Sequence hydropathy dominates membrane protein response to detergent solubilization.
The ability to predict from amino acid sequence how membrane protein structures will respond to detergent solubilization would significantly facilitate experimental characterization of these molecules. Here we have investigated and compared the response to solubilization by the "mild" n-dodecyl-β-D-maltoside (DDM) and "harsh" sodium dodecyl sulfate (SDS) of wild-type and point mutant "hairpin" (helix-loop-helix) membrane proteins derived from the third and fourth TM segments of the human cystic fibrosis transmembrane conductance regulator (CFTR) and the intervening extracellular loop. Circular dichroism spectroscopy, size-exclusion chromatography, and pyrene fluorescence spectroscopy were used to evaluate the secondary structures, hairpin-detergent complex excluded volumes, and hairpin compactness of the detergent-solubilized sequences. Sequence hydrophobicity is found to be the dominant factor dictating membrane protein response to detergent solubilization by DDM and SDS, with hairpin secondary structure exquisitely sensitive to mutation when DDM is used for solubilization. DDM and SDS differ principally in their ability to promote approach of TM segment ends, although hairpin compactness remains sensitive to point mutations. Our overall findings suggest that protein-protein and protein-detergent interactions are determined concomitantly, with the net hydropathy of residues exposed to detergent dominating the observed properties of the solubilized protein.
Division of Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.
Vincent G
VG
Nadeau
Arianna
A
Rath
Charles M
CM
Deber
D000595:Amino Acid Sequence; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry* / Q000235:genetics; D003902:Detergents / Q000494:pharmacology*; D005960:Glucosides / Q000494:pharmacology*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008969:Molecular Sequence Data; D017354:Point Mutation; D017433:Protein Structure, Secondary; D011721:Pyrenes / Q000737:chemistry; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology*; D012995:Solubility / Q000187:drug effects; D013050:Spectrometry, Fluorescence
D003902:Detergents; D005960:Glucosides; D011721:Pyrenes; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012967:Sodium Dodecyl Sulfate; C040358:dodecyl maltoside; C030984:pyrene