title: Efficiency of detergents at maintaining membrane protein structures in their biologically relevant forms.
abstract: High-resolution structural analysis of membrane proteins by X-ray crystallography or solution NMR spectroscopy often requires their solubilization in the membrane-mimetic environments of detergents. Yet the choice of a detergent suitable for a given study remains largely empirical. In the present work, we considered the micelle-crystallized structures of lactose permease (LacY), the sodium/galactose symporter (vSGLT), the vitamin B(12) transporter (BtuCD), and the arginine/agmatine antiporter (AdiC). Representative transmembrane (TM) segments were selected from these proteins based on their relative contact(s) with water, lipid, and/or within the protein, and were synthesized as Lys-tagged peptides. Each peptide was studied by circular dichroism and fluorescence spectroscopy in water, and in the presence of the detergents sodium dodecylsulfate (SDS, anionic); n-dodecyl phosphatidylcholine (DPC, zwitterionic); n-dodecyl-β-d-maltoside (DDM, neutral); and n-octyl-β-d-glucoside (OG, neutral, varying acyl tail length). We found that (i) the secondary structures of the TM segments were statistically indistinguishable in the four detergents studied; and (ii) a strong correlation exists between the extent of helical structure of each individual TM segment in detergents with its helicity level as it exists in the full-length protein, indicating that helix adoption is fundamentally the same in both environments. The denaturing properties of so-called 'harsh' detergents may thus largely be due to their interactions with non-membranous regions of proteins. Given the consistency of structural features observed for each TM segment in a variety of micellar media, the overall results suggest that the structure likely corresponds to its relevant biological form in the intact protein in its native lipid bilayer environment.
authors.affiliation: Division of Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.
authors.forename: David V
authors.initials: DV
authors.lastname: Tulumello
authors.forename: Charles M
authors.initials: CM
authors.lastname: Deber
mesh_terms: D018360:Crystallography, X-Ray; D003902:Detergents / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D026901:Membrane Transport Proteins / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D003902:Detergents; D008051:Lipid Bilayers; D026901:Membrane Transport Proteins; D010455:Peptides