title: Proteomics analysis of high lipid-producing strain Mucor circinelloides WJ11: an explanation for the mechanism of lipid accumulation at the proteomic level.
abstract: BACKGROUND
  The oleaginous fungus, Mucor circinelloides, is attracting considerable interest as it produces oil rich in γ-linolenic acid. Nitrogen (N) deficiency is a common strategy to trigger the lipid accumulation in oleaginous microorganisms. Although a simple pathway from N depletion in the medium to lipid accumulation has been elucidated at the enzymatic level, global changes at protein levels upon N depletion have not been investigated. In this study, we have systematically analyzed the changes at the levels of protein expression in M. circinelloides WJ11, a high lipid-producing strain (36 %, lipid/cell dry weight), during lipid accumulation.
  
  
  RESULTS
  Proteomic analysis demonstrated that N depletion increased the expression of glutamine synthetase, involved in ammonia assimilation, for the supply of cellular nitrogen but decreased the metabolism of amino acids. Upon N deficiency, many proteins (e.g., fructose-bisphosphate aldolase, glyceraldehyde-3-phosphate dehydrogenase, enolase, pyruvate kinase) involved in glycolytic pathway were up-regulated while proteins involved in the tricarboxylic acid cycle (e.g., isocitrate dehydrogenase, succinyl-CoA ligase, succinate dehydrogenase, fumarate hydratase) were down-regulated, indicating this activity was retarded thereby leading to a greater flux of carbon into fatty acid biosynthesis. Moreover, glucose-6-phosphate dehydrogenase, transaldolase and transketolase, which participate in the pentose phosphate pathway, were up-regulated, leading to the increased production of NADPH, the reducing power for fatty acid biosynthesis. Furthermore, protein and nucleic acid metabolism were down-regulated and some proteins involved in energy metabolism, signal transduction, molecular chaperone and redox homeostasis were up-regulated upon N depletion, which may be the cellular response to the stress produced by the onset of N deficiency.
  
  
  CONCLUSIONS
  N limitation increased those expressions of the proteins involved in ammonia assimilation but decreased that involved in the biosynthesis of amino acids. Upon N deprivation, the glycolytic pathway was up-regulated, while the activity of the tricarboxylic acid cycle was retarded, thus, leading more carbon flux to fatty acid biosynthesis. Moreover, the pentose phosphate pathway was up-regulated, then this would increase the production of NADPH. Together, coordinated regulation of central carbon metabolism upon N limitation, provides more carbon flux to acetyl-CoA and NADPH for fatty acid biosynthesis.
authors: State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People's Republic of China. tangxin_801@163.com.
authors: Xin
authors: X
authors: Tang
authors: State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People's Republic of China. zxy19880920@163.com.
authors: Xinyi
authors: X
authors: Zan
authors: State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People's Republic of China. linabobo0706@163.com.
authors: Lina
authors: L
authors: Zhao
authors: State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People's Republic of China. haiqinchen@jiangnan.edu.cn.|Synergistic Innovation Center for Food Safety and Nutrition, Wuxi, People's Republic of China. haiqinchen@jiangnan.edu.cn.
authors: Haiqin
authors: H
authors: Chen
authors: State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People's Republic of China. yqchen@wakehealth.edu.|Synergistic Innovation Center for Food Safety and Nutrition, Wuxi, People's Republic of China. yqchen@wakehealth.edu.
authors: Yong Q
authors: YQ
authors: Chen
authors: State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People's Republic of China. weichen@jiangnan.edu.cn.|Synergistic Innovation Center for Food Safety and Nutrition, Wuxi, People's Republic of China. weichen@jiangnan.edu.cn.
authors: Wei
authors: W
authors: Chen
authors: State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, People's Republic of China. ysong@jiangnan.edu.cn.|Colin Ratledge Center for Microbial Lipids, School of Agriculture Engineering and Food Science, Shandong University of Technology, Zibo, People's Republic of China. ysong@jiangnan.edu.cn.
authors: Yuanda
authors: Y
authors: Song
authors: Department of Biological Sciences, University of Hull, Hull, UK. C.Ratledge@hull.ac.uk.
authors: Colin
authors: C
authors: Ratledge
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D002244:Carbon / Q000378:metabolism; D005800:Genes, Fungal; D050356:Lipid Metabolism / Q000187:drug effects; D008055:Lipids / Q000096:biosynthesis*; D053858:Metabolic Networks and Pathways / Q000187:drug effects / Q000235:genetics; D009089:Mucor / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism / Q000494:pharmacology; D020543:Proteome / Q000378:metabolism*; D040901:Proteomics / Q000379:methods*; D060888:Real-Time Polymerase Chain Reaction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D000596:Amino Acids; D008055:Lipids; D020543:Proteome; D002244:Carbon; D009584:Nitrogen