand upon the current knowledge of protein expression patterns in Cyanothece ATCC51142, we performed quantitative proteomic analysis using partial ("unsaturated") metabolic labeling and high mass accuracy LC-MS analysis. This dynamic proteomic profiling identified 721 actively synthesized proteins with significant temporal changes in expression throughout the light-dark cycles, of which 425 proteins matched with previously characterized cycling transcripts. The remaining 296 proteins contained a cluster of proteins uniquely involved in DNA replication and repair, protein degradation, tRNA synthesis and modification, transport and binding, and regulatory functions. Functional classification of labeled proteins suggested that proteins involved in respiration and glycogen metabolism showed increased expression in the dark cycle together with nitrogenase, suggesting that N2-fixation is mediated by higher respiration and glycogen metabolism. Results indicated that Cyanothece ATCC51142 might utilize alternative pathways for carbon (C) and nitrogen (N) acquisition, particularly, aspartic acid and glutamate as substrates of C and N, respectively. Utilization of phosphoketolase (PHK) pathway for the conversion of xylulose-5P to pyruvate and acetyl-P likely constitutes an alternative strategy to compensate higher ATP and NADPH demand.This study provides a deeper systems level insight into how Cyanothece ATCC51142 modulates cellular functions to accommodate photosynthesis and N2-fixation within the single cell.Oxygenic photosynthetic cyanobacteria are widely recognized for their important role in the global carbon cycle [1], and have generated significant interest as a potential solution for carbon-neutral energy production and carbon (C) sequestration [2]. Some unicellular cyanobacteria such as Cyanothece and Crocosphaera are also capable of biological N2-fixation (diazotrophic) [3], and play a significant role in marine nitrogen (N) cycle [4]. One of the most important


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