Interaction between sodium dodecyl sulfate and membrane reconstituted aquaporins: A comparative study of spinach SoPIP2;1 and E. coli AqpZ

Jesper Schmidt Hansen, Ardcharaporn Vararattanavech, Inés Plasencia, Per Junior Greisen, Julie Bomholt, Jaume Torres, Jenny Emnéus, Claus Helix Nielsen

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Abstract

This study describes the interaction between sodium dodecyl sulfate (SDS) and membrane proteins reconstituted into large unilamellar lipid vesicles and detergent micelles studied by circular dichroism (CD) and polarity sensitive probe labeling. Specifically, we carried out a comparative study of two aquaporins with high structural homology SoPIP2;1 and AqpZ using identical reconstitution conditions. Our CD results indicate that SDS, when added to membrane-reconstituted aquaporins in concentrations below the SDS critical micelle concentration (CMC, ~8mM), causes helical rearrangements of both aquaporins. However, we do not find compelling evidence for unfolding. In contrast when SDS is added to detergent stabilized aquaporins, SoPIP2;1 partly unfolds, while AqpZ secondary structure is unaffected. Using a fluorescent polarity sensitive probe (Badan) we show that SDS action on membrane reconstituted SoPIP2;1 as well as AqpZ is associated with initial increased hydrophobic interactions in protein transmembrane (TM) spanning regions up to a concentration of 0.1× CMC. At higher SDS concentrations TM hydrophobic interactions, as reported by Badan, decrease and reach a plateau from SDS CMC up to 12.5× CMC. Combined, our results show that SDS does not unfold neither SoPIP2;1 nor AqpZ during transition from a membrane reconstituted form to a detergent stabilized state albeit the native folds are changed.
Original languageEnglish
JournalB B A - Biomembranes
Volume1808
Issue number10
Pages (from-to)2600-2607
ISSN0005-2736
DOIs
Publication statusPublished - 2011

Keywords

  • Lipid membrane
  • Folding
  • Membrane protein
  • Aquaporin
  • Reconstitution
  • Sodium dodecyl sulfate

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