title: Quantitative iTRAQ LC-MS/MS proteomics reveals the cellular response to heterologous protein overexpression and the regulation of HAC1 in Pichia pastoris.
abstract: The methylotrophic yeast Pichia pastoris is an attractive platform for a plethora of recombinant proteins. There is growing evidence that host cells producing recombinant proteins are exposed to a variety of cellular stresses resulting in the induction of the unfolded protein response (UPR) pathway. At present, there is only limited information about the cellular reactions of the host cells at the level of the proteome, especially with regard to recombinant protein secretion. Here we monitored xylanase A secretion from Bacillus halodurans C-125 (xynA) in P. pastoris, using strains containing different copy numbers of the gene encoding xylanase A and co-overexpressing the gene encoding the UPR-regulating transcription factor HAC1 by applying a quantitative proteomics approach (iTRAQ-LC-MS/MS). Many important cellular processes, including carbon metabolism, stress response and protein folding are affected in the investigated conditions. Notably, the analysis revealed that strong over-expression of xynA can efficiently improve protein production but simultaneously cause an unfolded protein burden with a subsequent induction of the UPR. This limits the further improvement of protein production levels. Remarkably, constitutive expression of the gene encoding HAC1 lessens the unfolded protein burden by attenuating protein synthesis and increasing ER protein folding efficiency which is beneficial for protein secretion.
  
  
  CONCLUSIONS
  Pichia pastoris expression systems have been successfully used for over 20years in basic research and in the biotechnology industry for the production and secretion of a wide range of recombinant proteins. In particular, secretion of recombinant proteins is still one of the main reasons for using P. pastoris. It has become obvious that many protein products can lead to severe stress on the host cell when being over-expressed, thus limiting the potential yield. Detailed understanding of the physiological responses to such stresses gives rise to engineering of host cells that can better cope with the stress factors. Therefore, the regulatory mechanism of heterologous protein secretion by quantitative mass-spectrometry (MS) proteomics is a growing field and an important endeavor in improving protein annotation. Many important cellular processes, including carbon and amino acid metabolism, stress response and protein folding are affected in the over-expression strains. This data represent a first step towards a systems wide approach to assess the response with recombinant protein induced stress in P. pastoris.
authors.affiliation: Guangdong Key Laboratory of Fermentation and Enzyme Engineering, School of Bioscience and Bioengineering, South China University of Technology, Guangzhou 510006, PR China.
authors.forename: Xiao-qiong
authors.initials: XQ
authors.lastname: Lin
authors.forename: Shu-li
authors.initials: SL
authors.lastname: Liang
authors.forename: Shuang-yan
authors.initials: SY
authors.lastname: Han
authors.forename: Sui-ping
authors.initials: SP
authors.lastname: Zheng
authors.forename: Yan-rui
authors.initials: YR
authors.lastname: Ye
authors.forename: Ying
authors.initials: Y
authors.lastname: Lin
mesh_terms: D001407:Bacillus / Q000378:metabolism; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism*; D002952:Citric Acid Cycle; D043364:Endo-1,4-beta Xylanases / Q000235:genetics / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D006019:Glycolysis; D018832:Molecular Chaperones / Q000378:metabolism; D010427:Pentose Phosphate Pathway; D010843:Pichia / Q000235:genetics / Q000378:metabolism*; D017510:Protein Folding; D020543:Proteome; D040901:Proteomics; D012097:Repressor Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D053719:Tandem Mass Spectrometry; D014157:Transcription Factors / Q000378:metabolism*; D056811:Unfolded Protein Response
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D005656:Fungal Proteins; C091341:HAC1 protein, S cerevisiae; D018832:Molecular Chaperones; D020543:Proteome; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D043364:Endo-1,4-beta Xylanases
keywords: HAC1; Pichia pastoris; Unfolded protein response (UPR); Xylanase; iTRAQ