Analysis of membrane and hydrophilic proteins simultaneously derived from the mouse brain using cloud-point extraction

Anal Bioanal Chem. 2011 Jul;400(9):2827-36. doi: 10.1007/s00216-011-5037-9. Epub 2011 May 7.

Abstract

In this study, a temperature-induced phase fractionation known as cloud-point extraction (CPE) with the non-ionic surfactant Triton X-114 was used to simultaneously extract, concentrate, and fractionate hydrophobic and hydrophilic proteins from mouse brain tissue. Two bottom-up proteomic techniques were used to comprehensively identify the extracted proteins. The first "shotgun"-based approach included tryptic digestion of the proteins followed by reversed-phase nanoliquid chromatography (RP-nanoLC) in combination with electrospray ionization (ESI) tandem mass spectrometry (MS/MS). In the second approach, the extracted intact proteins were first separated by one-dimensional (1D) gel electrophoresis and then in-gel digested with trypsin and analyzed with nanoLC-MS/MS. In total, 1,825 proteins were unambiguously identified and the percentage of membrane proteins was 26% which is at the reported genome expression levels of 20-30%. The protein overlap between the two approaches was high. The majority (77%) of the identifications in the first approach was also found by the second method. The protein overlap between the CPE-extracted hydrophilic and hydrophobic fractions was rather small (16-23%) for both methods, which indicates a good phase separation. A quantitative evaluation of the CPE with iTRAQ labeling and nanoLC-ESI-MS/MS analysis gave iTRAQ ratios at the expected levels and an overall variation of the entire method at 17-31%. The results indicate very reproducible sample preparation and analysis methods that readily can be applied on large-scale sample sets.

Publication types

  • Evaluation Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain Chemistry*
  • Chemical Fractionation / methods*
  • Hydrophobic and Hydrophilic Interactions
  • Membrane Proteins / isolation & purification*
  • Mice
  • Octoxynol
  • Polyethylene Glycols
  • Proteins / isolation & purification*
  • Proteomics / methods
  • Reproducibility of Results
  • Spectrometry, Mass, Electrospray Ionization
  • Tandem Mass Spectrometry
  • Temperature

Substances

  • Membrane Proteins
  • Proteins
  • Polyethylene Glycols
  • Octoxynol
  • Nonidet P-40