title: LC-nanospray-MS/MS analysis of hydrophobic proteins from membrane protein complexes isolated by blue-native electrophoresis.
abstract: The application of two-dimensional electrophoresis for the identification of hydrophobic membrane proteins is principally hampered by precipitation of many of these proteins during first-dimension, isoelectric focusing. Therefore new strategies towards the identification and characterization of membrane proteins are being developed. In this work we present a direct and rapid approach from blue-native gels to mass spectrometry, which allows the analyses of complete complexes and prevents protein aggregation of hydrophobic regions during electrophoresis. We combine blue-native gel electrophoresis and liquid chromatography--nanospray-iontrap tandem mass spectrometry to analyze the composition of oxidative phosphorylation complexes I, III, IV and V from bovine-heart mitochondria as a model system containing a number of highly hydrophobic proteins. Bands from blue-native gels were subjected either to in-gel or to in-solution tryptic digestion. The obtained peptide mixtures were further analyzed by liquid chromatography--tandem mass spectrometry and the corresponding proteins were identified by database search. From a total of 86 proteins, 67 protein subunits could be identified including all highly hydrophobic components, except the ND4L and ND6 subunits of complex I. We demonstrate that liquid chromatography--tandem mass spectrometry combined to blue-native electrophoresis is a straightforward tool for proteomic analysis of multiprotein complexes, and especially for the identification of very hydrophobic membrane protein constituents that are not accessible by common isoelectric focusing/sodium dodecyl sulphate gel electrophoresis.
authors.affiliation: Agilent Technologies R and D and Marketing GmbH and Co. KG, 76337 Waldbronn, Germany.
authors.forename: Anabel S
authors.initials: AS
authors.lastname: Fandiño
authors.forename: Isam
authors.initials: I
authors.lastname: Rais
authors.forename: Martin
authors.initials: M
authors.lastname: Vollmer
authors.forename: Helmuth
authors.initials: H
authors.lastname: Elgass
authors.forename: Hermann
authors.initials: H
authors.lastname: Schägger
authors.forename: Michael
authors.initials: M
authors.lastname: Karas
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D015180:Electrophoresis, Gel, Two-Dimensional / Q000379:methods*; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D008565:Membrane Proteins / Q000737:chemistry*; D008929:Mitochondria, Heart / Q000737:chemistry; D024101:Mitochondrial Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D036103:Nanotechnology; D040901:Proteomics / Q000379:methods*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D008565:Membrane Proteins; D024101:Mitochondrial Proteins