title: How amphipols embed membrane proteins: global solvent accessibility and interaction with a flexible protein terminus.
abstract: Amphipathic polymers called amphipols provide a valuable alternative to detergents for keeping integral membrane proteins soluble in aqueous buffers. Here, we characterize spatial contacts of amphipol A8-35 with membrane proteins from two architectural classes: The 8-stranded β-barrel outer membrane protein OmpX and the α-helical protein bacteriorhodopsin. OmpX is well structured in A8-35, with its barrel adopting a fold closely similar to that in dihexanoylphosphocholine micelles. The accessibility of A8-35-trapped OmpX by a water-soluble paramagnetic molecule is highly similar to that in detergent micelles and resembles the accessibility in the natural membrane. For the α-helical protein bacteriorhodopsin, previously shown to keep its fold and function in amphipols, NMR data show that the imidazole protons of a polyhistidine tag at the N-terminus of the protein are exchange protected in the presence of detergent and lipid bilayer nanodiscs, but not in amphipols, indicating the absence of an interaction in the latter case. Overall, A8-35 exhibits protein interaction properties somewhat different from detergents and lipid bilayer nanodiscs, while maintaining the structure of solubilized integral membrane proteins.
authors.affiliation: Institute of Physical Biology, Heinrich Heine University, Universitätsstr. 1, 40225, Düsseldorf, Germany.
authors.forename: Manuel
authors.initials: M
authors.lastname: Etzkorn
authors.forename: Manuela
authors.initials: M
authors.lastname: Zoonens
authors.forename: Laurent J
authors.initials: LJ
authors.lastname: Catoire
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Popot
authors.forename: Sebastian
authors.initials: S
authors.lastname: Hiller
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000648:ultrastructure*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D006867:Hydrolases / Q000737:chemistry* / Q000648:ultrastructure*; D057927:Hydrophobic and Hydrophilic Interactions; D011108:Polymers / Q000737:chemistry*; D011437:Propylamines / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D025941:Protein Interaction Mapping / Q000379:methods; D017434:Protein Structure, Tertiary; D012995:Solubility; D012997:Solvents / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D011108:Polymers; D011437:Propylamines; D012997:Solvents; D013501:Surface-Active Agents; C499017:amphipol A8-35; C482905:OmpX protein, E coli; D001436:Bacteriorhodopsins; D006867:Hydrolases