title: Dynamic proteomic profiling of a unicellular cyanobacterium Cyanothece ATCC51142 across light-dark diurnal cycles.
abstract: BACKGROUND
  Unicellular cyanobacteria of the genus Cyanothece are recognized for their ability to execute nitrogen (N2)-fixation in the dark and photosynthesis in the light. An understanding of these mechanistic processes in an integrated systems context should provide insights into how Cyanothece might be optimized for specialized environments and/or industrial purposes. Systems-wide dynamic proteomic profiling with mass spectrometry (MS) analysis should reveal fundamental insights into the control and regulation of these functions.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors: Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors: Uma K
authors: UK
authors: Aryal
authors: Jana
authors: J
authors: Stöckel
authors: Ravi K
authors: RK
authors: Krovvidi
authors: Marina A
authors: MA
authors: Gritsenko
authors: Matthew E
authors: ME
authors: Monroe
authors: Ronald J
authors: RJ
authors: Moore
authors: David W
authors: DW
authors: Koppenaal
authors: Richard D
authors: RD
authors: Smith
authors: Himadri B
authors: HB
authors: Pakrasi
authors: Jon M
authors: JM
authors: Jacobs
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002940:Circadian Rhythm; D046889:Cyanothece / Q000235:genetics / Q000378:metabolism*; D003624:Darkness; D008027:Light; D008954:Models, Biological; D009586:Nitrogen Fixation; D010788:Photosynthesis; D060066:Protein Interaction Maps; D020543:Proteome; D040901:Proteomics; D013312:Stress, Physiological; D049490:Systems Biology; D059467:Transcriptome
chemical_list: D001426:Bacterial Proteins; D020543:Proteome