Résumé
Amphipols (APols) are amphipathic polymers with the ability to substitute detergents to keep membrane proteins (MPs) soluble and functional in aqueous solutions. APols also protect MPs against denaturation. Here, we have examined the ability of APol-trapped MPs to be analyzed by MALDI-TOF mass spectrometry (MS). For that purpose, we have used ionic and non-ionic APols and as model proteins i) the transmembrane domain of Escherichia coli outer membrane protein A, a β barrel, eubacterial MP, ii) Halobacterium salinarum bacteriorhodopsin, an α helical archaebacterial MP with a single cofactor, and iii-iv) two eukaryotic MP complexes comprising multiple subunits and many cofactors, cytochrome b6f from the chloroplast of the green alga Chlamydomonas reinhardtii and cytochrome bc1 from beef heart mitochondria. We show that these MP/APol complexes can be readily analyzed by MALDI-TOF MS; most of the subunits, some lipids and cofactors were identified. APols alone, even ionic ones, had no deleterious effects on MS signals and were not detected in mass spectra. Thus, the combination of MP stabilization by APols and MS analyses provides an interesting new approach to investigating supramolecular interactions in biological membranes.