LC-nanospray-MS/MS analysis of hydrophobic proteins from membrane protein complexes isolated by blue-native electrophoresis |
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Authors: | Fandiño Anabel S Rais Isam Vollmer Martin Elgass Helmuth Schägger Hermann Karas Michael |
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Institution: | Agilent Technologies R and D and Marketing GmbH and Co. KG, 76337 Waldbronn, Germany. |
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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. |
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Keywords: | membrane proteins hydrophobic proteins blue-native electrophoresis LC–nanospray-MS/MS tryptic digestion |
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